基于改进后地表湿润指数的我国西南干旱气候特征研究

Drought climate characteristics in Southwest China based on the modified surface humidity index

利用1961-2014年西南地区96个观测站日平均气温和降水资料、1961-2010年ERA-20C0.5°×0.5°再分析资料,运用REOF方法、计算地表湿润指数以及改进后的地表湿润指数,研究了西南地区干旱时空分布特征。结果表明:(1)综合REOF(旋转经验正交函数)前四个模态,除川西高原外,西南地区1961-2010年整体土壤湿度有所降低,其中以四川盆地和云贵高原南部下降趋势更为明显。(2)根据REOF空间模态对西南地区做出气候区划,以历年月平均降水和干旱气候区划为基础,对地表湿润指数做出改进。其结果显示,原地表湿润指数(SHI)与改进后地表湿润指数(MSHI)空间分布特征均与年降水量的空间分布特征存在一定的相似性,指数低值区与弱降水区吻合,西北部较为干燥,云贵高原南部较为湿润。(3)从空间分布上来看,MSHI在西南南部更接近降水的空间分布且空间连续性更好。从时间序列上来看,MSHI比SHI更能体现西南地区干旱年,用MSHI识别典型干旱年份,识别能力较强。研究结果对合理配置和利用水资源,进行未来气候变化研究有重要意义。

Based on the data of daily mean temperature and precipitation from 96 meteorology stations in South- west China and the ERA-20C reanalysis daily data from 1961 to 2014, using the method of REOF, the surface humidity index （SHI） and modified surface humidity index （MSHI） were calculated in order to study the time and space distribution characteristics in Southwest China. The following conclusions can be drawn ： （ 1 ） looking from the first four models of REOF, the soil moisture has decreased in the 50 years in Southwest China, except for the western Sichuan Plateau, especially obviously in the Sichuan Basin and southern Yunnan-Guizhou Plateau. （2） according to the result of REOF space modals, climatic division in Southwest China was able to present; based on different climatic divisions and monthly average precipitation, the surface humidity index （SHI） could be improved to modified surface moisture index （ MSHI）, as a result, both SHI and MSHI had certain similarities in annual precipitation on space distribution： low index area in accordance with the weak precipitation area, northwest being relatively dry, Yunnan-Guizhou Plateau being relatively moist in the south. （3） looking from the spatial distribution, MSHI was closer to the rainfall distribution than SHI; moreover, its spatial continuity was better; looking from the time series, compared with SHI, MSHI can reflect drought years better in South- west China. This study has important significance for water resource utilization and understanding climate change in the future.