Spatial and temporal evolution characteristics and causes of drought and flood in the Henan section of the Yellow River

Under the background of global warming, it is very important to explore the spatial–temporal evolution and causes of regional drought/flood for the realization of drought relief and social sustainable development. In this paper, the spatial–temporal characteristics of drought/flood in the Henan section of the Yellow River in recent 51 years were analyzed on the basis of the Standardized Precipitation Evapotranspiration Index (SPEI), and the methods such as wavelet analysis and empirical orthogonal decomposition. Combined with sunspot, atmospheric circulation factors and the operation of reservoir, the response of drought/flood to various factors were explored by using the sliding correlation analysis and cross wavelet analysis. The results showed that: (1) In terms of time scale, the SPEI-12 showed an insignificant trend of aridity on the whole and with main cycle of 18 years and sub cycles of 4 years and 8 years. (2) The first spatial distribution mode coefficients were all positive, indicating that the drought/flood changes in the entire region were consistent, while the second mode coefficients showed the east–west reverse differences, reflecting opposite drought/flood characteristics in the east and west. (3) In terms of causes, droughts and floods were affected by natural factors. The SPEI-12 had a period of 8–12 years with the sunspot phase logarithm and it had resonance periods of different time scales with the Arctic Oscillation (AO), El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), but it did not have a significant resonance period with the North Atlantic Oscillation (NAO). The flood storage and drought compensation function of the reservoir affected the occurrence of drought/flood events under natural conditions.