Impact of the North Atlantic Oscillation on Middle Eastern Climate and Streamflow   总被引：6，自引：0，他引：6  

Heidi M. Cullen  Alexey Kaplan  Phillip A. Arkin  Peter B. deMenocal 《Climatic change》2002,55(3):315-338

Interannual to decadal variations in Middle Eastern temperature, precipitationand streamflow reflect the far-field influence of the North Atlantic Oscillation (NAO), a dominant mode of Atlantic sector climate variability. Using a new sea surface temperature (SST) based index of the NAO and availablestreamflow data from five Middle Eastern rivers, we show that the first principal component of December through March streamflow variability reflects changes in the NAO. However, Middle East rivers have two primary flooding periods.The first is rainfall-driven runoff from December through March, regulated on interannual to decadal timescales by the NAO as reflected in local precipitation and temperature.The second period, from April through June, reflects spring snowmelt and contributes in excess of 50% of annual runoff.This period, known locally as the khamsin, displays no significantNAO connections and a less direct relationship with local climatic factors, suggesting that streamflow variability during this period reflects land-cover change, possibly related to agriculture and hydropower generation, and snowmelt.  相似文献   

Climate change impacts on U.S. Coastal and Marine Ecosystems   总被引：1，自引：0，他引：1  

Donald Scavia  John C. Field  Donald F. Boesch  Robert W. Buddemeier  Virginia Burkett  Daniel R. Cayan  Michael Fogarty  Mark A. Harwell  Robert W. Howarth  Curt Mason  Denise J. Reed  Thomas C. Royer  Asbury H. Sallenger  James G. Titus 《Estuaries and Coasts》2002,25(2):149-164

Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO₂. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO₂ levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences.  相似文献   

Scaling effects on modeled surface energy-balance components using the NOAH-OSU land surface model   总被引：3，自引：0，他引：3  

V. Sridhar  Ronald L. Elliott  Fei Chen 《Journal of Hydrology》2003,280(1-4):105-123

As surface exchange processes are highly non-linear and heterogeneous in space and time, it is important to know the appropriate scale for the reasonable prediction of these exchange processes. For example, the explicit representation of surface variability has been vital in predicting mesoscale weather events such as late-afternoon thunderstorms initiated by latent heat exchanges in mid-latitude regions of the continental United States. This study was undertaken to examine the effects of different spatial scales of input data on modeled fluxes, so as to better understand the resolution needed for accurate modeling. A statistical procedure was followed to select two cells from the Southern Great Plains 1997 hydrology experiment region, each 20 km×20 km, representing the most homogeneous and the most heterogeneous surface conditions (based on soil and vegetation) within the study region. The NOAH-OSU (Oregon State University) Land Surface Model (LSM) was employed to estimate surface energy fluxes. Three scales of study (200 m, 2 and 20 km) were considered in order to investigate the impacts of the aggregation of input data, especially soil and vegetation inputs, on the model output. Model results of net radiation and latent, sensible and ground heat fluxes were compared for the three scales. For the heterogeneous area, the model output at the 20-km resolution showed some differences when compared with the 200-m and 2-km resolutions. This was more pronounced in latent heat (12% decrease), sensible heat (22% increase), and ground heat flux (44% increase) estimation than in net radiation. The scaling effects were much less for the relatively homogeneous land area with 5% increase in sensible heat and 4% decrease in ground heat flux estimation. All of the model outputs for the 2- and 20-km resolutions were in close agreement. The results suggested that, for this study region, soils and vegetation input resolution of about 2 km should be chosen for realistic modeling of surface exchange processes. This resolution was sufficient to capture the effects of sub-grid scale heterogeneity, while avoiding the data and computational difficulties associated with higher spatial resolutions.  相似文献   

A statistical approach to evaluating distance metrics and analog assignments for pollen records     

Daniel G. Gavin  W. Wyatt Oswald  Eugene R. Wahl  John W. Williams 《Quaternary Research》2003,60(3):356-367

