Estimating economic effects of changes in climate and water availability

Social, economic, and environmental systems can be vulnerable to disruptions in water supplies that are likely to accompany future climate changes. Coupled with the challenges of tightening environmental regulations, population growth, economic development and fiscal constraints water supply systems are being pushed beyond the limits of their design and capacity for maintenance. In this paper we briefly review key economic concepts, various economic measures and metrics, and methods to estimate the economic effects on water resources from water supply changes that could accompany climate change. We survey some of the recent empirical literature that focuses on estimates developed for U.S. watersheds at both national and regional scales. Reported estimates of potential damage and loss associated with climate and water supply changes that we observe are significant, though often the metrics vary and make valid and consistent direct cross-comparisons difficult. Whether in terms of changes in GDP or in terms of estimated changes in economic welfare based on associated changes in economic costs and benefits, both national and regional estimates suggest that governments and organizations incorporate prudent steps to assess vulnerabilities to plausible future water supply and demand scenarios and develop responsive adaptation strategies.     

The role of evapotranspiration in climate

Summary A knowledge of the moisture balance at the earth's surface is essential to an understanding of climate. Precipitation and its areal distribution have been investigated in much detail. Evapotranspiration, which is the reverse of precipitation and represents the combined evaporation from the soil surface and transpiration from plants, is little understood and seldom measured. Actual evapotranspiration depends on climatic factors but is limited by the amount of available moisture in the soil. On the other hand, potential evapotranspiration which may be defined as the amount of water which would be lost from a surface completely covered with vegetation if there is sufficient water in the soil at all times for the use of the vegetation depends on climate alone.In order to evaluate the moisture factor in climate, the moisture supply or the precipitation must be compared with the water need or the potential evapotranspiration. The distribution of precipitation through the year never coincides with, and seldom parallels, the distribution of potential evapotranspiration. When the precipitation is in excess of need, the surplus goes to recharge ground water and produce runoff. When the precipitation does not equal the need, there is a deficiency which results in drought.There are various methods of measuring evapotranspiration, all of which are subject to many limitations, and only two of which give promise of yielding acceptable results. The first of these, the so called vapor transfer method, is of especial interest because it is the only one in which measurements may be made of a natural surface without disturbing it in any way. It is not yet a practical method because it requires greater precision in instrumentation than is feasible at present. The second, utilizing a soil tank or evapotranspirometer, is more artificial but it can provide reasonable results if used with care. The evapotranspirometer consists of a sunken open topped tank filled to ground level with soil on which vegetation is planted. A permanent water table is maintained in the soil at a given depth. A large area surrounding the tank must have a vegetation cover the same as in the tank. In addition, soil moisture both inside and outside the tanks must be maintained at the same level. The evapotranspirometer has proven to be a useful and inexpensive instrument for measuring potential evapotranspiration. Soil tank evapotranspirometers have been installed in thirteen localities during the last few years.Pending further theoretical work on the problem of evapotranspiration and the accumulation of observations an empirical formula was devised from data of irrigation projects and watersheds to give the potential evapotranspiration from climatological data alone. The formula has been applied with considerable success by investigators in various parts of the world.The relation between potential evapotranspiration and precipitation at nine European stations is discussed (see fig. 6). Potential evapotranspiration follows a uniform pattern through the year in most of Europe. It is negligible in the winter months as far south as central France, northern Italy, and southern Russia and reaches only 3 cm a month in southern Spain. It rises to a maximum in July that ranges from 10 cm in northern Scandinavia to 17 cm in southern Europe. Precipitation, on the other hand, is highly variable from one region to another. In southeastern Europe it is low, resulting in a large summer water deficiency (56.9 cm at Athens, Greece). This deficiency exists in the summertime over most of the rest of Europe, with the exception of certain restricted regions such as around Zurich, Switzerland. Over western Europe where the precipitation is greater and more uniform through the year the summer water deficiency is smaller. It is 10.6 cm at Birmingham, England and only 2.1 cm at Vard, Norway. In times of excess rainfall water is stored in the soil. The part of this water that is within reach of roots is used before the plants begin to suffer. From studies in western United States it was found that under ordinary circumstances the amount of water stored in the root zone that is available to plants is equivalent to 10 cm of rainfall.The uses as well as the limitations of potential evapotranspiration are only partially known. Even with its present limited use in climatology, hydrology, agriculture, and soil tractionability, it has shown itself to be a powerful tool. With more information concerning the nature of potential evapotranspiration and knowledge of its areal distribution from the tropics to the arctic, its usefulness should increase manifold.

