Changes of summer meteorological drought and their relationship with the dry and wet circulation patterns in the Huai River basin, China

Study region: Huai River basin, China. Study focus: There has been much research on the changes of droughts in the Huai River basin (HRB), China, however, the recent changes of meteorological drought and the relationship with circulation patterns are not understood well so far. This paper first explores the changes of summer meteorological drought in HRB, then obtains the characteristics of dry and wet circulation patterns (CPs) based on the self-organizing map neural network (SOM), and further analyzes the contribution of thermodynamic and dynamic effects to investigate the influences of circulation patterns on the changes of droughts. New hydrological insights: There was an insignificant weakening of summer meteorological drought in the HRB. Twelve circulation patterns are obtained based on SOM, and further classified into three types of dry, wet and intermediate patterns. The frequency of dry (wet) CPs showed a significant downward (upward) trend and dry (wet) CPs had shorter (longer) duration recently. Compared to dynamic effects (i.e., the changes of dry and wet CPs), the changes of summer drought were mainly driven by thermodynamic effects, which might be the reason why the weakening of summer drought was not significant in the HRB.