摘要
The Dali River Basin is located in northwest China and is a typical fragile ecosystem area. This region is extremely sensitive to climatic changes, and monitoring these changes can therefore provide an important basis for decreasing the losses bought about by drought disasters. On the basis of the standard precipitation index (SPI), the variation in drought characteristics and their relationship with extreme precipitation events in the Dali River Basin from 1971 to 2017 were analyzed. The main results of this study suggest that (1) the annual precipitation initially showed an increasing trend (from 1971 to the early 1990s) and fluctuated before the mid-1990s before it decreased and then increased. The precipitation in the months from January to March, August, and December showed a downward trend, whereas the precipitation in the other months showed an upward trend, which was particularly notable for the month of September. SPI1 and SPI3 were suitable for identifying short-term meteorological drought and flood characteristics, whereas SPI6 and SPI2 were suitable for revealing the long-term impact and duration of regional droughts and floods. Temporal variations in the SPI (particularly SPI3 and SPI12) increased significantly. (2) However, the trend of the SPI and the frequency of drought grade differed through the seasons. In winter, there was a definite downward trend, whereas in the other seasons the trend was an increasing one, particularly in autumn. The interannual SPI fluctuated greatly, showing an increasing trend overall, particularly since 2001. Light drought and moderate drought were the predominant drought grades (21.2%-36.1%), and the frequency of drought in summer and autumn was the highest. (3) The average duration, longest duration, and descending speed of drought events at a long time scale were higher than those at a short time scale. In addition, the frequency of days with daily precipitation ≥0.1 mm was not significantly changed over the study duration, which indicates that the possibility of drought had not increased significantly in the Dali River Basin over the 47-year-range studied. (4) The increase in the precipitation concentration (Rmax/Rtotal) will lead to a decrease in SPI1 and will increase the possibility of drought. By contrast, an extreme precipitation will reduce the probability of drought. With the increase in the maximum daily precipitation (>50 mm), the annual SPI increased and reduced the possibility of drought.
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