Variations In Drought Over China Based On The Modified Self-Calibrating Palmer Drought Severity Index

Of all natural hazards, drought is the most prolonged and extensive one in China. Drought develops slowly and its impacts are profound and complex. In this study, the Self-Calibrating Palmer Drought Severity Index (PDSI) was improved and calculated based on replacing potential evapotranspiration scheme and by using monthly mean meteorological data of 551 selected stations in China during the period of 1951~2005.By analyzing variations of PDSI, temperature, precipation over different regions, and the anomaly of atmospheric circulation in drought periods, we conclused that:(1) There is inter-annual variation in droughts in drought regions, and the inter-decadal variation is even more remarkable. For China as a whole, there is no significant long-term upward or downward trend detected in the percentage areas of drought. However, significant increases of drought areas are found in North China, Northeast China and eastern part of Northwest China in all seasons, especially after 1980s. Most northern China(except western Northwest China) has experienced severe and prolonged drought periods since late 1990s, during which extreme drought situations were unprecedented in some of the areas.(2) Further investigation revealed that variation in precipitation is one of the most caused of annual changes in droughts. In the long-term effects, the increasing temperature in Northeast China, North China and eastern part of Northwest China, especially in Winter, Spring and Autumn. While in most part of Northwest China and the Qinghai- Tibet plateau the increasing precipitation caused the downward trend of drought areas.(3) During the summer drought years, the circulation anomaly distributions are remarkable from lower to upper levels. The anomaly high pressure appears 500 hPa over Mongolia, which makes North China in the Control of anomaly Northeast winds. The Southwest winds weakened in the eastern China in the lowern level. In middle latitude, the westerly strengthened and blocked the cold air southward movement from high latitude.