Moisture index for Iran: Spatial and temporal analyses

Moisture indices, which account the balance between inputs and outputs of water, are typically used to determine the moisture conditions and the magnitude of water deficiency in a given area. This work studies the moisture conditions of Iran using the revised Thornthwaite moisture index, a ratio of evapotranspiration to precipitation, over the period of 1966–2005. Long-term trends in the moisture index were assessed by the Mann–Kendall test, the Senʹs slope estimator and the Mann–Kendall rank statistic. According to the moisture index, arid and semiarid environmental conditions where the demand for water exceeds the water supply are dominant over the country. The results conclusively show that the significant trends in the moisture index are infrequent and found only at 8 out of the 41 study stations. The significant downward trends of the moisture index at Gorgan, Kermanshah, Khorram-Abad, Khoy, Sanandaj, Tabriz and Zanjan stations located in the north, northwest and west regions of Iran began in 1995, 1996, 1996, 1989, 1997, 1988 and 1986, respectively. Contrary to that, the significant upward trend at Dezful station started in 1973.