Spatiotemporal changes in aridity and the shift of drylands in Iran

Abstract

The spatial and temporal changes in annual and seasonal aridity, the shift of land from one arid class to another and the effect of this shift on different landuses in Iran during 1951–2016 have been assessed in this study. The monthly rainfall data of global precipitation climatology center (GPCC), and the monthly mean temperature and potential evapotranspiration (PET) data of climate research unit (CRU) having a spatial resolution of 0.5° were used for this purpose. The novelty of the study is the assessment of the significance in the shift of arid land between 1951–1980 and 1987–2016. Besides, the association of rainfall and temperature with aridity in different arid zones were assessed to understand the driving factors of the shift of arid lands. The results revealed an increase in annual and seasonal aridity in Iran, which caused expansion of arid land. The most remarkable changes include conversion of 4.84% semi-arid land to arid land due to an increase in annual aridity, shift of 4.84% arid land to hyper-arid during summer and 6.45% semi-arid land to arid during winter. However, only the expansion of semi-arid land to dry-subhumid land was found statistically significant. Analysis of results revealed different contributions of rainfall and temperature in the expansion of different classes of arid lands. The decrease in rainfall was the cause of the increasing aridity in the arid and semi-arid region, while the increasing temperature was found to play a major role in increasing aridity in the humid region. The overlapping of landuse map on aridity shift map revealed that the rangelands and farmlands in the north and the northwest were more affected by the expansion of aridity which might have severe consequences on agricultural production and food security of the country.