Spatiotemporal variability of four precipitation-based drought indices in Xinjiang, China

Global increases in duration and prevalence of droughts require detailed drought characterization at various spatial and temporal scales. In this study, drought severity in Xinjiang, China was investigated between 1961 and 2012. Using meteorological data from 55 weather stations, the UNEP (1993) index (I-A), Erinc's aridity index (I-m), and Sahin's aridity index (I-sh) were calculated at the monthly and annual timescales and compared to the Penman-Monteith based standard precipitation evapotranspiration index (SPEIPM). Drought spatiotemporal variability was analyzed for north (NX), south (SX), and entire Xinjiang (EX). I-m could not be calculated at 51 stations in winter as T-max was below 0. At the monthly timescale, I-A, I-m, and I-sh correlated poorly to SPEIPM because of seasonality and temporal variability, but annual I-A, I-m, and I-sh correlated well with SPEIPM. Annual I-A, I-m, and I-sh showed strong spatial variability. The 15 extreme droughts denoted by monthly SPEIPM occurred in NX but out of phase in SX. Annual precipitation, maximum temperature, and relative and specific humidity increased, while air pressure and potential evapotranspiration decreased over 1961-2012. The resulting increases in the four drought indices indicated that drought severity in Xinjiang decreased, because the local climate became warmer and wetter.Chinese National Science Foundations [U1203182, 51579213]; State Foundation for Studying Abroad [201506305014]; China 111 projectMinistry of Education, China - 111 Project [B12007]This study was financially supported by the Xinjiang Joint Project of the Chinese National Science Foundations (U1203182, 51579213), the State Foundation for Studying Abroad (201506305014), and China 111 project (B12007). We also thank the Meteorological Data Sharing Service Network in China (cdc.nmic.cn) for supplying weather data. The constructive comments of three anonymous reviewers strengthened the analyses of this paper