Analysis of spatial changes of extreme precipitation and temperature in Iran over a ۵۰‐year period

Abstract

This research was carried out to determine whether the changes in precipitation and temperature trend in Iran are attributed to climate change or natural climate variability. The trend and its magnitude with the climatic extremes indices considered by Expert Team on Climate Change Detection and Indices were analysed based on the quality‐controlled daily data of 37 meteorological stations by nonparametric Mann–Kendall test and Sen's slope method from 1966 to 2015. Results indicated that TXx, TNn, the average maximum, and minimum temperature indices have increased with a significant trend in most parts of Iran. The minimum temperatures (TNn and annual Tmin) were increased more rapidly than maximum temperatures (TXx and annual Tmax) and rising temperatures have occurred in northern latitude and western regions more than elsewhere. As a result, the temperature increase leads to changes in seasons and season length; and reduces the growing season of a variety of plants. On the other hand, the MK test detected an insignificant trend of PRCPTOT, R10, R20, and R95p, in most of the stations. The observations showed that CDD had no trend and consecutive wet day had a significant decreasing trend; subsequently, SDII has increased. Besides, RX1day and RX5day indices have gradually decreased, so that Max5‐day has not shown any trend during 1966–2015. Wet day precipitation as well as number of heavy and very heavy precipitation days tend to decrease across the study area. The west and northwest of the country have a more significant trend of precipitation indices. Overall, temperature extreme indices are increasing and precipitation indices are decreasing, which may largely be due to the natural climate variability or urban heat island. Given that climate change is a trans‐regional phenomenon, it is important to examine the climate of neighbouring countries during the same period, as well. Generally, the findings could provide helpful information for agriculture and food security, water, and eco‐social‐environmental planners.