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Climate dynamics and extreme precipitation and flood events

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282 C.Frei et al./Climate dynamics and extremeeventsFigure1.Car buried in mud after the devastatingflashflood of the river Saltina in the town of Brig,Switzerland on24September1993.(Photo:Coffrini,Sonntags Zeitung of26September1993.)investments for the maintenance and establishment of pre-ventive measures.It is also noteworthy that few particularly severe events dominate the average costs.The two most damaging years (1987and1993)alone accounted for half of the costs from the25year period.One episode of heavy persistent pre-cipitation in July1987affected the upper Rheuss valley and damaged the trans-Alpine transport channels across the Got-thard pass–one of the main Alpine transits.In the canton of Uri,with a population of34000,the event incurred a cost estimated at340million Euro[4].These impacts have been further emphasized in series of recent episodes that include the following events:Vaison-la-Romaineflood in Septem-ber1992[5];flooding of Brig in September1993[6](see alsofigure1);Piedmontfloods in November1994[7];heavy snowfalls and avalanches in Austria and Switzerland in Feb-ruary1999;and large-scaleflooding in Switzerland in May 1999[8].The significance of extreme precipitation andflooding events for Central Europe in general and the Alps prompts consideration of changes in the frequency of their occurrence particularly in connection with anthropogenic greenhouse-gas changes to the global climate system,and the effect of changes in land-use and river hydrology.Here we as-sess past changes and possible future variations in the oc-currence of such events in Central Europe,by reviewing the relevant physical climatic processes and illustrating some of the associated inherent limitations and uncertainties.The format followed is to overview sequentially the pertinent large-scale climate dynamics(section2),the water-cycle feedbacks(section3),and the hydrological processes(sec-tion4).Thereafter the constraints upon detecting long-term trends of extremes are identified(section5),results pre-sented from a trend analyses of Alpine heavy precipitation (section6),an assessment provided of possible future fore-casting and warning methodologies(section7),andfinally a synthesis including the implications for policy analysis(sec-tion8).2.Links to the large-scale atmosphericflowExtreme weather events that occur in the vicinity of the Alps are perforce embedded within the large-scale ambient atmosphericflow.This prompts a sequence of questions: (i)Does the large-scaleflow influence the occurrence ofextreme events?(ii)What is the physical nature of the linkage(s)between the large-scaleflow and extreme events,and how is the influence manifested in terms of the climatology (frequency,intensity,spatial scale and location)of the events?(iii)Would a global climate change modify the climatology of extreme events,and could it also spawn entirely dif-ferent types of events?The focus here is on the large-scale atmosphericflow of the Atlantic-European sector and on weather events in the Alpine region.The large-scale atmosphericflow can be viewed in terms of its time-mean(monthly or seasonally averaged)and transient components.The time-meanfieldsC.Frei et al./Climate dynamics and extreme events283Figure2.Depiction of the winter season time-averaged and transient atmosphericflow features for the three decades1962–1992at500hPa:(a)the mean geopotential heightfield and the storm track pattern;(b)an NAO-like co-variation of the height and storm track departures from the mean.In these panels the heightfield is portrayed with isolines and the storm track signals are shaded.(c)Trend(shaded)and time-mean(isolines)of the storm trackfield over the specified time-period.Storm track patterns are calculated using band-pass(2.5–8days)filtered500hPa geopotentialfields(see[18]).(Units:geopotential meters.)form circumpolar patterns with superimposed wave-like variations(figure2(a)),and the Alps are located downstream of a major trough over the Western Atlantic.The transient fields are dominated by low(cyclonic)pressure systems that develop off the eastern seaboard of North America and on the south side of the Alps–regions coincident with the troughs in the time-meanfield.The Atlantic systems traverse eastward to form the so-called storm-track(figure2(a)),and the Alps are located downstream and equatorward of this track.284 C.Frei et al./Climate dynamics and extremeeventsFigure 3.Illustrations of the upper-tropospheric flow structure that preceded four events of heavy precipitation on the Alpine southside.Each pane l shows the wind vectors of the flow field and the presence of a streamer (shaded,potential vorticity)on a tropopause-level surface (200hPa,about 11.5km).(From [12].)Both the time-mean and transient components undergoa strong seasonal cycle,e.g.,the Atlantic storm track isstronger and located more poleward during winter.Thereare also distinctive interannual and decadal variations of thetime-mean fields in the form of distinct teleconnection pat-terns,i.e.,spatially coherent anomalies that undergo syn-chronous but irregular reversal in sign [9].In the Atlantic-European sector the most prominent teleconnection is theNorth Atlantic Oscillation (NAO)(see,e.g.[10]).It is char-acterized by departures away from the time-mean that are ofopposing sign and located over the Icelandic and the Azoresregions (figure 2(b)).Its positive (negative)phase corre-sponds to reduced (increased)pressure over Iceland and acorresponding enhancement (reduction)in the strength ofthe westerly flow in mid-Atlantic,and a realignment and ex-tension (reduction)of the storm track toward (away from)Scandinavia (figure 2(b)).The NAO phases correlate with the temperature (but not the precipitation)of the Alpine re-gion.Now we turn to consider question (i).There is abundant circumstantial evidence linking extreme European weather events with the large-scale flow.Rapid heavy rain and wind storms on the Alpine northside [11]and prolonged heavy rain events on the southside [12]are usually accompanied by strong transient flow features in the upper troposphere re-ferred to as streamers (see figure 3).Again prolonged dry spells over the Iberian peninsula and Morocco correlate no-tably with sustained positive phases of the NAO with its high (anticyclonic)pressure pattern over the Azores [13,14].In-deed the end of an extended drought over the Iberian penin-C.Frei et al./Climate dynamics and extreme events285sula in1995coincided with a notable reversal in phase of the NAO(see,e.g.