LAUSR

Intense industrial activity has led to an increase in greenhouse gas concentration in the Earth’s atmosphere over the past few decades, whereby the climate change phenomenon has been recognized. Increasing greenhouse gases have been changing patterns and trends of extreme climate variables that are of great importance in agriculture, water resources, and environmental hazards. In the present study, the changes and trends in climate extremes of temperature and precipitation were evaluated based on various extreme-related indices over Iran. For this purpose, both daily temperature and precipitation data of 76 synoptic stations were selected for trend analysis throughout Iran during the period 1981–2010. The nonparametric Mann-Kendall trend test and Sen’s slope estimator are used to investigate the trends in the selected data sets. The results of 11 extreme temperature-related indices showed, in general, warm indices such as the number of warm days (TX90p), warm nights (TN90p), and warm spell duration (WSDI) had an increasing trend whereas trends in cold indices such as the number of cool days (TX10p), cool nights (TN10p), and cold spell duration (CSDI) decreased. The monthly maximum value of daily maximum (TXx) and minimum (TNx) temperatures increased by 0.3 and 0.4 °C/decade on average, respectively; and the monthly minimum value of daily maximum (TXn) and minimum (TNn) temperatures increased by 0.1 and 0.3 °C/decade, respectively, on average during the study period. In the case of the extreme precipitation-related indices, the results indicated both a decreasing trend in precipitation amount and intensity, and an increasing trend in the number of consecutive dry days (CDD) at most of the selected stations. Surveys demonstrated that the western, northern, and northwestern regions of Iran were most affected by the risk of climate extremes. Thus, these extreme changes will make people more vulnerable to natural hazards and make proper management in the face of climate crises more necessary.