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Zusammenfassung Die Kenntnis der Feuchtigkeitsbilanz an der Erdoberfläche ist für das Verständnis des Klimas unentbehrlich. Der Niederschlag und seine räumliche Verteilung sind in allen Einzelheiten untersucht. Evapotranspiration dagegen, die das Zusammenwirken der Verdunstung von der Erdoberfläche und der Transpiration von den Pflanzen und somit gleichzeitig das Gegenstück zum Niederschlag darstellt, ist wenig bekannt und nur selten untersucht. Die tatsächliche Evapotranspiration hängt von Klimafaktoren ab, ist jedoch durch die Menge der verfügbaren Bodenfeuchtigkeit begrenzt. Anderseits hängt die potentielle Evapotranspiration nur vom Klima allein ab, da sie durch die Wassermenge definiert ist, die von einer vollständig mit Vegetation bedeckten Fläche abgegeben wird, falls für den Bedarf der Vegetation ständig genügend Wasser zur Verfügung steht.Um den Feuchtigkeitsfaktor im Klima zu untersuchen, muß die Feuchtigkeitszufuhr durch Niederschlag mit dem Wasserbedarf oder der potentiellen Evapotranspiration verglichen werden. Die Niederschlagsverteilung über das Jahr deckt sich kaum je mit dem Verlauf der potentiellen Evapotranspiration. Wenn der Niederschlag den Bedarf übersteigt, wird der Überschuß zur Speicherung der Grundwasserreserven und zur Steigerung des Abflusses verwendet; bleibt jedoch der Niederschlag hinter dem Bedarf zurück, so entsteht ein Defizit, das zu Dürre führt.Zur Messung der Evapotranspiration bestehen verschiedene Methoden; diese unterliegen durchwegs gewissen Einschränkungen und nur zwei davon lassen annehmbare Resultate erwarten. Die eine der beiden, die sogenannte Dampfaustauschmethode bietet besonderes Interesse, da sie allein auf Messungen an einer natürlichen Fläche ohne Störungsursachen beruht; doch ist sie noch nicht in der Praxis verwendbar, da sie größere instrumentelle Präzision erfordert, als zur Zeit erreichbar ist. Die zweite Methode, bei der ein Gefäß im Boden (Evapotranspirometer) verwendet wird, arbeitet stärker mit künstlichen Bedingungen, kann jedoch bei sorgfältiger Anwendung vernünftige Resultate liefern. Das Evapotranspirometer besteht aus einem versenkten, oben offenen Gefäß, das bis zum Erdbodenniveau mit Erde gefüllt ist, auf der Vegetation gepflanzt wird; ein konstanter Wasserspiegel wird im Boden in bestimmter Höhe gehalten. Die weitere Umgebung des Gefäßes muß dieselbe Vegetationsdecke haben wie das Gefäß selbst. Zudem muß die Bodenfeuchtigkeit innerhalb und außerhalb des Evapotranspirometers auf gleicher Höhe gehalten werden. Das Gerät hat sich als nützliches und billiges Instrument zur Messung der potentiellen Evapotranspiration erwiesen. In den letzten Jahren wurden solche Bodengefäßevapotranspirometer (insgesamt 13) an verschiedenen Orten installiertVorgängig weiterer theoretischer Untersuchungen über das Problem der Evapotranspiration und der Sammlung von Beobachtungsmaterial wurde auf Grund von Erfahrungen an Bewässerungsanlagen eine empirische Formel zur Bestimmung der Evapotranspiration aus klimatologischen Daten aufgestellt; diese Formel wurde in verschiedenen Teilen der Erde mit gutem Erfolg angewandt.Die potentielle Evapotranspiration an neun europäischen Stationen besitzt im allgemeinen einen einheitlichen Jahresverlauf mit sehr kleinen Werten im Winter und einem Maximum im Juli. Anderseits zeigt der Niederschlag große Unterschiede zwischen den einzelnen Gegenden. Während er in Südosteuropa bei gro\em Sommerdefizit gering ist, erreicht er in Westeuropa größere Mengen. In Zeiten von Überschuß wird Regenwasser im Boden gespeichert; soweit sich dieses Wasser in der Reichweite der Wurzeln befindet, wird es ausgenützt, bevor die Pflanzen zu welken beginnen. Bei Untersuchungen in den westlichen Vereinigten Staaten wurde festgestellt, daß unter gewöhnlichen Bedingungen die im Wurzelbereich gespeicherte Wassermenge, die den Pflanzen zur Verfügung steht, einer Niederschlagsmenge von 10 cm entspricht.Die Verwendungsmöglichkeiten wie auch die Grenzen der potentiellen Evapotranspiration sind erst teilweise bekannt; aber auch mit ihrer gegenwärtigen beschränkten Anwendung in Klimatologie, Hydrologie, Landwirtschaft und Bodenbearbeitung hat sie sich schon als wertvolles Hilfsmittel erwiesen. Mit zunehmenden Kenntnissen über die Eigenschaften der potentiellen Evapotranspiration und über ihre geographische Verteilung von den Tropen bis zu den Polargebieten dürfte ihre Bedeutung stark anwachsen.