[15]).For consideration of question(ii)the foregoing examples serve to illustrate two types of physical linkages between the large-scaleflow and extreme events.First localized short-time scale storms are linked to individual transient features in the upper-levelflow.In particular a storm’s intensity is linked to the amplitude of the feature,its duration is es-tablished essentially by the feature’s movement across the Alpine region,and its location influenced by both the lo-cation of the feature aloft and the Alpine terrain.Second regional and sub-continental spells are linked to sustained anticyclonicflow features with their intensity,duration and location determined principally by the large-scaleflow.Thus this simple categorization couples storms with transient fea-tures of the large-scaleflow and spells to sustained features.There are however more subtle linkages.For example the sequence of heavy Alpine snow“storms”of the1998–1999winter was associated with an anomalous strong and persistent north-westerlyflow.Also the transient and sus-tained features of the large-scaleflow are themselves inter-linked,and there are indications that the time-meanfields in the region of cyclogenesis influence the structure of the maturing and matured cyclones downstream.In particular the appearance of a streamer over the Eastern Atlantic is as-sociated with more anticyclonic time-mean environment in mid-Atlantic,and the streamer itself accounts for events of heavy rainstorms on the Alpine southside.In effect there is a“phenomena-chain”linking the far-field time-mean pattern to the occurrence of local extreme events.Question(iii)relates to the impact of a global climate change upon Alpine extreme events.Here we discuss sep-arately the in situ and far-field effects.In situ effects will result from a mere change in the temperature and humid-ity of the airflow and weather systems incident upon the Alps.A temperature change would yield a change in the fre-quency distribution of warm and cold spells,and additional moistureflux into the region coupled with orographically-induced precipitation would favor increased severity of rain-storms.Such an effect has been calibrated in model sim-ulations of the regional climate[16].Note however that a warmer incident atmosphere and increased moistureflux would have a contrasting effect upon snowstorms,and the net impact upon the snowfall(and its subsequent melt)is more difficult to assess.For the far-field effects the impact will hinge critically upon whether climate change will manifest itself via a change in the frequency of the atmosphere’s natural in-terannual teleconnection patterns.The increase in global mean temperatures over the last few decades can be ac-counted for by the observed decadal-scale strengthening of the NAO[10,17].There has also been an accompanying change(seefigure2(c))in the eastward extent of the Atlantic storm track towards Europe[18].These effects are consis-tent with a change in the relative frequency of the phases of the NAO,rather than in a change to a different or new type of teleconnection pattern,but clearly there are implications for the occurrence and frequency of extreme events downstream over Europe.The paradigm that climate change will manifest itself via changes in the frequency and amplitude of existing telecon-nection patterns carries important ramifications.It serves to underline the desirability of enhancing our understanding of and ability to predict these patterns and the associated“phe-nomena chain”.It also suggests that there could be a change in the frequency and intensity(but not necessarily the type) of extreme events.The issue of predicting these features of extreme events is taken up again in section7.3.Climate change and the intensification of the watercycleThe total vertically integrated water content of the at-mosphere amounts to as little as∼25mm,and this repre-sents∼0.001%of the overall global(fresh and sea)water resources.Despite its small amount,atmospheric water(in the form of water vapor,water droplets,and ice crystals) is one of the most important factors in our climate system and participates in several key feedback processes:Water vapor is the most important greenhouse gas and thereby af-fects the infrared radiation budget;clouds as well as surface snow cover reflect incident sunlight and thereby affect the visible radiation budget;andfinally phase transitions of wa-ter in the atmosphere closely couple the atmospheric water and energy cycles.This latter coupling is so highly efficient due to the extremely large value of the latent heat of vapor-ization/condensation.The coupling of the water cycle with the atmospheric cir-culation takes place on many levels.Associated radiative forcing and latent heating may drive,amplify or weaken at-mospheric circulations such as planetary-scale circulations, low-pressure systems in the mid-latitudes;meridional and monsoonal circulations in the tropics;as well as embedded circulations on the mesoscale.The redistribution of water substance by precipitation may feed back to the ocean since precipitation and freshwater runoff from the continents pro-vides a driving agent for oceanic circulations.In turn,such changes may also feed back to the local precipitation cli-mate.Overall,an assessment of climate change and its water cycle thus requires a fully integrated assessment,interac-tively accounting for all the relevant key feedbacks.Nev-ertheless–it is justified to specifically review in this section aspects of the temperature–moisture feedback,for its major potential importance in climate change.This feedback links climate change with a moistening of the atmosphere and an intensification of the hydrological cycle.Such a moisten-ing could have major repercussion upon a wide range of cloud and precipitation processes,and contribute directly to changes in the regional hydrological response.The basic premise of the temperature–moisture feedback is based on the observation that the atmospheric water va-por content is primarily controlled by the temperature depen-dence of the saturation mixing ratio,rather than by changes286 C.Frei et al./Climate dynamics and extreme eventsin relative humidity.Observed interannual and intraseasonal variations of the atmospheric moisture content lend support to this general behavior in the middle and high latitudes (e.g.[19,20])but not in the tropics[21].Similarly,observa-tions show that the atmosphere has not only become warmer during this century,but also moister–at a rate which is ap-proximately consistent with the temperature dependency of the saturation mixing ratio(e.g.[20,22]).In agreement with the above premise,simulations un-dertaken with global climate models(GCMs)suggest that a global-scale climate warming could be associated with a substantial increase in the column-integrated atmospheric moisture content(e.g.[23]).The results suggest an increase of the atmospheric moisture content by about7%per degree of warming.The moistening of the atmosphere as a result of green-house gas forcing is due to several factors.First,greenhouse gas forcing implies an increase of the incoming infrared ra-diation at the surface,and this not only warms the bound-ary layer but also enhances the hydrological cycle,as much of the heating at the surface goes into evaporating surface moisture[24–26].Second,evaporation over sea and evap-otranspiration over moist land surfaces are approximately proportional to the saturation humidity deficit.Thus,even when assuming constant relative humidity in the planetary boundary layer,changes in evapotranspiration have a sim-ilar temperature dependency as the saturation mixing ratio itself.Together these two factors imply an intensification of evaporation and ultimately of the whole hydrological cycle with increasing surface energy balance and temperature.In-deed,under current climatic conditions,around80%of the net surface energy balance are converted into evapotranspi-ration,and only20%are converted into surface sensible heat fluxes[24,27].Thus,the energetic effects of climate change associated with changes in the hydrological cycle may be more substantial than those resulting from direct thermal ef-fects.While the observed and simulated atmospheric moisten-ing establishes a fairly close relationship between the at-mospheric moisture content and the saturation mixing ra-tio except for the tropics,globally averaged evapotranspi-ration and precipitation rates in GCM simulations appear to increase at a substantially slower rate(see,e.g.