关于我国北方干旱化及其转折性变化

过去半个世纪，中国经历了北方的"西湿东干"和东部的"南涝北旱"的降水分布格局。近十几年来，这种降水长期变化的分布格局是维持还是发生了变化?针对这个问题，本文基于年降水观测数据、自矫正的帕尔默干旱指数scPDSI、地表湿润指数SWI及GRACE（Gravity Recovery and Climate Experiment）卫星数据反演的陆地水储量（TWS）对中国区域干旱化问题进行了再分析。结果表明，近16年（2001~2016年），中国东部地区（100°E以东）"南涝北旱"的格局正在发生显著的变化，长江上中游及江淮流域已转为显著的干旱化趋势，而华北地区的降水已转为增加趋势，东部"南旱北涝"的格局基本形成；北方过去的"西湿东干"也转变为"西干东湿"的空间分布特征。显然，中国区域的降水格局在2001年后发生了明显的年代尺度转折性变化，两种常用干旱指数scPDSI和SWI的分析也证明了这一点。但GRACE的陆地水储量（TWS）的分析却显示，最近16年来，中国东部"南涝北旱"的格局仍未发生变化，北方大部分地区仍然处于干旱化的时段，且有加剧的趋势，其原因有待于进一步研究。

Drying Trend in Northern China and Its Shift during 1951-2016

There are significant changes in precipitation over China under global warming. During 1951-2000, the precipitation experienced a period when its spatial distribution showed a pattern of 'western wetting and eastern drying, WWED'in northern part of China and 'southern flooding and northern drought, SFND' in eastern part of China. Does this distribution pattern of long-term precipitation change still maintain or change after 2001? Based on observations of monthly mean temperature, monthly mean precipitation, and calculated self-calibrating Palmer Drought Severity Index (scPDSI) and surface wetness index (SWI), the drying trend in China has been revisited. Results show that the wet-dry spatial distribution in China has been changing significantly after 2001. Over northern China, the pattern of WWED switched to 'western drying and eastern wetting, WDEW'; over eastern China, the pattern of SFND changed to 'southern drought and northern flooding, SDNF' during 2001 to 2016. In central part of northern China, precipitation trend switched from a decreasing trend to a significant increasing trend; precipitation in the upper and middle reaches of Yangtze River experienced a shift from significant increasing trend to a decreasing trend. However, according to the analysis of Terrestrial Water Storage (TWS) data of The Gravity Recovery and Climate Experiment (GRACE), the wet-dry pattern of SFND over eastern China has not changed during 2001-2016, and the drying trend in northern China has been intensifying since 2001. This is opposite to the results shown in precipitation. The reason will be studied in the future.