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Résumé Pour comprendre le climat il est indispensable de connaître le bilan de l'humidité de la surface de la terre. Si les précipitations et leur distribution géographique ont été étudiées dans tous leurs détails, l'évapotranspiration par contre, qui représente l'effet combiné de l'évaporation de la surface du sol et de la transpiration végétale et forme ainsi la contre-partie des précipitations, est peu connue et n'a fait que rarement l'objet d'études. L'évapotranspiration effective dépend de facteurs climatiques mais est limitée par la quantité disponible d'humidité du sol. D'autre part l'évapotranspiration potentielle ne dépend que du climat puis-qu'elle est définie par la quantité d'eau fournie par une surface entièrement recouverte de végétation au cas où il y a assez d'eau pour subvenir aux besoins de celle-ci.Pour étudier le facteur humidité d'un climat, il faut comparer l'apport humide des précipitations au besoin en eau ou à l'évapotranspiration potentielle. Il est rare que la distribution annuelle des pluies corresponde à la courbe d'évapotranspiration potentielle. Des précipitations excédant le besoins alimentent les réserves d'eau souterraine et accroissent l'écoulement; une pluie inférieure aux besoins crée un déficit conduisant à la sécheresse.Il existe différentes méthodes de mesure de l'évapotranspiration; elles sont toutes insuffisantes et deux d'entre elles seulement permettent d'espérer des résultats acceptables. L'une, appeléemethode d'èchange de vapeur, est particulièrement intéressante parcequ'elle repose sur des mesures sur le terrain sans modifier les conditions naturelles; elle n'est cependant pas applicable en pratique car elle exige une précision instrumentale supérieure à celle que l'on peut atteindre actuellement. L'ature méthode qui se sert d'un récipient, ditevapotranspiromètre, introduit davantage de conditions artificielles; bien appliquée elle fournit cependant des résultats raisonnables. L'évapotranspiromètre est un récipient enterré, ouvert vers le haut et rempli de terre jusqu'au niveau du sol et dans lequel on sème la même végétation qu'aux alentours; on maintient à l'intérieur un niveau d'eau constant. En outre l'humidité du sol doit être la même à l'extérieur et à l'intérieur de l'évapotranspiromètre qui s'est révélécomme un instrument utile et peu coûteux. On a installé ces dernières années treize de ces appareils en différents endroits.Sans attendre de nouvelles recherches théoriques ni la collation de matériel d'observations, on a établi sur la base d'expériences faites dans des installations d'irrigation une formule empirique permettant de déterminer l'évapotranspiration à partir de données climatologiques; cette formule a été utilisée avec succès en différents points du globe.L'évapotranspiration potentielle de neuf stations européennes présente en général une marche annuelle uniforme avec très petites valeurs en hiver et un maximum en juillet. D'autre part les précipitations accusent de grandes différences suivant les régions; tandis que dans le Sud-Est européen elles sont faibles et déficitaires en été, elles sont plus importantes en Europe occidentale. Aux époques d'excédent, l'eau de pluie s'accumule dans le sol; tant que cette eau est à portée des racines, elle est utilisée par les plantes avant que celles-ci ne commencent à se faner. Lors de recherches dans l'Ouest des Etats-Unis, on a constaté que dans les conditions normales l'eau de réserve qui peut atteindre les racines et qui est à disposition des plantes correspond à une pluie de 10 cm.On ne connaît que partiellement aujourd'hui les possibilités d'application et les insuffisances de la notion d'évapotranspiration potentielle; celle-ci s'est cependant révélée utile en climatologie, en hydrologie et en agriculture. Lorsque les propriétés de l'évapotranspiration potentielle et sa distribution géographique des tropiques aux régions polaires seront mieux connues, cette notion verra son importance s'accroître fortement.