[24,28–30]). The prime reason for this behavior is probably the domi-nance of oceanic evaporation,and the fact that the sea sur-face temperature warms at a slower rate than global surface temperature.Considerations of the atmospheric water bal-ance then imply that the averaged residence time of the wa-ter molecules in the atmosphere is increased in current GCM experiments of climate change[26].Such an increase in residence time might be associated with a reduction of the space/time fraction within which precipitation falls.Yet,at the same time,there is a net increase in globally averaged precipitation.A critical question regarding the intensification of the hy-drological cycle is thus its impact on the frequency-intensity distribution of precipitation events.All GCMsimulations Figure4.Change in daily precipitation statistics(frequency change as afunction of threshold)simulated with a regional climate model for a surro-gate climate change scenario(—)and derived from a scaling of the empiri-cal probability density function(---).Results are valid for the autumn sea-son and for three subregions in Central Southern Europe.The large-scalescenario is characterized by a uniform temperature increase by2degreesand a15%increase of the atmospheric moisture(unchanged relative hu-midity).The climate model mimics the regional effects of“climate moist-ening”.(From16.)with increased greenhouse gas concentrations suggest someenhancement of the hydrological cycle and most provide also some indication of an attendant shift towards more nu-merous events of heavy precipitation[31,32].The latter effect has been interpreted in terms of a simple moisture-precipitation feedback.Since only about20%of the precip-itation comes from evaporation within a distance of about 1000km[26],precipitation is usually more directly linked tothe atmospheric moisture content than to nearby evapotran-spiration.Fowler and Hennessy[33]pointed out that an as-sociatedflat percentage increase of each precipitation event(scaling of the precipitation probability density function)by ∼20%,which corresponds to a temperature–moisture feed-back of∼3K,might ultimately lead to a strong increase in the frequency of heavy precipitation events.For midlat-itude conditions and stratiform precipitation processes,thishypothesis has been confirmed by a regional climate model-ing study(figure4,[16]):The simulated changes in precip-itation frequency resulting from a warming and moistening are found to be comparatively minor for weak events but ex-hibit a strongly progressive increase with the event size.As shown infigure4,the simulated changes in the precipitation statistics are found to be in good agreement with the scaling hypothesis.In addition to the moisture content,the nature of theresponse will depend on many additional factors such aschanges in storm track dynamics,soil moisture conditions, cloud formation processes,atmospheric stratification,and the relative importance of stratiform versus convective pre-cipitation.Since the last IPCC report[34]additional sce-narios using global and regional models have become avail-able.For equilibrium doubling of carbon dioxide,Hennessy et al.[35]find that for a given return period of1year thereC.Frei et al./Climate dynamics and extreme events287is an increase of the precipitation intensity by10–25%in Europe,USA,Australia,and India.For a given precipita-tion intensity,the return periods becomes shorter by a fac-tor2–5.McGuffie et al.[36]confirm this conclusion when comparing the behavior offive different GCMs.Zwiers and Kharin[37]compute the changes of event size with a return period of20years in equilibrium integrations.In the CO2 doubling experiment theyfind an increase of the likelihood for heavy precipitation almost worldwide with maximum ab-solute changes in event size in the tropics and over India. Jones et al.[38]use a regional model with about∼50km resolution driven by a global model.Over Europe,both the driving GCM and the regional modelfind frequency in-creases for events exceeding10mm/day by between12and 50%throughout the year.In relation to precipitation in the Alpine and pre-Alpine region,the temperature–moisture feedback is likely to play an important role during the colder seasons,when the water cycle is primarily determined by sea-to-land transport,and when convective precipitation is not overly important.The associated changes in the frequency of extreme events will be modulated by changes in the synoptic scale circulation (cf.section2)and will be particularly sensitive to weather patterns with strong warm and moistflow towards the Alps.During the summer season,however,changes in heavy precipitation events are more difficult to assess,as these are affected by additional factors.The uncertainty comes from the fact that summer precipitation over the European con-tinent is affected by the underlying land surface.During episodes of active convection,evapotranspiration and thus soil moisture dynamics as well as cloud-radiative feedbacks become highly relevant,thus questioning the direct applica-bility of the temperature–precipitation feedback.Climate change scenarios derived from GCM experi-ments have indeed detected–despite the global intensifi-cation of the hydrological cycle and the associated increase of mean precipitation–an increased likelihood for the oc-currence of drought conditions in semi-arid regions[39,40]. The prime reason are increases in evapotranspiration,which are efficiently reducing the summer-time soil moisture con-tent.Surface conditions(albedo,soil moisture content,veg-etation,and snow cover)determine the evolution of sur-face variables in response to the larger-scale synoptic forc-ing,and related changes may feed back to the near surface climate[41,42]and ultimately also to the precipitation re-sponse[43].Beside numerical simulations,there is also observational evidence from lagged correlation analysis be-tween soil-moisture conditions and subsequent precipitation for such effects to be active in the middle latitudes[44].In relation to the European and Alpine climate,analysis of the literature suggests that with climate change the semi-arid regions of southern Europe may experience drier condi-tions during summer and autumn.To the extent that much of the Alpine summertime convection occurs with slightly south-easterlyflow,this might yield a concomitant reduction of Alpine precipitation.However,this hypothesis is specu-lative at present,as it does not properly integrate changes in ambient atmospheric circulation.Additional numerical ex-periments of the aforementioned feedbacks are thus needed, along with model improvements of the relevant processes to assess the fate of summer precipitation over Europe.4.Climate change,hydrological processes,andlarge-scalefloodingAtmospheric processes can spawn heavy/extended pre-cipitation with the potential forflooding,but much of the resulting impact is ultimately controlled by hydrological processes at the surface and in the soils,determining the evo-lution and peek level of river runoff.These processes are particularly relevant forflooding events along rivers drain-ing large-scale basins of several thousand square kilometers. Several of the major European river systems originate in the Alpine ridge(Po,Rhone,Danube,Rhine).This section ex-plains the conditions forflood initiation and runoff processes