Thermodynamic transport mechanism of water freezing-thawing in the vadose zone in the alpine meadow of the Tibet Plateau          下载免费PDF全文

Qiao Gang  Yu Feng-dan  Wang Wen-ke  Zhang Jun  Chen Hua-qing 《地下水科学与工程》2022,10(3):302-310

High altitude, cold and dry climate, strong solar radiation, and high evapotranspiration intensity have created an extremely fragile ecological and geological environment on the Tibet Plateau. Since the heat in the vadose zone is primarily generated by the external solar radiation energy, and evapotranspiration is contingent on the consumption of vadose heat, the intensity of evapotranspiration is associated with the intensity of solar radiation and the heat budget in the vadose zone. However, the spatial and temporal variation of heat budget and thermodynamic transfer process of the vadose zone in the frigid region are not clear, which hinders the revelation of the dynamic mechanism of evapotranspiration in the vadose zone in the frigid region. With the moisture content of the vadose zone in the alpine regions being the research object, the paper conducts in-situ geothermal observation tests, takes meteorological characteristics into consideration, and adopts the method of geothermal gradient and numerical computation to analyse the temporal and spatial variation rule of heat budget and thermodynamic transmission process of the vadose zone in the high and cold regions. The results show there is a positive correlation between air temperature, ground temperature, and water content of the vadose zone in both thawing and freezing periods. According to the change law of geothermal gradient, the thermodynamic transfer process of the vadose zone has four stages: slow exothermic heating, fast endothermic melting, slow endothermic cooling, and fast exothermic freezing. From the surface down, the moisture freezing rate of the vadose zone is slightly higher than the melting rate. This is of great significance for understanding the evapotranspiration dynamic process of the vadose zone and protecting and rebuilding the ecological and geological environment in the high and cold regions.  相似文献   

Evaluating a satellite-based seasonal evapotranspiration product and identifying its relationship with other satellite-derived products and crop yield: A case study for Ethiopia     

《International Journal of Applied Earth Observation and Geoinformation》2015

Satellite-derived evapotranspiration anomalies and normalized difference vegetation index (NDVI) products from Moderate Resolution Imaging Spectroradiometer (MODIS) data are currently used for African agricultural drought monitoring and food security status assessment. In this study, a process to evaluate satellite-derived evapotranspiration (ETa) products with a geospatial statistical exploratory technique that uses NDVI, satellite-derived rainfall estimate (RFE), and crop yield data has been developed. The main goal of this study was to evaluate the ETa using the NDVI and RFE, and identify a relationship between the ETa and Ethiopia’s cereal crop (i.e., teff, sorghum, corn/maize, barley, and wheat) yields during the main rainy season. Since crop production is one of the main factors affecting food security, the evaluation of remote sensing-based seasonal ETa was done to identify the appropriateness of this tool as a proxy for monitoring vegetation condition in drought vulnerable and food insecure areas to support decision makers. The results of this study showed that the comparison between seasonal ETa and RFE produced strong correlation (R² > 0.99) for all 41 crop growing zones in Ethiopia. The results of the spatial regression analyses of seasonal ETa and NDVI using Ordinary Least Squares and Geographically Weighted Regression showed relatively weak yearly spatial relationships (R² < 0.7) for all cropping zones. However, for each individual crop zones, the correlation between NDVI and ETa ranged between 0.3 and 0.84 for about 44% of the cropping zones. Similarly, for each individual crop zones, the correlation (R²) between the seasonal ETa anomaly and de-trended cereal crop yield was between 0.4 and 0.82 for 76% (31 out of 41) of the crop growing zones. The preliminary results indicated that the ETa products have a good predictive potential for these 31 identified zones in Ethiopia. Decision makers may potentially use ETa products for monitoring cereal crop yields and early warning of food insecurity during drought years for these identified zones.  相似文献   

遥感技术应用于地表面蒸散发的研究进展   总被引：31，自引：4，他引：27  

郭晓寅  程国栋 《地球科学进展》2004,19(1):107-114

蒸散既是地表水分循环的重要组成部分,也是能量平衡的主要项。地表热量、水分收支状况在很大程度上决定着地理环境的组成和演变,清楚地认识蒸散发,对了解大范围内能量平衡和水分循环具有重要意义。目前,已发展了从 传统方法、模拟方法到遥感方法的很多种方法用于估算蒸散发。遥感方法以其能够获知大范围地表特征信息的优势为较准确估算地表蒸散发提供了可能,从而受到人们的日益重视。介绍了研究蒸散发的各种方法,并探讨了利用遥感方法研究蒸散发的优缺点和未来的发展前景。  相似文献   