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With 6 Figures.

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The material in this paper is adapted in part from previously published papers of the authors. Grateful acknowledgement is made to the Editors of the Geographical Review and the Annals of the Association of American Geographers for permission to reprint brief selections without change.     

Vulnerability of water supply from the Oregon Cascades to changing climate: Linking science to users and policy

Despite improvements in understanding biophysical response to climate change, a better understanding of how such changes will affect societies is still needed. We evaluated effects of climate change on the coupled human-environmental system of the McKenzie River watershed in the Oregon Cascades in order to assess its vulnerability. Published empirical and modeling results indicate that climate change will alter both the timing and quantity of streamflow, but understanding how these changes will impact different water users is essential to facilitate adaptation to changing conditions. In order to better understand the vulnerability of four water use sectors to changing streamflow, we conducted a series of semi-structured interviews with representatives of each sector, in which we presented projected changes in streamflow and asked respondents to assess how changing water availability would impact their activities. In the McKenzie River watershed, there are distinct spatial and temporal patterns associated with sensitivity of water resources to climate change. This research illustrates that the implications of changing streamflow vary substantially among different water users, with vulnerabilities being determined in part by the spatial scale and timing of water use and the flexibility of those uses in time and space. Furthermore, institutions within some sectors were found to be better positioned to effectively respond to changes in water resources associated with climate change, while others have substantial barriers to the flexibility needed to manage for new conditions. A clearer understanding of these opportunities and constraints across water use sectors can provide a basis for improving response capacity and potentially reducing vulnerability to changing water resources in the region.     

Climatology of Precipitation of Different Genesis in Northern Eurasia

A method for discriminating among different types of precipitation is presented. The method is based on surface observations of precipitation, present and past weather, and the morphological types of clouds. The climatology of showery, nonshowery, and drizzle precipitation in Northern Eurasia is studied using the data of 529 Russian weather stations for the period of 1966–2014. Showery precipitation dominates in Northern Eurasia. In general, showery precipitation has greater temporal (monthly and diurnal) and spatial variability than nonshowery precipitation. The majority of showers are registered in summer (the maximum is in July), whereas the high est total monthly nonshowery precipitation is observed in autumn (the maximum is in October). The daily intensity values of showery and nonshowery precipitation are generally close, the maximum intensity is recorded in July–August. For three-hour in tervals, the shower in tensity is by 1.1–1.5 times higher. The drawbacks of the presented methodology are discussed.     