controlling large-scale riverfloods and it discusses,at the ex-ample of the river Rhine,the potential role of anthropogenic influences and future prospects of large-scalefloods.4.1.Flood initiation andflood-generating hydrologicalprocessesPrecipitation and temperature are decisive meteorologi-cal variables for the release of aflood.Besides the basin-and time-integrated precipitation amounts,the temporal evo-lution and spatial distribution within the catchment play an essential role for the development of and the partition into the various runoff components(see below),and for the rel-ative timing of the peek runoff between the tributaries.Sur-face air temperature determines the partitioning into snow and rain during the precipitation event and–in combina-tion with radiation and surface winds–controls the runoff from snow and glacier melt and determines the amount of re-evaporation from soils and vegetation.Temperature and humidity conditions of the soils at the instant of the precipitation event are important initial fac-tors to the evolution of aflood.Frozen or moisture-saturated soils have a limited infiltration and moisture-storage capac-ity,which tends to accelerate the runoff process.Hence the generation of aflood also critically depends on the meteoro-logical history prior to the heavy precipitation episode.Theflood hydrograph consists of several main runoff components characterized by different runoff velocities. Surface runoff refers to waters routed at the surface or within the top soil layers and the river beds.Surface runoff re-acts quickly to excessive water,and the response-time of a river system to precipitation is largely depending on the fraction of surface runoff.Interflow refers to the delayed runoff through layered soils.This component also reaches the catchment river network and contributes to the total out-flow at the watershed outlet.Response times of the interflow component depend on the permeability of the soils,with less permeable soils being generally characterized by a higher288 C.Frei et al./Climate dynamics and extreme eventsflow channel density and hence faster response times and higherflood potential.Baseflow or ground-waterflow refers to the water runoff into the deep soils.It is the predomi-nant runoff component during dry weather conditions,but it has,in general,only a small portion to the hydrograph of a flooding event.Three hydrological stages of aflood evolution can be distinguished:(1)The generation and partition of the var-ious run-off components.Apart from the meteorological conditions,this process is controlled by a range of physio-graphic catchment characteristics,such as the topography, slope,landcover,landuse,vegetation,water storage capaci-ties as well as soil conductivity and stratification.Theflood potential is enhanced in situations that allow a high fraction of surface runoff.(2)The runoff concentration determines the pathways of the various runoff components through the catchment river network and subsurfaceflow channels to the watershed outlet.A highflood potential is achieved when surface runoff from various parts of the catchment and sub-surfaceflows are in phase.(3)Theflood routingfinally de-termines theflow of water masses through the tributary net-work to the main river.Riverbed geometry,slope and rough-ness determine the speed of this runoff.The peek water level and the duration offloods along the main river will critically depend on the runoff timing between tributaries.The ex-istence of natural retention areas,lakes,manmade storage reservoirs,and dams can moderate the peek level andflood-ing impacts.rge-scaleflooding in the Rhine river basinThe Rhine river basin(see the geographical map infig-ure5)covers an area of185300km2.The main river length is about1300km.The basin represents landscapes from the mountainous parts of the Alps and numerous hilly catch-ments(i.e.,V osgues,Black Forest)down to the lowlands of Western Germany and the Netherlands.The Rhine basin touches nine countries and belongs to the large rivers in Eu-rope with a relatively high discharge per unit area(mean in Cologne14.3l s−1km−2for the period1891–1998).In contrast to other rivers,the seasonal variations of runoff are relatively small.This is due to the various runoff regimes within the different subcatchments and regions[45].The Rhine river can be divided into six main parts(figure5): The Alpine Rhine(from its source to the Lake of Constance) and the High Rhine(from the Lake of Constance to Basel)–both with alpine catchment character;the Upper Rhine (between Basel and Bingen,including the tributaries Neckar and Main)and the Middle Rhine(between Bingen and Bonn, including the tributary Mosel)–both characterized by hilly catchments;the Lower Rhine(from Bonn to the German-Dutch border)and the Rhine-Delta–both located within lowland.Figure6shows the mean runoff regimes(mean monthly discharges)at different gauging stations,which represent the various regions of the Rhine river.The average runoff regime of the Alpine rivers is dominated by snowmelt,and Figure5.Map of the Rhine river basin in Central Europe,including geo-graphical names,tributaries,and major river gauges mentioned in thetext. Figure6.Annual cycle of long-term mean runoff observed atfive river-gauges along the Rhine river,demonstrating the downstream variation of runoff regimes.Portions of areas for the subcatchments intermediate to the respective river gauges are:Alpine Rhine3.3%(1.4%glacier covered), Alpine and High Rhine18.6%(1.3%glacier covered),Upper Rhine18.6%,Middle Rhine18.8%,and Lower Rhine19.5%.from the high-altitude parts of the basin also glacier melt contributes.The discharge is governed by glacial and ni-val regimes with a pronounced maximum in summer and a minimum in winter.In the lower catchment parts,the maxi-。

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tpo32三篇托福阅读TOEFL原文译文题目答案译文背景知识

tpo32三篇托福阅读TOEFL原文译文题目答案译文背景知识

tpo32三篇托福阅读TOEFL原文译文题目答案译文背景知识阅读-1 (2)原文 (2)译文 (5)题目 (7)答案 (16)背景知识 (16)阅读-2 (25)原文 (25)译文 (28)题目 (31)答案 (40)背景知识 (41)阅读-3 (49)原文 (49)译文 (53)题目 (55)答案 (63)背景知识 (64)阅读-1原文Plant Colonization①Colonization is one way in which plants can change the ecology of a site. Colonization is a process with two components: invasion and survival. The rate at which a site is colonized by plants depends on both the rate at which individual organisms (seeds, spores, immature or mature individuals) arrive at the site and their success at becoming established and surviving. Success in colonization depends to a great extent on there being a site available for colonization – a safe site where disturbance by fire or by cutting down of trees has either removed competing species or reduced levels of competition and other negative interactions to a level at which the invading species can become established. For a given rate of invasion, colonization of a moist, fertile site is likely to be much more rapid than that of a dry, infertile site because of poor survival on the latter. A fertile, plowed field is rapidly invaded by a large variety of weeds, whereas a neighboring construction site from which the soil has been compacted or removed to expose a coarse, infertile parent material may remain virtually free of vegetation for many months or even years despite receiving the same input of seeds as the plowed field.②Both the rate of invasion and the rate of extinction vary greatly among different plant species. Pioneer species - those that occur only in the earliest stages of colonization -tend to have high rates of invasion because they produce very large numbers of reproductive propagules (seeds, spores, and so on) and because they have an efficient means of dispersal (normally, wind).