长江流域实际蒸散发演变趋势及影响因素

Analysis of actual evapotranspiration evolution and influencing factors in the Yangtze River Basin

长江流域是我国重要的水资源供给区域,流域生态系统的水资源供给不仅服务于流域内部,同时也通过南水北调服务于北方部分地区。实际蒸散发作为地表水文循环重要环节会直接影响到生态系统的水资源供给服务能力。在全球气候变暖与地表环境变化的背景下,分析长江流域实际蒸散发的演变趋势与成因,对于我国水资源供给和生态安全的保障有着重要的意义。在对比GLEAM_v3.2a、MOD16、GLDAS_Noah2、ERA_Interim四种常用蒸散发数据集精度的基础上,选择精度最优的GLEAM_v3.2a数据集,通过分段线性拟合、逐步回归和相关性分析了1981—2017年间长江流域地表实际蒸散发演变趋势和影响因素。结果表明:(1)长江流域实际蒸散发的演变具有明显的阶段性,1981—1997年为不显著下降阶段,下降速率为-0.02 mm/a,下降区域主要分布在长江流域西北和东部部分子流域,1998—2017年为全流域显著上升阶段,上升速率为1.94 mm/a;(2)日照时数下降速率减缓、植被指数增加速率升高是长江流域实际蒸散发阶段性变化的主要原因,气温突增、风速回升在长江流域实际蒸散发的长期增加趋势中也起到了重要的正向作用;(3)1998—2017年间,长江流域生态系统水资源供给服务量在实际蒸散发显著增加的影响下有所下降,流域西部地区下降趋势明显,旱情加剧;(4)建议在长江流域西部干旱地区优先加强对本地原生林的保护,同时在生态修复工程中选择针叶乔木等蒸腾能力弱的树种,以缓解旱情加剧的趋势。

The Yangtze River Basin is an important water resource supply area in China.The water resource supply service of the river basin ecosystem not only serves the interior of the river basin,but also serves parts of the north through the South-to-North Water Transfer Project.As an important part of the surface hydrological cycle,actual evapotranspiration will directly affect the ability of the ecosystem to provide water resources.Under the background of climate and surface environment changes,analysis of the evolutionary trend and causes of actual evapotranspiration in the Yangtze River Basin has important referential significance for the protection of water resources and ecological security in China.Based on the comparison of the accuracy GLEAM_v3.2a,MOD16,GLDAS_Noah2,and ERA_Interim four evapotranspiration data sets,we select the GLEAM_v3.2a data set with the best accuracy to analyze the evolution trend and influencing factors of the actual evapotranspiration in the Yangtze River Basin from 1981 to 2017.The results show that:(1)the evolution of the actual evapotranspiration in the Yangtze River Basin is staged.1981—1997 was an insignificant decline stage with a decline rate of-0.02 mm/a.The decline area was mainly distributed in the northwest and eastern parts of the Yangtze River Basin.1998—2017 was a significant rising stage of the whole basin,with an increasing rate of 1.94 mm/a.(2)The decreasing rate of sunshine hours and the increasing rate of vegetation index are the main reasons of periodic changes of the actual evapotranspiration in the Yangtze River Basin.The sudden increases of temperature and wind speed have also played the positive role in the long-term increase trend of actual evapotranspiration in the Yangtze River Basin.(3)Between 1998 and 2017,the water yield of ecosystem in Yangtze River Basin decreased due to the significant increase in actual evapotranspiration.The decline in the western region of the river basin was obvious,and the drought situation was intensified.(4)It is recommended to preferentially strengthen the protection of native forests in the arid areas in the western part of the Yangtze River Basin,and to select tree species with weak transpiration ability such as coniferous trees in afforestation projects,to alleviate the trend of increasing drought.