Applicability Study of SPI in Multiple Time Scales in Meteorological Drought Monitoring in Anhui Province
Based on daily precipitation data, soil moisture data and historical drought disaster data of 81 meteorological stations in Anhui Province from 1961 to 2017, this paper studies the applicability of SPI in six time scales in meteorological drought monitoring in Anhui Province, by analyzing the interannual variation, seasonal evolution, spatial distribution, and frequency distribution of the drought days, evolution of typical drought processes as well as correlations of drought days to soil moisture and to drought disaster. The results show that in drought monitoring there is significant difference in the SPI in different time scales. In interannual variation of drought days and frequency distribution of the drought at different grades, the diagnosis results got with SPI of each time scale are in accordance with the fact, but the results are not in accordance with the fact of seasonal variation and spatial difference of drought days. SPI of each time scale has a good diagnostic effect on the interannual variation of drought days and frequency distribution of the drought at different grades, but it has a poor effect on the seasonal variation and spatial difference of drought days. From the perspective of diagnosis of typical drought processes, the shorter the time scale, the higher the weight of the precipitation, thus the SPI monitoring curve is too sensitive to precipitation, such as SPI30 and SPI60. However, the response of SPI150 and SPI180 of long-time scale to precipitation is too insensitive. From the perspective of correlation with soil moisture, the short-time scale SPI30 has close correlation with surface soil moisture of 10 cm depth and the correlation coefficient is 0.91, while the long-time scale SPI180 has close correlation with deep soil moisture of 50 cm depth. In the aspects of negative correlation between SPI in different time scales and annual precipitation and the positive correlation between them and drought disaster, correlation coefficients first increase and then decrease with the time scale prolonging, and the moderate-time scale SPI120 has the closest correlation to them. Overall, SPI in different time scales represent different meanings, and the drought in different time scales should be monitored and evaluated by SPI in different time scales.