Evolution of meteorological and hydrological droughts in the upper reaches of the Yangtze River and the coupled response study

Drought is one of the most common natural hazards, and clarifying the response relationship between meteorological and hydrological droughts in changing environments facilitates drought forecasting and guidance in watersheds. This article analyses the spatial and temporal evolution of meteorological and hydrological droughts using the standardised precipitation index and the standardised runoff index on multiple scales. Drought characteristic variables are identified based on run theory, constructing ARIMA (autoregressive integrated moving average) prediction models for different timescales, and the corresponding relationships analysed with the help of the binary cross-wavelet and Copula functions. The results show that (1) meteorological and hydrological droughts have been aggravated since 1961. (2) The frequency of meteorological droughts in the upper Yangtze River basin varies relatively at the annual scale, with high spatial distribution in the northeast and low distribution in the west and southwest. (3) There is a positive correlation between meteorological and hydrological droughts, and there is a noticeable lag in the propagation of meteorological droughts to hydrological droughts. Analysing the spatial and temporal evolution of meteorological and hydrological droughts in the upper reaches of the Yangtze River and the response relationship can guide the timely formulation of future drought prevention and control measures.