③If colonizers produce short-lived reproductive propagules, they must produce very large numbers unless they have an efficient means of dispersal to suitable new habitats. Many plants depend on wind for dispersal and produce abundant quantities of small, relatively short-lived seeds to compensate for the fact that wind is not always a reliable means If reaching the appropriate type of habitat. Alternative strategies have evolved in some plants, such as those that produce fewer but larger seeds that are dispersed to suitable sites by birds or small mammals or those that produce long-lived seeds. Many forest plants seem to exhibit the latter adaptation, and viable seeds of pioneer species can be found in large numbers on some forest floors. For example, as many as 1,125 viable seeds per square meter were found in a 100-year-old Douglas fir/western hemlock forest in coastal British Columbia. Nearly all the seeds that had germinated from this seed bank were from pioneer species. The rapid colonization of such sites after disturbance is undoubtedly in part a reflection of the largeseed band on the forest floor.④An adaptation that is well developed in colonizing species is a high degree of variation in germination (the beginning of a seed’s growth). Seeds of a given species exhibit a wide range of germination dates, increasing the probability that at least some of the seeds will germinate during a period of favorable environmental conditions. This is particularly important for species that colonize an environment where there is no existing vegetation to ameliorate climatic extremes and in which there may be great climatic diversity.⑤Species succession in plant communities, i.e., the temporal sequence of appearance and disappearance of species is dependent on events occurring at different stages in the life history of a species. Variation in rates of invasion and growth plays an important role in determining patterns of succession, especially secondary succession. The species that are first to colonize a site are those that produce abundant seed that is distributed successfully to new sites. Such species generally grow rapidly and quickly dominate new sites, excluding other species with lower invasion and growth rates. The first community that occupies a disturbed area therefore may be composed of specie with the highest rate of invasion, whereas the community of the subsequent stage may consist of plants with similar survival ratesbut lower invasion rates.译文植物定居①定居是植物改变一个地点生态环境的一种方式。

气候的影响英语作文

气候的影响英语作文

Climate change is one of the most pressing global issues of our time,with farreaching implications for the environment,economy,and society.The effects of climate change are multifaceted and can be observed in various aspects of life on Earth.1.Environmental Impact:The most evident impact of climate change is on the environment.Rising temperatures have led to the melting of polar ice caps and glaciers, causing sea levels to rise.This not only threatens coastal cities and lowlying islands but also disrupts the habitats of many species,leading to a loss of biodiversity.Additionally, climate change has been linked to more frequent and severe weather events,such as hurricanes,floods,and droughts,which can devastate ecosystems and human settlements.2.Agricultural Effects:Agriculture is heavily dependent on stable climate conditions. Changes in temperature and precipitation patterns can lead to reduced crop yields, affecting food security globally.Droughts can decimate harvests,while floods can destroy crops and soil fertility.Moreover,warmer temperatures can shift the ranges of pests and diseases,complicating agricultural practices.3.Health Implications:Climate change can have direct and indirect effects on human health.Direct effects include heatrelated illnesses and deaths during heatwaves.Indirect effects are more complex and can include the spread of vectorborne diseases as warmer climates expand the habitats of diseasecarrying insects.Additionally,air quality can be affected by higher temperatures,exacerbating respiratory issues.4.Economic Consequences:The economic impacts of climate change are significant and varied.Industries such as agriculture,fisheries,and tourism are particularly vulnerable to the effects of climate change.Insurance costs may rise due to an increase in natural disasters,and infrastructure may require costly adaptations to withstand extreme weather events.On the other hand,some regions may experience economic benefits from a longer growing season or access to new shipping routes.5.Social and Political Ramifications:Climate change can exacerbate social inequalities and lead to political instability.Displacement of populations due to environmental disasters can create refugee crises,straining international relations and local resources. Additionally,competition for dwindling resources like water and arable land can lead to conflicts.6.Mitigation and Adaptation Efforts:In response to the impacts of climate change,there is a growing emphasis on mitigation and adaptation strategies.Mitigation involves reducing greenhouse gas emissions to slow the rate of climate change,while adaptation involves adjusting to the effects that are already occurring.This can include developingmore resilient infrastructure,investing in renewable energy,and implementing policies that promote sustainable development.cation and Awareness:Raising awareness about the impacts of climate change is crucial for driving societal and political cation plays a key role in informing the public about the science behind climate change,its consequences,and the steps that can be taken to mitigate its effects.8.International Cooperation:Addressing climate change requires a coordinated global response.International agreements,such as the Paris Agreement,aim to unite countries in efforts to reduce emissions and support those most vulnerable to climate change impacts.In conclusion,the impacts of climate change are widespread and interconnected, affecting every aspect of life on Earth.It is essential that individuals,communities,and nations work together to mitigate these effects and adapt to the changes that are already underway.。

2024年统招专升本英语考试真题及答案

2024年统招专升本英语考试真题及答案

