Drought trends projection under future climate change scenarios for Iran region

each station. By this way, these three variables (Tmax, Tmin and precipitation) were simulated for the future periods. For the calibration of LARS-WG, two comparison statistics, mean bias error (MBE) and normal root mean square error (NRMSE) were applied, which are defined as [35]: NRMSE ¼ 1 n Pn i¼1 ðX YÞ2 � �0:5 �X ð6Þ MBE ¼ Pn i¼1ðX YÞ n ð7Þ where, X are the observed values and Y are the simulated values, �Xand �Y indicate the means of X and Y values respectively, n is the number of data. After a good calibration of the developed model for the base period, the mentioned climatic variables were predicted for the future periods considering three scenarios, A1B, A2 and B1. The assumption made by the B1 scenario relies on an endurable world, that is, quick changes in economic developments, advancement of human rights equality and a consideration to environmental protection. This assumption considers that greenhouse gas emissions can be controlled and a pollutant controlling programme will be in place for the industries. The assumption made by the scenario of A1B relies on a wealthy world with a quick economic development (about 3percent per year), decrement in population (about 27% per year), quick technological development, convergence of culture and economy and a principle decrease in regional differences. The assumption made by the scenario of A2 relies on the assumption of a separate world. Different cultural characteristics in various areas of the world are expected to cause differences in the change of climate parameters [36]. Hence, the climatic variables were

forecasted for three different periods (each having 34 years), 2011–2045, 2046–2079, and 2080–2112 under various scenarios. In the second step, the amount of PET was calculated by the Hargreaves-Samani (HS) method. Due to the fact that the SPEI considers both precipitation and temperature, thus applying a method based on temperature can reflect the impact of temperature, which is completely transparent in the HS. Moreover, through comparing influence of climatic Fig 2. Description of drought characterization. 1: Drought with highest severity, 2: Drought with the longest duration, 3: Drought with the highest intensity. https://doi.org/10.1371/journal.pone.0290698.g002 PLOS ONE Drought trends projection under future climate change scenarios for Iran region PLOS ONE | https://doi.org/10.1371/journal.pone.0290698 November 9, 2023 6 / 24