Abstract: Using the measured precipitation and temperature data from the meteorological stations in and around the Qaidam Basin,the values of standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI) were calculated to describe the drought characteristics in the study area at different time scales. However,limited by the sparse distribution of stations,these two indexes were insufficient in evaluating the drought features in the region.Based on the globally distributed scPDSIpm data sets,in this study the Palmer drought severity index (PDSI) was used to analyze the characteristics of drought evolution and spatiotemporal distribution of drought in the whole study area.Results are as follows: ① It could be seen that the effect of temperature on drought was significant at inter-annual scale but not at monthly or seasonal scale; ② The correlation coefficients between PDSI index and the SPEI and SPI indices were higher than 0.7.In addition,PDSI was more suitable for evaluating drought in the areas without observed data; ③ As a whole,drought was the most serious in the central Qaidam Basin,and the occurring frequency of drought was low in the eastern marginal zone and the northwestern part of the study area.However,the situation had been greatly improved since 2000.This study has important guiding significance for evaluating the suitability of different drought indexes and drought evaluation in ungauged basins.

Key words: drought index, SPI, SPEI, PDSI, drought trend, spatiotemporal variation, the Qaidam Basin