Abstract: Based on the observation data of monthly temperature and precipitation in Mulei county, Xinjiang province during 1970—2020, trend analysis, M-K mutation test, wavelet power spectrum analysis and correlation analysis were used to study the variation characteristics and influencing factors of the relative humidity index in spring and summer in Mulei county. The results showed that the average temperature and evapotranspiration in spring and summer in Mulei county had a significant increasing trend in the past 51 years, while the precipitation and wetness index had a weak increasing trend, but the increasing trend was not obvious, which indicated that the climate trend of Mulei county in spring and summer had changed to warm and dry. The frequency of light drought in spring was higher than that in summer, and the frequency of moderate drought and severe drought in summer was higher than that in spring. The mean temperature, precipitation and relative humidity index of spring and summer all changed abruptly. According to the wavelet power spectrum test, most of the temperature, precipitation and relative humidity index in spring and summer had the scale variation period of 2~4 years. The periodic signal energy in time scales above 4 years and below 2 years was weak, and the significant variation period was mainly concentrated in the periodic oscillation around 3 years. The analysis of meteorological influencing factors of relative humidity index showed that the change of relative humidity index in spring and summer in Mulei county was caused by the comprehensive action of several meteorological factors, but precipitation, relative humidity and air pressure were the main meteorological factors that lead to the change of relative humidity index in spring and summer in the study area.

Key words: drought, humidity index, potential evapotranspiration, wavelet power spectrum, correlation analysis