Potential impact of climate change on the water availability of South Saskatchewan River Basin

The potential hydrologic impact of climatic change on three sub-basins of the South Saskatchewan River Basin (SSRB) within Alberta, namely, Oldman, Bow and Red Deer River basins was investigated using the Modified Interactions Soil-Biosphere-Atmosphere (MISBA) land surface scheme of Kerkhoven and Gan (Advances in Water Resources 29:808–826 2006). The European Centre for Mid-range Weather Forecasts global re-analysis (ERA-40) climate data, Digital Elevation Model of the National Water Research Institute, land cover data and a priori soil parameters from the Ecoclimap global data set were used to drive MISBA to simulate the runoff of SSRB. Four SRES scenarios (A21, A1FI, B21 and B11) of four General Circulation Models (CCSRNIES, CGCM2, ECHAM4 and HadCM3) of IPCC were used to adjust climate data of the 1961–1990 base period (climate normal) to study the effect of climate change on SSRB over three 30-year time periods (2010–2039, 2040–2069, 2070–2099). The model results of MISBA forced under various climate change projections of the four GCMs with respect to the 1961–1990 normal show that SSRB is expected to experience a decrease in future streamflow and snow water equivalent, and an earlier onset of spring runoff despite of projected increasing trends in precipitation over the 21st century. Apparently the projected increase in evaporation loss due to a warmer climate over the 21st century will offset the projected precipitation increase, leading to an overall decreasing trend in the basin runoff of SSRB. Finally, a Gamma probability distribution function was fitted to the mean annual maximum flow and mean annual mean flow data simulated for the Oldman, Bow and Red Deer River Basins by MISBA to statistically quantify the possible range of uncertainties associated with SRES climate scenarios projected by the four GCMs selected for this study.     

湖南气候对全球气候变化的响应

利用湖南省96个台站1960—2010年逐日气象观测资料,在进行均一性检验和订正的基础上对湖南省气候变化事实进行检测分析。结果表明:湖南气候与全球气候变化一致,呈现以变暖为主要特征的变化,且变暖存在季节、地域上的差异,冬、春、秋气温变暖趋势显著,增暖幅度最大的区域在湘北地区;对气候变暖响应敏感的要素主要是与平均气温、冬季气温相关密切的要素,如季平均气温、年平均最低气温、活动积温等;湖南气温在突变时间上具有较好的时间逻辑关系;湖南降水量无显著趋势变化,但极端降水增加,地域性差异明显,湖南东部地区降水量呈现明显增加趋势,日降水量大于等于100 mm的日数呈显著增加趋势;湖南日照时数、风速、相对湿度均呈现显著减少的变化趋势。     

Simulating the effects of climate changes on Eastern Eurasia forests

The extensive forests of Eastern Eurasia cover an area of ca. 6 million km². The FAREAST model, a forest gap model that simulates the stand composition and dynamics of Eastern Eurasian forests under the current climate, was used to simulate the responses of the Eastern Eurasia Forests to the climate change. Two different scenarios of possible future climatic change were obtained from the IPCC (2001) report (CMIP2 and IS92a-GS) and were used as input to the FAREAST model to determine the compositional and structural sensitivity to climate changes for several locations and along montane elevation gradients. The simulation results suggest that, under the influence of the conditions in the two climate-change scenarios, the underlying forest dynamics should be quite different. Further, Eastern Eurasian forests maintain currents forest structure and biomass only within a small range of climate change. Broad-leaved deciduous trees of such genera as Fraxinus, Quercus and Tilia increase their ranges over Eastern Eurasia under the climate-change scenarios. Conifers, such as Larix and Picea, decrease sharply under climate change and the area of their distributions are reduced. The overall biomass of Pinus is not decreased over the region. While the Pinus distribution range shifts, the area associated with the range of the taxa is not changed.     

