Abstract: The monthly meteorological data were observed during the period of 1953-2013 at Jinghe and Wusu meteorological stations in the Ganjiahu Haloxylon Nature Reserve in Xinjiang, on which the monthly potential evapotranspiration (ET₀) and the humidity index (I_a) were calculated by the Ivanov method. The seasonal and annual changes of surface dry/wet conditions and their main impact factors were analyzed. Results showed that the average values of ET₀ in winter half year, summer half year and the whole year during the past 60 years were 298 mm, 1 107 mm and 1 407 mm respectively. The ET₀ decreased in winter half year but increased in summer half year and the whole year. The I_a decreased in spring and summer but increased in autumn, winter and the whole year. Based on the climate zoning standards related to I_a, the nature reserve is a semiarid region in spring, extremely arid or arid region in summer and autumn, and humid and sub-humid region in winter. I_a was positively correlated with precipitation, vapor pressure and relative humidity, and negatively correlated with wind speed, air temperature and sunshine duration. I_a was influenced maximally by relative humidity, followed by sunshine duration, air temperature, vapor pressure and precipitation, and minimally by wind speed.

Key words: humidity index, potential evapotranspiration, dry/wet conditions, Ganjiahu Haloxylon Nature Reserve, Xinjiang