The modern analog technique typically uses a distance metric to determine the dissimilarity between fossil and modern biological assemblages. Despite this quantitative approach, interpretation of distance metrics is usually qualitative and rules for selection of analogs tend to be ad hoc. We present a statistical tool, the receiver operating characteristic (ROC) curve, which provides a framework for identifying analogs from distance metrics. If modern assemblages are placed into groups (e.g., biomes), this method can (1) evaluate the ability of different distance metrics to distinguish among groups, (2) objectively identify thresholds of the distance metric for determining analogs, and (3) compute a likelihood ratio and a Bayesian probability that a modern group is an analog for an unknown (fossil) assemblage. Applied to a set of 1689 modern pollen assemblages from eastern North America classified into eight biomes, ROC analysis confirmed that the squared-chord distance (SCD) outperforms most other distance metrics. The optimal threshold increased when more dissimilar biomes were compared. The probability of an analog vs no-analog result (a likelihood ratio) increased sharply when SCD decreased below the optimal threshold, indicating a nonlinear relationship between SCD and the probability of analog. Probabilities of analog computed for a postglacial pollen record at Tannersville Bog (Pennsylvania, USA) identified transitions between biomes and periods of no analog.  相似文献   

The Influence of Vegetation Cover on Summer Precipitation in China： a Statistical Analysis of NDVI and Climate Data   总被引：18，自引：0，他引：18  

ZHANG Jingyong  DONG Wenjie  FU Congbin  WU Lingyun 《大气科学进展》2003,20(6):1002-1006

This study provides new evidence for the feedback effects of vegetation cover on summer precipitation in different regions of China by calculating immediate (same season), and one-and two-season lagged correlations between the normalized difference vegetation index (NDVI) and summer precipitation. The results show that the correlation coefficients between NDVI in spring and the previous winter and precipitation in summer are positive in most regions of China, and they show significant difference between regions. The stronger one-and two-season lagged correlations occur in the eastern arid/semi-arid region, Central China,and Southwest China out of the eight climatic regions of China, and this implies that vegetation cover change has more sensitive feedback effects on summer precipitation in the three regions. The three regions are defined as sensitive regions. Spatial analyses of correlations between spring NDVI averaged over each sensitive region and summer precipitation of 160 stations suggest that the vegetation cover strongly affects summer precipitation not only over the sensitive region itself but also over other regions, especially the downstream region.  相似文献   

黄海、东海海域出海气旋发展过程中尺度数值模拟   总被引：1，自引：0，他引：1       下载免费PDF全文

周明煜  Hsiaoming Hsu  袁耀初 《地球物理学报》2003,46(2):175-178

利用MM5中尺度模式对1999年6月两个出海气旋发展过程进行 数值模拟. 数值模拟的气旋出海后移动路径与实际情况基本一致. 在数值模拟基础上重点讨 论了出海气旋发展过程潜热通量和感热通量的分布及其演变情况. 气旋出海后在气旋中心区 南方和东方存在负潜热通量和感热通量区. 出海气旋的东移和发展，其前方强大正热通量区 的存在可能是重要原因之一.  相似文献   

Understanding Climatic Impacts, Vulnerabilities, and Adaptation in the United States: Building a Capacity for Assessment     

Edward A. Parson  Robert W. Corell  Eric J. Barron  Virginia Burkett  Anthony Janetos  Linda Joyce  Thomas R. Karl  Michael C. MacCracken  Jerry Melillo  M. Granger Morgan  David S. Schimel  Thomas Wilbanks 《Climatic change》2003,57(1-2):9-42

