Abstract: Based on the humidity index, using the daily climate data of 113 meteorological stations in and adjacent the Yellow River Basin(YRB) from 1960 to 2020, climate trend rate, Morlet wavelet, simple correlation analysis, and Hurst index were used to analysis the spatiotemporal characteristics of dry-wet condition in the YRB in the latest 61 years and to predict the future trend of dry-wet changes in the YRB, to provide scientific basis for drought prevention and mitigation and rational utilization of climate resources in the YRB. The results showed that: (1) among all the geographic zones, the annual and seasonal humidity index in the YRB was high in the southeastern YRB and low in the northwestern YRB. Spatially, the climate of the annual, spring and autumn in the YRB was mainly dry, the proportions of stations with significant decrease of humidity index of the total stations were 5.31%, 7.96% and 6.19%, respectively. The climate of summer and winter was mainly wet, the proportions of stations with significant increase of humidity index were 10.62% and 13.27%, respectively. (2) As for the interannual change, the annual and seasonal humidity index of the YRB from 1960 to 2020 showed no significant change. Semi-humid, semi-drought, semi-humid, semi-humid, semi-drought were found in entire year, spring, summer, autumn, and winter, respectively. The annual and seasonal humidity index of the YRB had periodic oscillation characteristics at multiple time scales, and the first main period was 3 years, 26 years, 14 years, 3 years and 15 years, respectively. (3) The change of humidity index in the YRB was extremely significantly positively correlated with precipitation and relative humidity. There was a extremely significant negative correlation between sunshine duration and humidity index. Precipitation, relative humidity, and sunshine duration were the main factors affecting the change of humidity index in the YRB. (4) The Hurst index of annual and seasonal humidity index in the YRB were larger than 0.50, indicating that the climate of annual, spring, and autumn of the YRB would continue to be drying, the summer and winter climate would continue to be wetting.

Key words: Humidity index, Future trend, Spatiotemporal variation, Morlet wavelet analysis, Yellow River Basin