Optimal water depth management on river-fed National Wildlife Refuges in a changing climate

The prairie pothole region (PPR) in the north-central United States and south-central Canada constitutes the most important waterfowl breeding area in North America. Projected long-term changes in precipitation and temperature may alter the drivers of waterfowl abundance: wetland availability and emergent vegetation cover. Previous studies have focused on isolated wetland dynamics, but the implications of changing precipitation on managed, river-fed wetlands have not been addressed. Using a structured decision making (SDM) approach, we derived optimal water management actions for 20 years at four river-fed National Wildlife Refuges (NWRs) in North and South Dakota under contrasting increasing/decreasing (+/?0.4 %/year) inflow scenarios derived from empirical trends. Refuge pool depth is manipulated by control structures. Optimal management involves setting control structure heights that have the highest probability of providing a desired mix of waterfowl habitat, given refuge capacities and inflows. We found optimal seasonal control structure heights for each refuge were essentially the same under increasing and decreasing inflow trends of 0.4 %/year over the next 20 years. Results suggest managed pools in the NWRs receive large inflows relative to their capacities. Hence, water availability does not constrain management; pool bathymetry and management tactics can be greater constraints on attaining management objectives than climate-mediated inflow. We present time-dependent optimal seasonal control structure heights for each refuge, which are resilient to the non-stationary precipitation scenarios we examined. Managers can use this information to provide a desired mixture of wildlife habitats, and to re-assess management objectives in reserves where pool bathymetry prevents attaining the currently stated objectives.     

A new assessment of climate change impacts on food production shortfalls and water availability in Russia

While previous studies have focused on impacts of average climate change on Russian agriculture and water resources, this study takes into account the impact of changing frequency and spatial heterogeneity of extreme climate events, and the reliance of most of Russia on a few food producing regions. We analyze impacts of the IPCC A2 and B2 climate scenarios with the use of the Global Assessment of Security (GLASS) model (containing the Global Agro-Ecological Zones (GAEZ) crop production model and the Water-Global Assessment and Prognosis (WaterGAP 2) water resources model). As in previous studies we find that decreased crop production in some Russian regions can be compensated by increased production in others resulting in relatively small average changes. However, a different perspective on future risk to agriculture is gained by taking into account a change in frequency of extreme climate events. Under climate normal conditions it is estimated that “food production shortfalls” (a year in which potential production of the most important crops in a region is below 50% of its average climate normal production, taking into account production in food-exporting regions) occur roughly 1–3 years in each decade. This frequency will double in many of the main crop growing areas in the 2020s, and triple in the 2070s. The effects of these shortfalls are likely to propagate throughout Russia because of the higher likelihood of shortfalls occurring in many crop export regions in the same year, and because of the dependence of most Russian regions on food imports from a relatively few main crop growing regions. We estimate that approximately 50 million people currently live in regions that experience one or more shortfalls each decade. This number may grow to 82–139 million in the 2070s. The assessment of climate impacts on water resources indicates an increase in average water availability in Russia, but also a significantly increased frequency of high runoff events in much of central Russia, and more frequent low runoff events in the already dry crop growing regions in the South. These results suggest that the increasing frequency of extreme climate events will pose an increasing threat to the security of Russia's food system and water resources.     

Transient climate response to changing carbon dioxide concentration

The time-dependent response of climate changes to changing atmospheric concentration of carbon dioxide is modeled using an energy balance atmospheric model coupled to a one-dimensional upwelling diffusion model of the deep ocean. Such a model introduces time delays so that the calculated globally-averaged temperature lags that which would be predicted by assuming radiative equilibrium. The climate model is coupled to a simple carbon cycle model and a ‘social’ model that simulates decreasing emission in response to increasing global temperatures. The thermal inertia of the system is such that temperatures continue to increase after carbon dioxide concentrations are decreasing. Consultant to BNL from New York University. Semester Student, Fall 1979, Alcorn State College. This research was performed under the auspices of the United States Department of Energy under Contract No. DE-AC02-76CH00016. By acceptance of this article, the publisher and/or recipient acknowledges the U.S. Government’s right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.     

