The spatio-temporal variability of droughts using the standardized precipitation index in Yunnan, China

Based on the daily precipitation data from 33 meteorological stations in Yunnan Province from 1959 to 2013, the standardized precipitation index was calculated to analyze the drought frequency, station proportion, and drought intensity. The following conclusions were drawn from the analysis: (1) Drought exhibited a well-defined spatial-temporal variability characteristic. The drought frequency was much higher in the central and western areas of Yunnan, although it was the opposite throughout most of the southwestern and eastern regions. In past decades, centers with a high probability of drought was found: In the 1960s, it was located in the northwestern region of Yunnan. It was found in the northwestern and southeastern areas in the 1970s, the central region in the 1980s, the northwestern area in the 1990s, and central Yunnan and western Yunnan after 2000. (2) The drought frequency and intensity both increased at multiple timescales. The affected areas exhibited a well-defined upward trend in summer, autumn and winter. (3) The drought was normalized in Yunnan. However, in 1973, there was no severe inter-annual drought event. Moreover, there is 7% of the observed months in which no drought occurred. (4) The drought intensity increased at multiple timescales, especially in the summer and autumn. (5) There was a piecewise linear correlation between the drought area and the drought intensity. The enhancement of the intensity coincided with an increase in the affected areas. When the intensity value exceeded 1.5, the drought area decreased immediately, although it exhibited linear positive correlation with intensity.