Refined spatiotemporal analysis of drought characteristics under different characteristic variable matchings: a case study of the middle reaches of the Yellow River basin, China

The refined assessment of the spatiotemporal characteristics of droughts is of great significance for drought evaluation. Based on monthly precipitation and temperature grid data (1961-2019) in the middle reaches of the Yellow River basin (MYRB), the standardized precipitation evapotranspiration index (SPEI) was calculated at monthly, seasonal, and annual scales. The run theory was used to extract the drought features at the monthly scale, and the spatiotemporal characteristics of different drought levels were analyzed using Mann-Kendall mutation tests and spatial interpolation. The Moran' I was used to analyze the spatial heterogeneity of droughts. The results showed that the drought trend in the MYRB increased from 1961 to 2019, with the SPEI exhibiting an overall decreasing rate of - 0.1145/decade. Decreasing rates were observed in spring (- 0.1356/decade), summer (- 0.0362/decade), and autumn (- 0.0745/decade), whereas an increasing rate was observed in winter (0.0781/decade). Only extreme droughts were long term, with an intensity as low as -22.29. The highest frequencies were observed for mild-moderate droughts, which mainly showed high-value clusters in the western and central regions. The frequencies of severe-extreme droughts mainly presented low-value clusters in the northern and southwestern areas. The frequencies of mild and severe droughts exhibited significant spatial cluster characteristics, while the drought intensity showed non-significant spatial clusters and a random distribution. The high and low values of drought intensity were mainly clustered in the middle-upper reaches. The research results provide reference for disaster prevention and mitigation, agricultural planning, and water resource allocation in the MYRB.