IPCC AR6报告解读：短寿命气候强迫因子的气候及环境效应

影响气候变化的大气成分,依据其在大气中存留的时间,分为长寿命的温室气体和短寿命的气候强迫因子（SLCFs)。考虑到SLCFs在气候变化和大气环境中的重要作用,IPCC第六次评估报告（AR6）首次有了专门针对SLCFs的章节（第六章)。本文解读IPCC报告关于SLCFs的主要结论,特别强调AR5以来的最新结论,包括：SLCFs的定义、SLCFs排放和大气含量的变化特征及其对辐射强迫和全球气候的影响、不同共享社会经济路径（SSP）情景下SLCFs对未来气候变化和空气质量可能的影响,以及COVID-19疫情期间减排对气候变化的影响。文末也讨论了结论的不确定性以及结论对我国的启示。     

欧亚大陆季节增（融）雪盖面积变化特征分析

利用美国冰雪资料中心(National Snow and Ice Data Center)提供的近40年逐周的卫星反演雪盖资料,定义了各季节新增(融化)雪盖而积指数(fresh snow extent),即增/融雪覆盖率P_(FSE)、增/融雪面积A_(FSE)、欧亚大陆北部增/融雪面积之和T_(FSE),针对欧亚大陆各季节平均的雪盖面积本身(snow extent,P_(SE)、A_(SE)、T_(SE)和其增(融)雪盖面积,分析比较二者的变化特征.结果表明,欧亚大陆各季节平均的雪盖面积和相应增(融)雪盖面积不论是气候态分布还是其年际、十年际变化均有明显不同,其中以冬、春季差别更为明显;夏、秋季二者虽有较好的一致性,但增(融)雪盖面积的变率明显强于雪盖而积本身;另外,冬季欧洲新增雪盖对欧业北部冬季雪盖面积以及其后的春季雪盖都有较显著的影响,而春季欧洲和中纬度亚洲地区的融雪则受到冬、春两季雪盖情况的影响.进一步分析欧亚大陆冬、春两季增(融)雪盖与ENSO关系显示,二者除在个别地区(两伯利业北部、欧洲中东部以及青藏高原)存在较明显关系外,整体上,欧亚大陆北部雪盖变化既不受控于ENSO,也不会显著影响ENSO.     

气候变化、植被改变及人类用水与黄河流域水循环的研究进展

受气候增暖和人类活动的双重影响,黄河流域的水循环正在发生显著变化,水资源供需矛盾突出。陆地水循环是一个复杂的非线性系统,为清晰认识水循环变化的全貌,并合理高效利用有限的水资源量,需要综合考虑水循环各个要素之间的协同变化机制。同时,在“人类世”背景下,黄河流域水循环研究必须考虑人类活动的影响,主要包括植被变化和人类用水,其中人类用水主体为农业灌溉。自从实施生态恢复工程以来,黄土高原植被覆盖明显改善的同时也引发了对径流、蒸散发、降水、土壤湿度以及地下水的一系列影响,且研究结论还存在一些争议,但黄土高原植被覆盖改善使得该地区蒸散发量增加基本达成共识,大多数研究支持植被改善减少径流的结论。黄河流域的农业灌溉方式主要为大水漫灌,其对地表蒸散发、地表水及地下水多个过程具有重要影响。本文主要针对黄河流域的水循环研究,讨论相关研究进展以及发展方向。     

