Spatial and temporal evolution of drought and its relationship with climate factors in the Haihe River Basin

With the standardized precipitation evapotranspiration index (SPEI) used as the drought reflection index, the Mann-Kendall (M-K) trend test was used to analyze the drought change of the Haihe River Basin, the empirical orthogonal function analysis method was used to analyze main modes of drought distribution, and cross wavelet transform and Pearson correlation analysis were adopted to study the correlations between sunspots, large-scale circulation factors, and drought in the Haihe River Basin on monthly, seasonal, and annual scales, respectively. The results show that from 1960 to 2017, the Haihe River Basin developed to aridity, with SPEI decreasing 0.16 per decade on annual scale, 0.015 per decade on seasonal scale, and 0.004 per decade on monthly scale, respectively; the first mode of drought distribution of the Haihe River Basin was the global uniform distribution pattern, and the second mode was the south-north inverse distribution pattern, reflecting the influence of latitude on the drought distribution; among the atmospheric circulation factors, Niño3.4 has a high correlation with drought in the Haihe River Basin (with negative correlation on the annual and seasonal scales and positive correlation on monthly scale), and sunspots have a significantly negative correlation with drought in the Haihe River Basin and also have a profound impact on the occurrence of drought events in the Haihe River Basin.