Forecasting Rainfall in Different Climatic Regions of Iran Using the LARS WG7 Climate Model

Bagheri Khaneghahi, Marzieh; Hezarjaribi, Aboutaleb; Kamali, Mohammad Ismaeil; Zamani, Fatemeh

doi:10.22091/wrcc.2025.11744.1008

Forecasting Rainfall in Different Climatic Regions of Iran Using the LARS WG7 Climate Model

Document Type : Original Article

Authors

¹ Ph.D. Student, Department of Water Engineering, Faculty of Water and Soil, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

² Department of Water Engineering, Faculty of Water and Soil, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

³ Department of Soil and Water Research, Agricultural and Natural Resources Research and Education Center of Golestan Province, Gorgan Agricultural Research, Education and Promotion Organization, Gorgan, Iran.

⁴ Department of Computer Engineering, Faculty of Electrical and Computer Engineering, Noshirvani University of Technology, Babol, Iran.

10.22091/wrcc.2025.11744.1008

Abstract

Abstract
Objective: The objective of this study is to evaluate the performance of the downscaling model LARS-WG7 in projecting precipitation across six major Iranian cities: Gorgan, Mashhad, Shiraz, Ahvaz, Kermanshah, and Urmia.
Method: For this purpose, precipitation data from the statistical period 1991-2020 were considered as the baseline. Subsequently, the model was employed to predict precipitation changes for three future periods (2021-2040, 2041-2060, and 2061-2080) under three climate scenarios of HadGEM3 (SSP585, SSP126, SSP245).
Results: The results indicate that precipitation under the climate scenarios is projected to be lower than the baseline in certain months of all future periods. However, the trend of mean annual precipitation generally shows an increase compared to the baseline. Exceptions were observed in Urmia, where precipitation exhibited a decreasing trend during 2021-2040 (under SSP126) and 2061-2080 (under SSP585), and in Mashhad, where a decreasing trend was detected during 2061–2080 (under SSP585).
Conclusion: The findings revealed that the largest percentage difference in precipitation (42.66%) between the baseline and future periods (under SSP585) occurred in Ahvaz, while the smallest difference (4.16%) was observed in Urmia. Overall, both monthly and annual precipitation trends varied across the future periods depending on the applied SSP scenarios.

English Extended Abstract

Introduction
Water resources, agriculture and environment are among the important factors affected by climate change. Therefore, it is more important to examine the process of changes in parameters such as temperature and precipitation to know the future climate in order to plan and make management decisions.
The purpose of this study is to evaluate the microscale model (LARS-WG7) in forecasting rainfall in the cities of Gorgan, Mashhad, Shiraz, Ahvaz, Kermanshah and Urmia.

Method
In this research, first, the daily rainfall information for the statistical period from 1991 to 2020 related to the synoptic stations of the studied cities was obtained from the National Meteorological Organization. Then, the LARS WG7 climate model was used in order to predict the precipitation of future periods.
After sorting the daily rainfall data of the study stations in the Notepad file and selecting the HadGem3 model and the SSP scenarios and future periods considered in LARS WG7, the software was implemented for the study stations. In the first step, the modeled data were compared with the observed data. In the next step, with the help of the base period data, the data of the future periods (2021-2040, 2041-2060, and 2061-2080) were produced under different scenarios (SSP126, SSP245, and SSP585), and finally, the changes in precipitation in the future periods compared to the base period were investigated.

Results
The results showed that the amount of rainfall under the climate scenarios in all future periods in some months of the year is less than the base period. The trend of changes in the average annual rainfall in future periods is increasing compared to the base period. But only in Urmia city, the future period of 2021-2040 (under the SSP126 scenario) and the future period of 2061-2080 (under the SSP585 scenario) compared to the base period showed a decreasing trend of rainfall.
In the city of Mashhad, the future period of 2061-2080 (under the SSP585 scenario) showed a decrease in rainfall compared to the base period. Also, the results indicated that the highest percentage of difference in rainfall amount (42.66%) between the base and future period (under SSP585 scenario) belongs to Ahvaz city.
The lowest percentage difference in rainfall amount (4.16%) between the base and future period (under SSP585 scenario) belongs to Urmia city. The trends of rainfall changes (monthly and yearly) in the future periods were variable under different SSP scenarios.

Conclusion
According to the obtained results, it was found that the climatic conditions in the coming periods will be significantly different from the current conditions and in the coming years, the studied cities will face more rainfall. Changing the precipitation pattern in the future in cities can be caused by atmospheric instability and global warming. With the increase in temperature, the polar ice melts and leads to the rise of the water level of the seas and rivers and finally leads to climate changes and increased rainfall.
The increasing trend of precipitation changes in the coming periods can lead to surface runoff and soil erosion in the future. Therefore, managing the crisis of urban floods in the coming years will be an important and necessary measure.
Also, managing the optimal use of water in the agricultural sector for rainfed crops, choosing the type of crop and paying attention to the crop calendar according to the amount of precipitation in different months of the year is more important than before.

Keywords

Main Subjects

Climate change

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