Investigation about the correlation and propagation among meteorological, agricultural and groundwater droughts over humid and arid/semi-arid basins in China

The propagation of meteorological drought in the hydrological cycle not only leads to the deficits of surface soil moisture, which results in agricultural drought, but also probably affects groundwater to trigger groundwater drought. Improving the understanding about the correlation and propagation among meteorological, agricultural and groundwater droughts is necessary to lessen the risks resulted from them. Moreover, the distinction of the correlation and propagation over the basins with different climate conditions is not yet sufficiently understood. As a case study of the humid and arid/semi-arid basins in China, the standardized precipitation index, the standardized soil moisture index and groundwater drought index based on GRACE (Gravity Recovery and Climate Experiment) are used to characterize meteorological, agricultural and groundwater drought respectively over the Yangtze River Basin with a humid climate condition and Yellow River Basin with an arid/semi-arid climate condition. The Spearman rank correlation coefficient is applied to investigate the correlation and propagation among the above three types of drought in the two basins. The results indicated that: (1) The meteorological, agricultural and groundwater droughts in the Yangtze River Basin and the meteorological and agricultural droughts in the Yellow River Basin are decreasing from April 2002 to March 2020, while the groundwater drought in the Yellow River Basin is aggravating in recent years. (2) There is a strong link between meteorological and agricultural droughts, and the propagation time from meteorological to agricultural drought in summer and autumn is shorter than that in winter and spring in the two basins. When comparing the propagation time in the two selected basins, it is longer in the Yangtze River Basin. (3) Groundwater extraction may be the main factor in the aggravation of groundwater drought in the two basins, which is different from the contributors to agricultural drought, which is mainly the propagation of meteorological drought.