Simulating the response of a closed‐basin lake to recent climate changes in tropical West Africa (Lake Bosumtwi,Ghana)     

Timothy M. Shanahan  Jonathan T. Overpeck  W. E. Sharp  Christopher A. Scholz  Justice A. Arko 《水文研究》2007,21(13):1678-1691

Historical changes in the level of Lake Bosumtwi, Ghana, have been simulated using a catchment‐scale hydrological model in order to assess the importance of changes in climate and land use on lake water balance on a monthly basis for the period 1939–2004. Several commonly used models for computing evaporation in data‐sparse regions are compared, including the Penman, the energy budget, and the Priestley–Taylor methods. Based on a comparison with recorded lake level variations, the model with the energy‐budget evaporation model subcomponent is most effective at reproducing observed lake level variations using regional climate records. A sensitivity analysis using this model indicates that Lake Bosumtwi is highly sensitive to changes in precipitation, cloudiness and temperature. However, the model is also sensitive to changes in runoff related to vegetation, and this factor needs to be considered in simulating lake level variations. Both interannual and longer‐term changes in lake level over the last 65 years appear to have been caused primarily by changes in precipitation, though the model also suggests that the drop in lake level over the last few decades has been moderated by changes in cloudiness and temperature over that time. Based on its effectiveness at simulating the magnitude and rate of lake level response to changing climate over the historical record, this model offers a potential future opportunity to examine the palaeoclimatic factors causing past lake level fluctuations preserved in the geological record at Lake Bosumtwi. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

A density‐dependent elastoplastic hydro‐mechanical model for unsaturated compacted soils     

D. A. Sun  D. C. Sheng  H. B. Cui  S. W. Sloan 《国际地质力学数值与分析法杂志》2007,31(11):1257-1279

This paper presents a three‐dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled‐suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water‐retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water‐retention behaviour is studied using data obtained from controlled‐suction wetting–drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress–strain‐strength behaviour and the effect of void ratio on the water‐retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka–Nakai criterion. Model predictions of the stress–strain and water‐retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

新疆天山北坡一次区域性暴雪形成机制及水汽输送特征分析     

万瑜 《沙漠与绿洲气象(新疆气象)》2024,18(4):9-16

利用高空、地面常规观测资料、NCEP/NCAR再分析资料，诊断分析了2017年2月新疆天山北坡一次区域性暴雪过程的特征及成因，结合GDAS再分析资料并采用HYSPLIT模式，模拟追踪水汽源地、主要水汽输送通道及其对水汽输送的贡献。结果表明：此次天山北坡暴雪是在典型后倾结构的高低空系统配置下产生的，中、高纬地区短波槽在东移过程中同位相叠加，为暴雪长时间维持提供了稳定的天气尺度背景；暴雪发生时位势不稳定性加强，中低层持续冷垫抬升是主要的动力机制，较强垂直风切变是降雪强度较大的重要原因，高低空急流耦合激发中尺度垂直上升支和次级环流圈，地形作用对暴雪有增幅作用；暴雪主要水汽源地位于阿拉伯半岛西侧的红海和伊朗高原西南侧的波斯湾至阿拉伯海北部一带，水汽通道主要集中在500～850 hPa，水汽辐合区位于700～850 hPa，中高层有偏西气流、中层有西南气流、低层有西北急流将水汽接力输送至暴雪区；利用HYSPLIT模式模拟发现，暴雪期间，西、东、南边界水汽输入均起重要作用，主要水汽输送通道分别为偏西路径、偏西南路径、局地水汽路径，1500 m高度的追踪，三者贡献率大致相当，3000 m高度，局地水汽和偏西路径水汽贡献率更大。  相似文献   

Detecting Arctic snow and ice cover with FY-1D global data     

References： 《极地研究(英文版)》2007,18(1):54-62

Chinese meteorological satellite FY-1D can obtain global data from four spectral channels which include visible channel(0.58-0.68 μm) and infrared channels(0.84-0.89 μm,10.3-11.3 μm,11.5-12.5 μm).2366 snow and ice samples,2024 cloud samples,1602 land samples and 1648 water samples were selected randomly from Arctic imageries.Land and water can be detected by spectral features.Snow-ice and cloud can be classified by textural features.The classifier is Bayes classifier.By synthesizing five d ays classifying result of Arctic snow and ice cover area,complete Arctic snow and ice cover area can be obtained.The result agrees with NOAA/NESDIS IMS products up to 70%.  相似文献   

京津冀城镇体系与水系结构的时空关系研究   总被引：1，自引：1，他引：1  

张凤  陈彦光  刘鹏 《地理科学进展》2020,39(3):377-388

京津冀地区人水关系矛盾突出,分形可以有效描述城镇体系和水系时空演化特征,从而揭示两者演化关系,为城市问题的解决提供一些理论和经验依据。论文采用分形理论中的网格维数和多分维谱,首先分别刻画了两者的时空演化特征,其次探讨了城镇体系和水系结构之间的时空关系,最后探究了水系结构退化的影响因素。主要结论有：① 1990—2010年,京津冀地区建设用地的网格维数升高、自相似性增强、从集聚向分散转变,意味着建设用地朝着空间填充程度增强、有序、分散的方向发展,而水系反之,证明两者具有不同的时空演化方向;② 21世纪10年代,京津冀的人水关系十分紧张,南水北调虽然缓和了京津冀用水问题,改善了大尺度上的水系结构,但在小尺度上改善有限;③ 越靠近城市中心,建设用地分形形态发育越成熟,结构越有序,越靠近外围越混乱无序;④ 京津冀地区水系退化,由自然和人为两方面因素造成,21世纪以后人为因素的影响较为显著。针对京津冀地区水系退化,提出如下政策建议：在城市建设过程中,一方面科学规划城市水系,重视低等级水系的保护;另一方面节约集约利用水资源,完善水资源管理机制。未来,需要进一步探索城市发展和水系的非线性关系,为城市可持续发展提供依据。  相似文献   

