| The Yangtze River Basin is China's largest watershed.The impact of the construction and storage of the Three Gorges Water Conservancy Project on the water cycle in the basin has become a hot issue for research.Water resources are one of the important resources for local economic development and ecological stability in the Yangtze River Basin.Evapotranspiration,as a key water energy flux between the ground and the atmosphere,is one of the most important ways to change water migration during the water cycle of the basin.Since the completion of the Three Gorges Water Conservancy Project in 2003,the water surface area in the basin has increased,and the impact of climate change has changed the water cycle process in the basin,which will cause changes in the temporal and spatial characteristics of evapotranspiration in the basin.Therefore,accurately calculating evapotranspiration in the Three Gorges Reservoir area and exploring its response mechanism to the impact of climate change and human activities are of theoretical significance for the study of energy and water exchange between land water cycles and land surface models,and for large reservoir engineering reservoir areas Water resources protection and sustainable use have practical application values.Based on the above reasons,this study chose the land surface model CLM4.5 as the simulation platform,and adopted an improved land surface-hydrological model that coupled the CLM with the human water extraction module,and combined with China Meteorological Forcing Dataset(CMFD)meteorological data as atmospheric forcing data.Using the MK nonparametric trend test,wavelet periodic analysis and other methods to analyze the climate and driving factor change trends,and using the MK mutation test to determine the mutation points of the change factors of each climate factor,for the actual evapotranspiration of key links in the water cycle,The water and energy fluxes of the Three Gorges Reservoir area were simulated to analyze the spatial and temporal distribution characteristics of the Three Gorges Water Conservancy Project.The main results obtained are as follows:(1)Reveals the regularity of water and energy flux in typical locations of the reservoir area.According to the characteristics of climate change such as the temperature and wind speed of typical observation stations,the temperature trend is basically consistent with the long-term trend.The wind direction is ESE wind-dominated,and the wind speed is mainly 0-4.The evolution process of water energy flux at different time scales.Among them,the latent heat flux on the daily scale showed a ‘single peak' trend;on the monthly scale,it showed a trend of high in summer and low in winter.(2)A land-hydrological model based on the social water cycle is constructed.Based on the analysis of moisture energy fluxes in typical locations,the atmospheric forcing data evaluated by multi-dimensional accuracy,the land use data completed by MODIS interpretation and USGS land cover data are used as surface parameter data,and the distributed human water withdrawal data are used as The input of the land surface-hydrological model system establishes a model of the water cycle process between the land-air system,and then optimizes the model parameters by observing data from typical sites to quantitatively reflect the impact of climate change and human activities on the water energy flux process.(3)The climate change characteristics of the Three Gorges Reservoir watershed and its response to water energy flux are revealed.On the time scale,the average temperature for many years is increasing.Among them,the annual average temperature,the average temperature of spring,autumn,and winter showed a significant upward trend,and the average temperature of summer showed an upward trend;the annual average precipitation,the precipitation of spring and autumn all showed a downward trend,and the precipitation of summer showed an upward trend.None were significant.On the spatial scale,the temperature in the tail region of the reservoir is relatively high,and the temperature in the central and southern parts of the reservoir and the northwest of the reservoir head is relatively low.The average temperature difference in the basin is about 6.2 ° C.Declining trend;the multi-year precipitation in the basin is mostly concentrated in the central reservoir area,and the annual average precipitation presents a decreasing distribution pattern from the middle to the east and west sides.(4)Analyze the variation law of water and energy flux at the spatiotemporal scale.The average annual evapotranspiration in the Three Gorges Reservoir area before the establishment of the reservoir was approximately 579.5 mm / a,the average evaporation in spring was 147.0 mm / a,the average evaporation in summer was 273.3 mm / a,and the average evaporation in autumn was 121.7 mm / a.The evaporation is 37.5 mm / a;the average annual evapotranspiration after the construction of the reservoir is 602.0 mm / a,the average evaporation in spring is 159.1 mm / a,the average evaporation in summer is 281.9 mm / a,and the average evaporation in autumn is 121.3 mm / a,the average winter evapotranspiration is 39.7 mm / a;spatially,the actual evapotranspiration and its subsurface evapotranspiration and vegetation transpiration are relatively consistent,showing an increasing trend in the central and eastern parts of the reservoir and southeast of the tail of the reservoir;Vegetation evaporation showed a decreasing trend in the reservoir after water storage compared with before water storage.In terms of change range,the amount of evapotranspiration decreased significantly in the middle of the reservoir,and the amount of evapotranspiration increased significantly in the end of the reservoir.This study started by simulating the latent heat flux in the basin of the Three Gorges Reservoir area,and improved the simulation accuracy by selecting a land surface-hydrological model that takes into account human water intake modules.Through the study of evapotranspiration simulation in the Three Gorges Reservoir area and the study of the temporal and spatial characteristics of evapotranspiration,it can provide scientific support for exploring the role of actual evapotranspiration in the regional water cycle after the completion of the Three Gorges Reservoir area and maintaining the sustainable development and protection of water resources in the Yangtze River Basin. |
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