Abstract: The frequent and long-lasting droughts have caused many adverse effects on the social economy and ecological environment. Understanding the drought characteristics in the Wei river basin is of great significance to the adjustment of regional economic structure and the rational utilization of water resources. Based on the monthly meteorological data set of 25 stations in the Wei river basin from 1980 to 2018 and the Penman-Monteith equation, the standardized precipitation evapotranspiration index (SPEI) of multiple time scales were calculated, and the spatial-temporal characteristics of drought were analyzed, including its evolution, trend, affected area, frequency and duration. The results showed that: (1) there was an obvious periodic variation of dry-wet status in the Wei river basin during the past 39 years, but the drying trend was appeared as a whole. The drought period was mainly concentrated in 1995−2009, among which the drought occurring stations ratio in 2000−2009 was the largest, with an average value of 36%. The longest drought duration was occurred in 2000−2009, about 3.6 months, and the shortest drought duration was occurred in1980−1989, about 1.6 months. (2) There was a trend of wetness in autumn, while the droughts in spring and summer was increasingly intensified, which was the main driving force of the inter-annual drought in the Wei river basin. (3) The droughts in the Wei river basin were dominated by mild and moderate droughts, but there were relatively more stations with severe and extreme droughts around 2000, among which the droughts occurred in 1997 had a higher degree and a wider range of impacts. (4) The variation of drought frequency for different drought levels at different time scales was consistent, showing that the higher the drought level, the lower the frequency. In addition, extreme droughts occurred more frequently at the annual scale, and the northeastern region of the Wei river basin was a drought-prone area in space. Above all, the drought condition in the Wei river basin was more severe from 2000 to 2009, and the droughts in the northern region was severer than that in the southern region, so more attentions should be paid to strengthening disaster prevention management in the northern area.

Key words: SPEI_PM, Multiple time scales, Meteorological drought, Spatial-temporal characteristics, Wei river basin