Standardized precipitation evapotranspiration index showsdrought trends in China

Standardized precipitation evapotranspiration index (SPEI), calculated from the difference between potential evapotranspirationand precipitation, showed dry and wet deviations from normal conditions. This is generally used as an indicator for droughtevolution trends in drought assessments, water resources management and other fields of hydrology. Using monthly mean surface airtemperature and precipitation collected from 160 meteorological stations across China for 1951—2009, spatial distributions of seasonaldrought trends and frequencies of extreme drought events were analyzed via SPEI. The results showed drying trends across the wholeof China. The most significant drought was in the west, north and northeast of China. It was, however, wet in some regions of northernXinjiang and the border regions of Sichuan and Yunnan. Drying trends existed for all four seasons, and were more obvious in springand autumn. Summer was always dry in the last 15 years, although with a drying trend insignificant at the 0.05 level. Furthermore, thefrequency of extreme drought increased significantly. Significant trends in temperature increase along with moderate trends in precipitationdecline were noted for many stations in the northeast and north of China. The combined effects of precipitation and temperaturecaused significant droughts in the country. In the Sichuan Basin, precipitation significantly decreased with no significant change intemperature. Drought in Sichuan Basin was largely attributed to decreasing precipitation. In recent years, extreme drought events increasedwith decreasing frequencies of precipitation events in many areas of China. Widespread drought trends and significant increasesin extreme drought events probably hindered China’s economic development. SPEI-detected drought trends were mostly consistentwith observed droughts in China, indicating that SPEI was an ideal index for monitoring drying trends.