2024年统招专升本英语考试真题及答案全文共3篇示例，供读者参考篇1Title: 2024 National Unified Entrance Examination English Exam Questions and Answers for Part-time UndergraduatesIntroduction:The National Unified Entrance Examination for part-time undergraduates is a key milestone for individuals looking to further their education through specialized programs. In 2024, the English exam questions have been carefully crafted to assess candidates' language proficiency and comprehension skills. In this document, we will provide a comprehensive overview of the exam questions and answers for aspiring part-time undergraduates.Section 1: Reading Comprehension (45 points)Question 1:Read the following passage and answer the questions below:"Climate change is one of the most pressing issues facing our planet. Rising temperatures, extreme weather events, andmelting ice caps are all signs of the impact of human activities on the environment. To combat climate change, we must take action now by reducing our carbon footprint, investing in renewable energy sources, and promoting sustainable practices."Question 1.1: What are some of the signs of climate change mentioned in the passage?Question 1.2: What are three ways mentioned in the passage to combat climate change?Answers:1.1: Rising temperatures, extreme weather events, and melting ice caps are signs of climate change.1.2: Reducing our carbon footprint, investing in renewable energy sources, and promoting sustainable practices are ways to combat climate change.Question 2:Read the following passage and answer the questions below:"Artificial intelligence (AI) is revolutionizing various industries by improving efficiency, accuracy, and innovation. From autonomous vehicles to medical diagnostics, AI has the potential to transform how we live and work. However, concernsabout AI ethics, privacy, and job displacement have also emerged."Question 2.1: What are some benefits of artificial intelligence mentioned in the passage?Question 2.2: What are some concerns related to artificial intelligence mentioned in the passage?Answers:2.1: Improving efficiency, accuracy, and innovation are benefits of artificial intelligence.2.2: Concerns about AI ethics, privacy, and job displacement are mentioned in the passage.Section 2: Writing (30 points)Question 1:Write an essay of at least 300 words on the following topic: "The Importance of Lifelong Learning in a Globalized World."Answer: (Sample essay)In today's globalized world, the pace of change and innovation is ever-accelerating, making lifelong learning more crucial than ever before. Lifelong learning is the process ofacquiring new knowledge and skills throughout one's life, enabling individuals to adapt to new challenges and opportunities. This continuous pursuit of learning not only enhances personal growth but also contributes to individual and societal success.One of the key benefits of lifelong learning is its ability to enhance personal development and career advancement. In a rapidly changing job market, individuals who prioritize lifelong learning are better equipped to acquire new skills, stay relevant in their fields, and seize opportunities for growth. Lifelong learners are also more adaptable and resilient in the face of technological advancements and economic shifts, making them valuable assets in the workforce.Moreover, lifelong learning promotes intellectual curiosity, creativity, and critical thinking skills. By engaging in lifelong learning activities such as reading, attending workshops, or pursuing further education, individuals can expand their knowledge base, stimulate their minds, and foster a culture of innovation. In a globalized world where creativity and problem-solving are highly valued, lifelong learners are more likely to contribute to the advancement of society and address complex challenges.In conclusion, lifelong learning plays a vital role in empowering individuals to thrive in a globalized world. By embracing a mindset of continuous growth and development, individuals can adapt to change, expand their horizons, and contribute to a more prosperous and sustainable future for all. Embracing lifelong learning is not only a personal choice but a societal imperative in today's dynamic and interconnected world.Section 3: Listening Comprehension (25 points)Instructions: Listen to the audio clips and answer the questions below.Question 1: (Audio clip)What is the speaker talking about?Answers: (based on audio content)The speaker is discussing the benefits of volunteering and its impact on communities.Question 2: (Audio clip)What are the speaker's recommendations for effective time management?Answers: (based on audio content)The speaker recommends setting priorities, delegating tasks, and using technology to manage time effectively.Conclusion:The 2024 National Unified Entrance Examination forpart-time undergraduates includes a comprehensive assessment of candidates' English language skills through reading comprehension, writing, and listening exercises. By familiarizing themselves with the exam questions and answers provided in this document, aspiring part-time undergraduates can prepare effectively for the exam and enhance their chances of success. Good luck to all candidates!篇22024年统招专升本英语考试真题及答案Section I Listening Comprehension (30 points)Part A (10 points)Directions: In this part, you will hear ten short dialogues. At the end of each dialogue, a question will be asked about what was said. Both the dialogue and the question will be spoken only once. After you hear a dialogue and the question about it, readthe four possible answers on your paper, and decide which one is the best answer to the question you have heard.1. What does the woman want?A. A glass of water.B. A cup of tea.C. Some coffee.D. A bottle of soda.2. How is the man feeling now?A. Nervous.B. Excited.C. Upset.D. Satisfied.3. What is the woman looking for?A. Her keys.B. Her phone.C. Her wallet.D. Her glasses.4. What did the woman forget to bring?A. Her umbrella.B. Her ID card.C. Her lunch.D. Her purse.5. What time will the meeting start?A. At 8:30.B. At 9:00.C. At 9:30.D. At 10:00.6. How will the man get to the airport?A. By taxi.B. By bus.C. By car.D. By subway.7. What is the woman’s job?A. A teacher.B. A doctor.C. A lawyer.D. An accountant.8. When is the woman’s birthday?A. In January.B. In February.C. In March.D. In April.9. What is the man’s favorite food?A. Pizza.B. Sushi.C. Pasta.D. Hamburger.10. Why is the man calling the woman?A. To make an appointment.B. To cancel a meeting.C. To ask for directions.D. To say thank you.Part B (10 points)Directions: In this part, you will hear two passages. At the end of each passage, you will hear five or six questions. Both the passage and the questions will be spoken only once. After you hear a question, read the four possible answers on your paper, and decide which one would be the best answer to the question you have heard.Passage OneQuestions 11-1511. What is the speaker’s favorite hobby?A. Reading books.B. Watching movies.C. Playing sports.D. Traveling.12. How does the speaker feel about music?A. She enjoys it.B. She dislikes it.C. She is indifferent.D. She hates it.13. What does the speaker say about her job?A. It is boring.B. It is stressful.C. It is rewarding.D. It is flexible.14. What does the speaker do in her free time?A. Hang out with friends.B. Volunteer at a charity.C. Go to the gym.D. Paint pictures.15. What book does the speaker recommend?A. The Great Gatsby.B. Pride and Prejudice.C. To Kill a Mockingbird.D. Harry Potter.Passage TwoQuestions 16-2016. What is the passage mainly about?A. The benefits of exercise.B. The importance of healthy eating.C. The dangers of smoking.D. The effects of stress.17. How many hours of sleep is recommended for adults?A. 5-6 hours.B. 7-8 hours.C. 9-10 hours.D. 11-12 hours.18. What is the speaker’s advice on diet?A. Skip breakfast.B. Eat fast food.C. Avoid sugar.D. Drink soda.19. What does the speaker suggest for reducing stress?A. Taking a vacation.B. Watching TV.C. Working longer hours.D. Sleeping less.20. What is the speaker’s final advice?A. Exercise regularly.B. Eat more vegetables.C. Quit smoking.D. Meditate daily.Section II Use of English (20 points)Directions: Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C, or D on your answer sheet.Since the invention of the smartphone, many people have become 21 on social media. It is not uncommon to see individuals completely immersed in their phones, 22 to the world around them. This behavior can have negative consequences for one’s social life. Instead of having face-to-face interactions,people are opting for virtual 23, which can lead to feelings of loneliness and isolation.Moreover, the excessive use of social media can impact one’s mental health. The constant need for validation 24 likes and comments can make individuals anxious and even depressed. Studies have shown that heavy social media users are more likely to experience 25 levels of anxiety and stress compared to those who use social media sparingly.It is important to remember that social media is a tool, not a substitute for real-life connections. While it can be a useful platform for staying in touch with friends and family, it should not be the sole means of communication. 