Based on the experience of the U.S. National Assessment, we propose a program of research and analysis to advance capability for assessment of climate impacts, vulnerabilities, and adaptation options. We identify specific priorities for scientific research on the responses of ecological and socioeconomic systems to climate and other stresses; for improvement in the climatic inputs to impact assessments; and for further development of assessment methods to improve their practical utility to decision-makers. Finally, we propose a new institutional model for assessment, based principally on regional efforts that integrate observations, research, data, applications, and assessment on climate and linked environmental-change issues. The proposed program will require effective collaboration between scientists, resource managers, and other stakeholders, all of whose expertise is needed to define and prioritize key regional issues, characterize relevant uncertainties, and assess potential responses. While both scientifically and organizationally challenging, such an integrated program holds the best promise of advancing our capacity to manage resources and the economy adaptively under a changing climate.  相似文献   

The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy   总被引：4，自引：0，他引：4  

Gregg Marland  Roger A. Pielke Sr. 《Climate Policy》2003,3(2):149-157

Strategies to mitigate anthropogenic climate change recognize that carbon sequestration in the terrestrial biosphere can reduce the build-up of carbon dioxide in the Earth’s atmosphere. However, climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in terrestrial vegetation and to work toward a better understanding of the full climate system. Acknowledging the importance of land surface change as a component of climate change makes it more challenging to create a system of credits and debits wherein emission or sequestration of carbon in the biosphere is equated with emission of carbon from fossil fuels. Recognition of the complexity of human-caused changes in climate does not, however, weaken the importance of actions that would seek to minimize our disturbance of the Earth’s environmental system and that would reduce societal and ecological vulnerability to environmental change and variability.  相似文献   

TransCom 3 CO₂ inversion intercomparison: 1. Annual mean control results and sensitivity to transport and prior flux information     

KEVIN ROBERT GURNEY  RACHEL M. LAW  A. SCOTT DENNING  PETER J. RAYNER  DAVID BAKER  PHILIPPE BOUSQUET  LORI BRUHWILER  YU-HAN CHEN  PHILIPPE CIAIS  SONGMIAO FAN  INEZ Y. FUNG  MANUEL GLOOR  MARTIN HEIMANN  KAZ HIGUCHI  JASMIN JOHN  EVA KOWALCZYK  TAKASHI MAKI  SHAMIL MAKSYUTOV  PHILIPPE PEYLIN  MICHAEL PRATHER  BERNARD C. PAK  JORGE SARMIENTO  SHOICHI TAGUCHI  TARO TAKAHASHI  CHIU-WAI YUEN 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):555-579

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Effects of Land Use on the Climate of the United States   总被引：14，自引：0，他引：14  

Gordon B. Bonan 《Climatic change》1997,37(3):449-486

Land use practices have replaced much of the natural needleleaf evergreen, broadleaf deciduous, and mixed forests of the Eastern United States with crops. To a lesser extent, the natural grasslands in the Central United States have also been replaced with crops. Simulations with a land surface process model coupled to an atmospheric general circulation model show that the climate of the United States with modern vegetation is significantly different from that with natural vegetation. Three important climate signals caused by modern vegetation are: (1) 1 °C cooling over the Eastern United States and 1 °C warming over the Western United States in spring; (2) summer cooling of up to 2 °C over a wide region of the Central United States; and (3) moistening of the near-surface atmosphere by 0.5 to 1.5 g kg^-1over much of the United States in spring and summer. Although individual months show large, statistically significant differences in precipitation due to land-use practices, these differences average out over the course of the 3-month seasons. These changes in surface temperature and moisture extend well into the atmosphere, up to 500 mb, and affect the boundary layer and atmospheric circulation. The altered climate is due to reduced surface roughness, reduced leaf and stem area index, reduced stomatal resistance, and increased surface albedo with modern vegetation compared to natural vegetation. The climate change caused by land use practices is comparable to other well known anthropogenic climate forcings. For example, it would take 100 to 175 years at the current, observed rate of summer warming over the United States to offset the cooling from deforestation. The summer sulfate aerosol forcing completely offsets the greenhouse forcing over the Eastern United States. Similarly, the climatic effect of North American deforestation, with extensive summer cooling, further offsets the greenhouse forcing.  相似文献