Evolution of the Parisian urban climate under a global changing climate

The evolution of the Parisian urban climate under a changing climate is analyzed from long-term offline numerical integrations including a specific urban parameterization. This system is forced by meteorological conditions based on present-climate reanalyses (1970–2007), and climate projections (2071–2099) provided by global climate model simulations following two emission scenarios (A1B and A2). This study aims at quantifying the impact of climate change on air temperature within the city and in the surroundings. A systematic increase of 2-meter air temperature is found. In average according to the two scenarios, it reaches +?2.0/2.4°C in winter and +?3.5/5.0°C in summer for the minimum and maximum daily temperatures, respectively. During summer, the warming trend is more pronounced in the surrounding countryside than in Paris and suburbs due to the soil dryness. As a result, a substantial decrease of the strong urban heat islands is noted at nighttime, and numerous events with negative urban heat islands appear at daytime. Finally, a 30% decrease of the heating degree days is quantified in winter between present and future climates. Inversely, the summertime cooling degree days significantly increase in future climate whereas they are negligible in present climate. However, in terms of accumulated degree days, the increase of the demand in cooling remains smaller than the decrease of the demand in heating.     

Sensitivity of evapotranspiration of cotton and sorghum in west Texas to changes in climate and CO2

Summary In regions such as west Texas where water is scarce, changes in the water balance may have a significant impact on agricultural production and management of water resources. We used the mechanistic soil-plant-atmosphere simulation model ENWATBAL to evaluate changes in soil water evaporation (E) and transpiration (T) in cotton and grain sorghum that may occur due to climate change and elevated CO₂ in west Texas. Climatic and plant factors were varied individually, and in combination, to determine their impact onE andT. Of the climatic factors,E was most sensitive to changes in vapor pressure, andT to changes in irradiance. Simulations suggest that if warming is accompanied by higher humidity, the impact of climate change may be minimal. However, if the climate becomes warmer and less humid,ET may increase substantially. Simulations also suggest that enhanced growth due to elevated CO₂ may have a greater impact onET than climatic change.With 9 Figures     

Future cereal production in China: The interaction of climate change,water availability and socio-economic scenarios

Food production in China is a fundamental component of the national economy and driver of agricultural policy. Sustaining and increasing output to meet growing demand faces significant challenges including climate change, increasing population, agricultural land loss and competing demands for water. Recent warming in China is projected to accelerate by climate models with associated changes in precipitation and frequency of extreme events. How changes in cereal production and water availability due to climate change will interact with other socio-economic pressures is poorly understood. By linking crop and water simulation models and two scenarios of climate (derived from the Regional Climate Model PRECIS) and socio-economic change (downscaled from IPCC SRES A2 and B2) we demonstrate that by the 2040s the absolute effects of climate change are relatively modest. The interactive effects of other drivers are negative, leading to decreases in total production of ?18% (A2) and ?9% (B2). Outcomes are highly dependent on climate scenario, socio-economic development pathway and the effects of CO₂ fertilization on crop yields which may almost totally offset the decreases in production. We find that water availability plays a significant limiting role on future cereal production, due to the combined effects of higher crop water requirements (due to climate change) and increasing demand for non-agricultural use of water (due to socio-economic development). Without adaptation, per capita cereal production falls in all cases, by up to 40% of the current baseline.By simulating the effects of three adaptation scenarios we show that for these future scenarios China is able to maintain per capita cereal production, given reasonable assumptions about policies on land and water management and progress in agricultural technology. Our results are optimistic because PRECIS simulates much wetter conditions than a multi-model average, the CO₂ crop yield response function is highly uncertain and the effects of extreme events on crop growth and water availability are likely to be underestimated.     

Interrelation of the intraseasonal precipitation variability over Eurasia to the Eliassen-Palm flux characteristics over the Northern Hemisphere

Conditional averages of principal components of the Eliassen-Palm flux divergence variability are projected onto the daily precipitation amounts chart. The conditions of calculating the average values are determined by the dates classified in three equiprobable precipitation categories. The classification and calculation of characteristics are performed for the summer and winter seasons. Using the rotated principal component analysis, several regions are revealed of statistically significant interrelation between extreme precipitation and the first EP flux divergence variability modes, a simplified exploratory interpretation of interrelations is given and several recommendations are formulated for correcting seasonal forecasts of meteorological conditions with the use of results obtained.