Drought trends projection under future climate change scenarios for Iran region

in other stations such as Ghom with a hot climate and Tabriz with a cold climate. In regard to wet periods, the results are the same, i.e. the highest frequency of wet periods is related to cold climates, whereas the lowest belongs to warm climates. However, the duration of dry periods in warm climates is longer than that of cold climates. The information given for Rasht and Gorgan in comparison with Zahedan and Ahvaz can confirm these declarations. Sobhan et al. (2019) also reported that the southern stations of Iran are more exposed to drought than others. It should be mentioned that uncertainty in the prediction of future events is inevitable, it is significantly affected by the type of data used in terms of quality and quantity aspects, and also the structure of downscaling model [36, 49]. Regarding the data, using dataset with no missing data will reduce uncertainty, which was done in this study. Apart from that, the SPEI index assimilates more factors to quantify drought characteristics which affects less uncertainty [25]. From aspect of model, considering the calibration results, it can be claimed that the present model could discover connections of weather parameters with high accuracy, thus the perfor- mance of the model is acceptable. Moreover, different scenarios provided a chance to consider different assumptions in prediction which was compared. There is no hesitation that removal of uncertainty in modelling is impossible, nevertheless, the above-mentioned reasons can con- firm reliability of the findings in this study.

For more understanding, the monthly changes of PET and precipitation predicted under the A2 scenario for each station are provided in Fig 5. Fig 5 presents the area charts of PET and precipitation in a monthly time scale for the next 102 years. It seems to be crystal clear that for the vast majority of stations, the area of PET is signifi- cantly more than the area of precipitation. The most difference can be seen in the middle months of the year (e.g., in warm months), which is a logical and rational consequence. These findings are consistent with the report of [50], who concluded that the magnitudes of PET in Iran increases from January to July, then drop from August to December, and all stations reach their maximum levels in July. Since the highest temperature takes place in warm months, subsequently the amount of PET would increase as warming accelerates. However, the proba- bility of precipitation occurrence would drop. These findings can be observed in regions with hot climates such as Semnan, Yazd, Zahedan, and Kerman which are located in the southern part of Iran. [37] also declared that the southern regions of Iran are more severely affected by drought. These results refer to the importance of suitable water management in warm months and especially preserving and harvesting precipitation during the months with high precipita- tion. Contrary to these regions, the amount of precipitation (110.80 mm/month) in Rasht is approximately 26 percent more than the PET (87.51 mm/month). These consequences are in line with the findings of [51].

In general, it can be concluded that water shortage in warm climates would be much more serious than in other climates. Despite insufficient precipitation being the principal cause of water scarcity and drought, non-meteorological drivers such as rapid population growth, poor water resource management, and unsuitable cropping patterns also play critical roles [51]. 4. Conclusion Evaluating the amount of precipitation and PET for the base period and the next 102 years depicted that the highest PET and the lowest precipitation are related to the southeast of the studied area. Prediction of drought by SPEI under climate change scenarios indicated that the vast majority of stations will be involved in drought events. However, regions with hotter cli- mates will experience more intensive drought. Comparing forecasted drought under the A2, A1B and B1 scenarios showed that 19.23% of months over the next 102 years under the A2 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 20 / 24