毛乌素沙地植被水分利用效率的时空格局     

王姣月  秦树高  张宇清 《中国沙漠》2020,40(5):120-129

水分利用效率（WUE）是衡量生态系统碳水循环耦合程度的重要指标，明晰其动态变化规律有助于判断区域植被生态建设是否与当地的自然条件相适应。利用基于CASA（Carnegie-Ames-Stanford Approach）模型得到的植被净初级生产力（NPP）数据和MODIS系列产品中的蒸散发（ET）数据，估算了2001—2016年毛乌素沙地植被的WUE，并探讨了其时空演变特征及与气象因子的关系。结果显示：（1）WUE的多年平均值为0.62 gC·mm^-1·m^-2，空间上自东向西递减，在不同植被类型间表现为栽培植物>灌丛>草甸>草原>荒漠；（2）WUE以0.009 gC·mm^-1·m^-2·a^-1的速率上升，东部地区变化尤为显著，NPP的快速增长是WUE呈增加趋势的主要原因；（3）WUE与各气象因子的相关程度由大至小依次为太阳辐射、降水量、风速和气温，分布在西部地区的荒漠植被WUE受气象因子影响最小。经过一系列生态建设工程的治理，毛乌素沙地大部分地区自2001年以来NPP和WUE均呈增加趋势，即生态系统在变“绿”的同时还实现了水分的高效利用，有利于当地生态环境的健康发展；但在水热条件较差的中西部地区，新建设的植被生长缓慢且导致蒸散发产生强烈变化，使WUE呈减少趋势，暴露出植被建设规模与水资源承载能力不匹配的问题，需引起格外重视。  相似文献   

黄河中下游沿线城市水资源利用效率的时空演变及影响因素   总被引：2，自引：1，他引：2  

巩灿娟  徐成龙  张晓青 《地理科学》2020,40(11):1930-1939

采用超效率DEA模型、GIS空间分析方法、动态面板的系统GMM估计方法对2010—2017年黄河中下游沿线城市水资源利用效率时空格局及影响因素进行分析，结果表明：① 黄河中下游沿线城市水资源利用效率整体由2010年的0.70波动下降为2017年的0.67，且区域内70%以上的城市水资源利用效率变动趋势与其一致；② 黄河中下游沿线城市水资源利用效率呈“U”型区域两侧相对较高，中间区域相对较低的空间分布态势，且空间分布重心始终位于地理重心的北方；③ 环境规制、经济发展水平、产业结构优化、技术水平对水资源利用效率呈显著正向影响，农田水利设施建设、城镇化对水资源利用效率呈显著负向影响。研究结论可为黄河流域生态保护与高质量发展的推进提供决策支持。  相似文献   

人类世可持续发展背景下的远程耦合框架及其应用   总被引：1，自引：1，他引：1  

孙晶  刘建国  杨新军  赵福强  覃驭楚  姚莹莹  王放  伦飞  王洁晶  秦波  刘涛  张丛林  黄宝荣  程叶青  石金莲  张劲松  唐华俊  杨鹏  吴文斌 《地理学报》2020,75(11):2408-2416

在全球一体化进程不断加深的背景下,国家与地区之间的联系日益紧密,产生了一系列跨国家、跨地区、多尺度的社会—经济—环境影响,远程耦合（Telecoupling,社会、经济、环境的远距离相互作用）科学概念和综合框架的提出为解决上述问题提供了新方法和新途径。为更好促进远程耦合综合框架的正确使用和规范推广,本文系统解析了远程耦合综合框架,厘清各组成部分的定义和功能,梳理了框架的应用现状;通过对3个中国典型案例的阐释,展示了远程耦合综合框架的使用方法、结果分析及由此得出的科学意义和政策价值;最后描述了远程耦合综合框架使用中需要重点关注的问题,并对其应用前景进行了展望。远程耦合综合框架的推广应用有助于以跨国家、跨地区、多尺度的视角,重新审视多个人类与自然耦合系统的相互作用,揭示隐藏的远距离地理空间作用的科学价值,服务于有关政策的制定和实施,促进全球社会、经济、环境的可持续发展。  相似文献   

Estimating evapotranspiration from small watersheds using a water and energy balance approach     

Chang‐Soo Rim 《水文研究》2008,22(5):703-714

Meteorological and environmental data measured in semiarid watersheds during the summer monsoon and winter periods were used to study the interrelationships among flux, meteorological and soil water variables, and to evaluate the effects of these variables on the daily estimation of actual evapotranspiration (AET). The relationship between AET and potential evapotranspiration (PET) as a function of soil water content, as suggested by Thornthwaite–Mather and by Morton, was studied to determine its applicability to the study area. Furthermore, multiple linear regression (MLR) analysis was employed to evaluate the order of importance of the meteorological and soil water factors involved. The results of MLR analysis showed that the combined effects of available energy, soil water content and wind speed were responsible for more than 70% of the observed variations in AET during the summer monsoon period. The analyses also indicate that the combined effects of available energy, vapour pressure deficit and wind speed were responsible for more than 70% of the observed variations in AET during the winter period. However, the test results of two different approaches, using the relationships between AET and PET as a function of soil water content, indicated some inadequacy. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Coupled surface and ground water models for investigating hydrological processes     

Ray‐Shyan Wu  Dong‐Sin Shih  Ming‐Hsu Li  Chia‐Ching Niu 《水文研究》2008,22(8):1216-1229

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