Assessment of climate change over Iran: CMIP5 results and their presentation in terms of Koppen-Geiger climate zones

Climate change is arguably one of the most important challenges affecting different aspects of human life and the environment. The current research is an effort to assess the possible impact of climate change on precipitation, temperature, and consequently climate zones over Iran, based on the Koppen-Geiger climate classification scheme. To this end, monthly mean values of precipitation totals and air temperature from 149 synoptic stations during 1971-2015 as well as output from 17 Earth System Models of the CMIP5 (Coupled Model Intercomparison Project Phase 5) under two emission scenarios, RCP4.5 and RCP8.5, over the twenty-first century were taken into consideration. The results obtained by the ensemble mean of the 17 CMIP5 models under RCP8.5 scenario indicated that the annual mean temperature is expected to increase significantly by 1.9 and 3.3 degrees C for the periods of 2041-2070 and 2071-2100, respectively. For precipitation, results showed that the annual mean precipitation over the country is expected to decrease under both RCP scenarios relative to the baseline period (1971-2015) between - 5.4% by 2041-2070 under RCP4.5 and - 9.5% by 2071-2100 under RCP8.5. Monthly precipitation regimes are expected to change across the country, especially in the Caspian Sea coastal regions and in Alborz mountain ranges. The Koppen-Geiger climate classification map of Iran is derived for the period 1971-2015 and compared to existing global Koppen-Geiger climate classification maps. Also, computing climate types of Koppen-Geiger climate classification based on averages from three climatic periods (1971-2015, 2041-2070, and 2071-2100) showed that the area of arid-desert and arid-steppe climate classes (BW and BS) and the area of moderate and snow climate classes (Ds and Cs) are expected to increase and decrease, respectively. The results of this study could impact on strategic planning in agriculture and water resources, and thus consequently affecting the economy of Iran.