26, it is essential to set boundaries and prioritize face-to-face interactions to maintain healthy relationships and mental well-being.21. A. addicted B. dependent C. fascinated D. obsessed22. A. oblivious B. unaware C. indifferent D. clueless23. A. discussions B. conversations C. exchanges D. dialogues24. A. on B. by C. for D. with25. A. high B. elevated C. increased D. heightened26. A. In addition B. On the contrary C. Therefore D. FurthermoreSection III Reading Comprehension (40 points)Part A (10 points)Directions: Read the following passage and answer the questions that follow.The Benefits of Outdoor ExerciseSpending time outdoors has numerous benefits for both physical and mental health. One of the main advantages of outdoor exercise is the exposure to natural sunlight, which allows the body to absorb vitamin D. This essential nutrient plays a key role in bone health and immune function.Additionally, outdoor activities such as hiking, biking, and jogging provide an opportunity to connect with nature and reduce stress levels. Research has shown that spending time in green spaces can improve mood and cognitive function.Furthermore, outdoor exercise can increase motivation and engagement compared to indoor workouts. The variety of terrains and the changing scenery can make workouts more enjoyable and challenging.27. What is one of the benefits of outdoor exercise mentioned in the passage?A. Improved heart healthB. Enhanced creativityC. Increased vitamin C absorptionD. Better immune function28. According to the passage, how can spending time outdoors reduce stress levels?A. By increasing exposure to natural sunlightB. By engaging in physical activitiesC. By consuming vitamin D supplementsD. By avoiding indoor environments29. Which of the following activities is NOT mentioned as an outdoor exercise in the passage?A. SwimmingB. HikingC. BikingD. Jogging30. How does outdoor exercise differ from indoor workouts, according to the passage?A. It requires less motivationB. It offers less varietyC. It is more engagingD. It is less challengingPart B (30 points)Directions: Read the following passages. Answer the questions according to the information given in the passages.Passage OneThe Impact of Climate ChangeClimate change is a global issue that poses significant threats to the planet. The rise in average global temperatures has led to extreme weather events such as hurricanes, droughts, and wildfires. These environmental disasters have devastating consequences for ecosystems, wildlife, and human populations.In addition to the immediate impacts of climate change, there are long-term effects that will have lasting repercussions. Rising sea levels, melting ice caps, and ocean acidification are allcontributing to the decline of biodiversity and the destruction of natural habitats.It is essential for governments, industries, and individuals to take action to combat climate change and reduce carbon emissions. Sustainable practices, renewable energy sources, and conservation efforts are crucial in mitigating the effects of global warming.31. What are some of the extreme weather events caused by climate change mentioned in the passage?A. Floods and blizzardsB. Earthquakes and tsunamisC. Hurricanes and droughtsD. Tornadoes and heatwaves32. What are some of the long-term effects of climate change discussed in the passage?A. Volcanic eruptions and landslidesB. Biodiversity decline and habitat destructionC. Disease outbreaks and water contaminationD. Deforestation and soil erosion33. According to the passage, what is needed to combat climate change?A. Increased carbon emissionsB. More natural disastersC. Sustainable practices and conservation effortsD. Deforestation and pollutionPassage TwoThe Benefits of BilingualismResearch has shown that being bilingual has numerous cognitive benefits. Bilingual individuals have been found to have improved problem-solving skills, better multitasking abilities, and enhanced creativity compared to monolingual speakers.Furthermore, being bilingual can delay the onset ofage-related cognitive decline and reduce the risk of neurodegenerative diseases such as Alzheimer's. The constant need to switch between languages and juggle linguistic rules can keep the brain active and agile.In addition to cognitive advantages, bilingualism can also provide social and cultural benefits. Bilingual individuals have theopportunity to communicate with a wider range of people and access different cultures and perspectives.34. According to the passage, what are some cognitive benefits of being bilingual?A. Enhanced problem-solving skillsB. Improved memory recallC. Increased vocabulary sizeD. Better physical coordination35. How can being bilingual help reduce the risk of neurodegenerative diseases?A. By improving social skillsB. By increasing creativityC. By delaying cognitive declineD. By enhancing problem-solving abilities36. What social and cultural benefits are associated with bilingualism, as mentioned in the passage?A. Increased isolation and exclusionB. Limited communication opportunitiesC. Access to a wider range of people and culturesD. Narrowed perspectives and viewpointsSection IV Writing (30 points)Directions: Write an essay of about 200-300 words on the following topic. You should base your essay on the information given in the outline below.Topic: The Importance of Lifelong LearningOutline:1. Introduction- Definition of lifelong learning- Importance of acquiring new knowledge and skills throughout life2. Benefits of lifelong learning- Personal development and growth- Career advancement and job satisfaction- Improved cognitive function and mental well-being3. Ways to engage in lifelong learning- Formal education programs- Online courses and workshops- Self-study and reading4. Conclusion- Recap of the importance of lifelong learning- Encouragement for individuals to pursue continuous learning opportunitiesRemember to organize your ideas logically and support your essay with relevant examples.The above essay must be structured and written in proper English, demonstrating a clear understanding of the topic and presenting a coherent argument. Good luck with your essay!Overall, the 2024 English exam for the Specialized Undergraduate Program is designed to test your listening, reading, comprehension, and writing skills in English. By preparing thoroughly and practicing consistently, you can improve your performance and achieve success on the exam. Best of luck with your studies and exam preparation!篇32024 National Unified Entrance Examination for Junior College English ExaminationPart I Listening Comprehension (30 points)Section ADirections: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the conversation and the questions will be spoken only once. After each question, there will be a pause. During the pause, you must read the four choices marked A), B), C) and D), and decide which is the best answer. Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.1. A) The man will book a hotel room for the woman.B) The woman will borrow the man's car.C) The man will take the woman to the airport.D) The woman will drive to the airport.2. A) Reading a book.B) Writing an e-mail.C) Watching TV.D) Having dinner.Section BDirections: In this section, you will hear 3 short passages. At the end of each passage, you will hear some questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Passage OneQuestions 11 to 13 are based on the passage you have just heard.11. A) It's 20 dollars.B) It's 21 dollars.C) It's 19 dollars.D) It's 18 dollars.12. A) Take the elevator to the 10th floor.B) Walk straight ahead and take the elevator to the 8th floor.C) Take the stairs to the 8th floor.D) Walk straight ahead and take the elevator to the 10th floor.13. A) He is a journalist.B) He is an engineer.C) He is a taxi driver.D) He is a tour guide.Passage TwoQuestions 14 to 16 are based on the passage you have just heard.14. A) To review what they learned.B) To review what they missed.C) To learn history.D) To know if they can miss class.15. A) Because they can't pay much.B) Because it's too difficult for them.C) Because they don't have time to study.D) Because they don't see the point of it.16. A) Studying the history of American economics.B) American political economy.C) Where to put the roots of democratic society.D) The political economy of America.Passage ThreeQuestions 17 to 20 are based on the passage you have just heard.17. A) 18-month-old.B) 21-month-old.C) 24-month-old.D) 27-month-old.18. A) Everywhere.B) In a small space.C) In a large space.D) At a desk.19. A) 4000 vocabulary words.B) 3000 vocabulary words.C) More than 3000 vocabulary words.D) At least 3000 vocabulary words.20. A) Parents.B) Teachers.C) Other children.D) Everybody.Part II Reading Comprehension (40 points)Section ADirections: In this section, there is a passage with ten questions or incomplete statements. Read the passage carefully. Then answer the questions or complete the statements in the fewest possible words (not exceeding 10 words). Mark your answers on Answer Sheet 1.2019 research study discussed work-life balance ___women aged 25-54.Are American women feeling the challenging feelings?The study explains that women may struggle due to ____family responsibilities.Parents are given more _____ than non-parents.The study found the majority result _______ about achieving a balance.A balance requires personal strategies as well as _____ strategies.Flexible work hours and ____ are linked to work-life balance.The study recommends increasing fair _____ and flexibility.In the extension of family benefits to all employed, the balance requires the employer to _____.Women are advised to prioritize activities that would bring ___.Sleep, not leisure, ______ the stress levels of the subjects.The author's suggestion for helping women is to ______.Section BDirections: In this section, there are four passages. Each passage is followed by several questions or unfinished statements. For each of them, there are four choices marked A), B), C) and D). Choose the one that fits best according to the information in the passage you have just read. Mark your answers on Answer Sheet 1.Passage OneQuestions 21 to 25 are based on the passage you have just heard.21. According to the passage, what product is in high demand?A) white sugarB) organic foodC) soft drinksD) vegetables and soybeans22. What is a new development in the food market?A) Only the wealthy can afford organic food.B) Traditional food is becoming less popular.C) The market for natural food is growing rapidly.D) Supermarkets are selling less organic food.23. Why are consumers buying organic food?A) for the low priceB) for the improved qualityC) for the fresh tasteD) for the popular brands24. What has a big influence on consumers' choices?A) the size of the food marketB) the origin of the productsC) the price of the foodD) the quality of the products25. What can consumers find in supermarkets now?A) less sugarB) less plastic packagingC) more unnatural ingredientsD) more organic products......(To be continued)。

生态系统韧性提升应对气候变化的能力英语作文

生态系统韧性提升应对气候变化的能力英语作文

生态系统韧性提升应对气候变化的能力英语作文Title: Enhancing Ecosystem Resilience to Combat Climate ChangeIn the face of the unprecedented challenges posed by climate change, the resilience of our ecosystems has emerged as a vital defense mechanism. Ecosystem resilience refers to the capacity of natural systems to absorb disturbances, maintain their essential functions, and adapt to new conditions without losing their overall structure and identity. Strengthening this resilience is imperative for mitigating the impacts of climate change and ensuring a sustainable future for all life on Earth.Ecosystems as BuffersEcosystems, from coral reefs to forests and wetlands, act as natural buffers against extreme weather events, droughts, floods, and sea-level rise. Their intricate webs of life support biodiversity, regulate water cycles, sequester carbon, and purify air and water. By enhancing their resilience, we fortify these natural barriers, reducing the severity of climate-related disasters and safeguarding human well-being.Restoration and ConservationRestoring degraded ecosystems and conserving intact ones are cornerstone strategies for boosting resilience. This involves reforestation to increase carbon sequestration, restoring wetlands to manage water flows, and protecting coral reefs to maintain marine biodiversity. Conservation efforts also encompass safeguarding habitats critical for species migration and adaptation, ensuring ecological connectivity across landscapes.Adaptive ManagementAdaptive management is a flexible approach that incorporates learning from ecosystem responses to guide future interventions. By continuously monitoring ecosystem health and adjusting management strategies based on new data, we can better anticipate and address the evolving challenges of climate change. This proactive approach fosters resilience by enabling ecosystems to adapt and thrive in a changing environment.Community EngagementEmpowering local communities to participate in ecosystem managementis crucial. Community-led conservation efforts foster a sense of ownership and responsibility, leading to more sustainable practices. These initiatives often integrate traditional knowledge with modern science, enhancing resilience by leveraging the collective wisdom of those most intimately connected to the land and sea.Policy SupportStrong policies and international agreements are essential to scaling up resilience-building efforts. Governments must prioritize investments in ecosystem restoration, conservation, and climate adaptation. International cooperation is vital, as climate change is a global challenge requiring coordinated responses. By aligning policies and sharing best practices, nations can work together to enhance ecosystem resilience and mitigate climate risks.ConclusionEnhancing ecosystem resilience is a fundamental strategy for combating climate change and securing a resilient future. By restoring and conserving ecosystems, adopting adaptive management, engaging communities, and supporting policy frameworks, we can fortify nature'sdefenses and pave the way for a more sustainable planet. As we face the ongoing threat of climate change, nurturing the resilience of our ecosystems is not just an option; it is a necessity.Translation:标题：增强生态系统抵御气候变化的能力面对气候变化带来的前所未有的挑战，我们生态系统的复原力已成为一种重要的防御机制。