The Trend of Changes in Relative Humidity in Razavi Khorasan Province, Northeast Iran

The present study was conducted to examine the changes in monthly, seasonal, and annual trends in relative humidity of 13 meteorological stations in the Razavi-Khorasan Province from the beginning of the statistical period of each station until 2021. The study area includes Dargaz, Fariman, Golmakan, Gonabad, Kashmar, Khaf, Neyshabour, Mashhad, Quchan, Sarakhs, Sabzevar, Torbat-e Jam, and Torbat-e Heydarieh counties. Parametric linear regression and the nonparametric Mann-Kendall (MK) test were used to detect trends in relative humidity. The majority of stations have shown decreasing trends at 5% significance level in relative humidity in different time scales, and only in two stations, Quchan (June, December, and autumn season) and Sarakhs (autumn season), the relative humidity showed an increasing trend at 5% significance level. A decrease in monthly mean relative humidity for six stations has been found in the range of 0.7 to 3.5 percent/decade, while an increase for Quchan station 1.9 to 2.6  percent/decade was observed. In addition, most of the studied stations have experienced a decrease in relative humidity on a seasonal and annual scale. A decrease in Seasonal mean relative humidity for six stations has been found in the range of 0.6 to 2 percent/decade, while decreases in annual mean relative humidity stations ranged from 0.9 to 1.6 percent/decade. The results of this research indicate a decreasing trend in the average monthly, annual and seasonal relative humidity during recent years.