Drought severity and change in Xinjiang, China, over 1961–2013

Monthly climatic data from 53 sites across Xinjiang, China, were used to compare drought severity from the widely accepted Standardized Precipitation Index (SPI) with the recently proposed Standardized Precipitation Evapotranspiration Index (SPEI), as well as trends in the data from 1961 to 2013. Monthly Thornthwaite based (ET_o.TW) and Penman-Monteith based reference evapotranspiration (ET_o.PM) were computed and subsequently used to estimate SPEI_TW and SPEI_PM, respectively. The indices’ sensitivity, spatiotemporal distributions and trends were analyzed. The results showed that the TW equation underestimated ET_o, which affected the accuracy of the SPEI estimation. Greater consistency was found between SPI and SPEI_PM than between SPI and SPEI_TW at different timescales. SPI and SPEI_PM were sensitive to precipitation, but SPEI_TW and SPEI_PM were insensitive to ET_o. The scope of spatial SPEI_PM was wider than that of SPI at the same timescale. Obvious differences in SPI, SPEI_TW and SPEI_PM existed between northern and southern Xinjiang. SPEI_PM was a better indicator of global warming than SPI. Both SPI and SPEI_PM had increasing trends, which contradict previously reported trends in global drought. In conclusion, the decrease in drought severity observed over the last 53 years may indicate some relief in the water utilization crisis in Xinjiang, China.