Drought is one of the most harmful natural hazards in Gansu Province in Northwest China. The changes of precipitation affect the severity of drought. In order to recognize the trend of precipitation and understand the effect of rainfall change on water resources management and drought severity, Mann-Kendall test was used. Standardized Precipitation Index (SPI) was calculated to reconstruct the drought at different time scales and analyze the frequency of drought occurrence in the recent 50 years. The results show that the SPI is applicable in Gansu Province. The number of severe droughts differs among regions: it is more obvious as a 3-month drought in the Yellow River Basin and the Yangtze River Basin than in the Inland River Basin, and other droughts at 6-, 9-, and 12-month time scales have the same effect in the three regions. Mann-Kendall test results show that there is an upward trend in the summer periods and a downward trend in the autumn-winter-spring intervals ranging from 10.5 mm/10 years to -37.4 mm/10 years, which affect the local water resources management, droughts mitigation, and agriculture decision making. This situation poses challenges for future study.

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