阿克苏河灌区作物需水量对气候变化的敏感性分析     

王志成 《沙漠与绿洲气象(新疆气象)》2018,12(3):33-39

阿克苏河灌区是中纬度干旱区典型的绿洲灌溉系统,同时也是新疆第二大灌区,了解灌区作物需水量可为灌区种植结构调整、水资源优化配置提供科学依据。本研究基于联合国粮农组织(FAO)的Penman-Monteith蒸散发模型,结合作物系数法估算了阿克苏灌区作物需水量的时空变化及其对气候因子和作物种植结构的敏感性。结果表明,1960—2015年阿克苏灌区多年平均作物需水量为586 mm,且呈显著上升趋势,上升速率为38.43 mm/10 a。随着气候变化和作物种植结构的改变,1990—2015年间作物需水量急剧增加,增加速率高达99.37 mm/10 a。对于不同作物类型,果林的需水量最大,高达829.8 mm,其次是棉花、水稻和玉米,小麦需水量最低。阿克苏灌区的作物需水量对日最高气温和日照时数较为敏感,而对最低气温、风速和水汽压的敏感度较低。当日最高气温升高2℃时,作物需水量增加4%,当日照时数增加10%时,作物需水量将增加3.2%。另外,作物需水量对作物种植结构非常敏感,当果林的种植面积比例增加10%时,作物需水量增加了12.1%。  相似文献   

Evaluating five remote sensing based single-source surface energy balance models for estimating daily evapotranspiration in a humid subtropical climate     

《International Journal of Applied Earth Observation and Geoinformation》2016

In the last two decades, a number of single-source surface energy balance (SEB) models have been proposed for mapping evapotranspiration (ET); however, there is no clear guidance on which models are preferable under different conditions. In this paper, we tested five models-Surface Energy Balance Algorithm for Land (SEBAL), Mapping ET at high Resolution with Internalized Calibration (METRIC), Simplified Surface Energy Balance Index (S-SEBI), Surface Energy Balance System (SEBS), and operational Simplified Surface Energy Balance (SSEBop)—to identify the single-source SEB models most appropriate for use in the humid southeastern United States. ET predictions from these models were compared with measured ET at four sites (marsh, grass, and citrus surfaces) for 149 cloud-free Landsat image acquisition days between 2000 and 2010. The overall model evaluation statistics showed that SEBS generally outperformed the other models in terms of estimating daily ET from different land covers (e.g., the root mean squared error (RMSE) was 0.74 mm day⁻¹). SSEBop was consistently the worst performing model and overestimated ET at all sites (RMSE = 1.67 mm day⁻¹), while the other models typically fell in between SSEBop and SEBS. However, for short grass conditions, SEBAL, METRIC, and S-SEBI appear to work much better than SEBS. Overall, our study suggests that SEBS may be the best SEB model in humid regions, although it may require modifications to work better over short vegetation.  相似文献   

Operational evapotranspiration estimates from SEVIRI in support of sustainable water management     

《International Journal of Applied Earth Observation and Geoinformation》2016

This study aimed at evaluating the accuracy of the evapotranspiration (ET) operational estimates from the Meteosat Second Generation (MSG) Spinning Enhanced Visible Infra-Red Imager (SEVIRI) at a range of selected ecosystems in Europe. For this purpose in-situ eddy covariance measurements were used, acquired from 7 selected experimental sites belonging to the CarboEurope ground observational network over 2 full years of observations (2010–2011). Appraisal of ET accuracy was also investigated with respect to land cover, season and each site(s) degree of heterogeneity, the latter being expressed by the fractional vegetation cover (FVC) operational product of SEVIRI.Results indicated a close agreement between the operational product’s ET estimates and the tower based in-situ ET measurements for all days of comparison, showing a satisfactory correlation (r of 0.709) with accuracies often comparable to previous analogous studies. For all land cover types, the grassland and cropland sites exhibited the closest agreement (r from 0.705 to 0.759). In terms of seasons the strongest correlations were observed during the summer and autumn (r of 0.714 & 0.685 respectively), and with FVC the highest correlation of 0.735 was observed for the class FVC 0.75-1 when compared against the observed values for the complete monitoring period. Our findings support the potential value of the SEVIRI ET product for regional to mesoscale studies and corroborate its credibility for usage in many practical applications. The latter is of particular importance for water limiting environments, such as those found in the Mediterranean basin, as accurate information on ET rates can provide tremendous support in sustainable water resource management as well as policy and decision making in those areas.  相似文献   

A comparison of ASCE and FAO-56 reference evapotranspiration for a 15-min time step in humid climate conditions     

Ayman A. Suleiman  Gerrit Hoogenboom   《Journal of Hydrology》2009,375(3-4):326-333

Many applications in diverse disciplines require estimates of evapotranspiration (ET) at hourly or smaller time steps. The primary objectives of this study were to compare the American Society of Civil Engineers (ASCE) and FAO-56 Penman–Monteith equations for 15-min ET₀ (ET_{0,15-min,ASCE} and ET_0,15-min,FAO) estimations for humid climate conditions and to compare the 24 h sum of ASCE (ET_0,24 h,ASCE) and FAO-56 15-min ET₀ (ET_0,24 h,FAO) with the daily ET₀ (ET_0,d,FAO) computed from the daily FAO-56 equation, which is identical to ASCE daily ET₀ equation. Ten-year, i.e., 1997–2006 continuous 15-min and daily weather data for 11 representative and well-distributed sites throughout Georgia, USA were used. It was evident that during the day, ET_{0,15-min,ASCE} was higher than ET_0,15-min,FAO due to a lower surface resistance parameter value, while at night ET_{0,15-min,ASCE} was lower than ET_0,15-min,FAO due to a higher surface resistance parameter value. The ET_0,15-min,FAO was about 5% less than ET_{0,15-min,ASCE} and ET_0,24 h,FAO was about 5% lower than ET_0,24 h,ASCE. The difference between ET_{0,15-min,ASCE} and ET_0,15-min,FAO during the day and night was highly dependent on wind speed. During the three summer months, i.e., June, July and August, on average, ET_0,24 h,FAO was only 1% higher than ET_0,d,FAO while ET_0,24 h,ASCE was 5% higher than ET_0,d,FAO. For the entire year, ET_0,24 h,FAO was 8% higher than ET_0,d,FAO while ET_0,24 h,ASCE was 13% higher than ET_0,d,FAO. The ET_0,24 h,FAO and ET_0,d,FAO had a better agreement than ET_0,24 h,ASCE and ET_0,d,FAO throughout the year and during the summer months. It is also worth noting that the daily calculations for FAO-56 and ASCE were identical. These results demonstrated that for applications that require 15-min time steps or daily ET₀ for the entire year, the use of ET_0,15-min,FAO and ET_0,24 h,FAO, respectively, will yield more consistent outcomes. The use of ET_0,d,FAO during the summer months can be as accurate as the use of ET_0,24 h,FAO for applications that require daily time steps, such as irrigation scheduling.  相似文献   

Water balance modeling over variable time scales based on the Budyko framework – Model development and testing     

Lu Zhang  Nick Potter  Klaus Hickel  Yongqiang Zhang  Quanxi Shao 《Journal of Hydrology》2008,360(1-4):117-131

Partitioning of precipitation into evapotranspiration and runoff is controlled by climate and catchment characteristics. The degree of control exerted by these factors varies with the spatial and temporal scales of processes modeled. The Budyko framework or the “limits” concept was used to model water balance at four temporal scales (mean annual, annual, monthly and daily). The method represents a top-down approach to hydrologic modeling and is expected to achieve parsimony of model parameters. Daily precipitation, potential evapotranspiration, and streamflow from 265 catchments in Australia were used. On a mean annual basis, the index of dryness defined as the ratio of potential evapotranspiration to precipitation was confirmed to be a dominant factor in determining the water balance with one model parameter. Analysis of the data, however, suggested increased model complexity is necessary on finer time scale such as monthly. In response, the Budyko framework for mean annual water balance was extended to include additional factors and this resulted in a parsimonious lumped conceptual model on shorter-time scale. The model was calibrated and tested against measured streamflow at variable time scales and showed promising results. The strengths of the model are consistent water balance relationships across different time scales, and model parsimony and robustness. As result, the model has the potential to be used to predict streamflow for ungauged catchments.  相似文献   

基于遥感的鄱阳湖湖区蒸散特征及环境要素影响   总被引：1，自引：0，他引：1  

赵晓松  刘元波  吴桂平 《湖泊科学》2013,25(3):428-436

蒸散是湖泊湿地生态系统水循环的重要组成部分,研究湖区地表蒸散量的时空变化对了解鄱阳湖湖区水量平衡关系具有重要意义.本研究基于MODIS数据,应用地面温度-植被指数三角关系法反演2000-2009年鄱阳湖湖区的实际蒸散量,分析湖区蒸散的时空分布特征及主要气象因子对流域蒸散的影响.结果表明:2000-2009年鄱阳湖湖区年蒸散量在685~921 mm之间,平均年蒸散量为797 mm,最大蒸散量出现在2004年.2000-2009年多年平均水体蒸发量为1107 mm,高于湖区植被蒸散量(774 mm).湖区汇水区域中蒸散量占降水的平均比例为55%,是水量平衡的主要支出项,径流系数约为0.45.湖区蒸散主要受辐射和气温的影响,月蒸散量与气温呈显著的指数相关,2007年蒸散量对温度的关系最为敏感.降水量距平与蒸散量距平的关系除2007年呈显著负相关外,其他年份相关性不显著.鄱阳湖湿地蒸散与湖泊水域面积总体呈正相关,但在水文干旱严重的2006年,当水域面积<30%时,蒸散速率随水域面积增加而减小.  相似文献   

基于双源蒸散和混合产流的分布式水文模型构建及应用--以辽河老哈河流域为例     

刘晓帆  任立良  徐静  袁飞 《湖泊科学》2011,23(2):174-182

以北方半干旱地区的辽河老哈河流域为研究对象,采用网格离散化方法进行水文模拟单元划分,利用具有物理基础的双源蒸散发能力估算模型,计算每个栅格单元的截留蒸发、植被蒸腾能力和土壤蒸发能力,并取代蒸发皿资料作为混合产流模型的蒸散发能力输入,从而构建摹于双源蒸散与混合产流的分布式水文模型,并对老哈河流域1970-1979年的日径...  相似文献