Investigation of Precipitation-Based Indices in the Mazandaran Region Under Climate Scenarios of the Sixth Report

Extended Abstract Background: One of the important effects of global warming is the increase in extreme atmospheric phenomena, the most important of which are sudden changes in temperature, excessive heat, abnormal cold, heavy rains and floods, drought, and dust caused by the drying up of wetlands. Changes in climatic components due to climate change have impacted the intensity and frequency of extreme rainfall events and, subsequently affecting society and the natural environment. Therefore, examining the future modifications of different precipitation indices is more necessary to implement management plans, especially for Iran, which needs progress in climate modeling studies aiming at improving knowledge about climate change and its effects on the whole country. In this study, changes in the trend and breaking point of rainfall-based indices were studied using the CMIP6 series model under three optimistic, medium, and pessimistic scenarios in Mazandaran province for two periods: the near future (2021-2060) and the far future (2061-2100). Methods: In this research, the spatiotemporal trend and breaking point of the precipitation in Mazandaran province (15 stations) were investigated in the future period from the precipitation data of SSP scenarios (126, 245, and 585) in the two 2021-2060 and 2061-2100 periods.  Using the R-Climdex software in the R software environment, the precipitation limit indices were determined for different scenarios and periods. Then, the trend and breaking point were examined using the Mann-Kendall, Sen, and Pettitt tests. Precipitation indexes were defined by an expert group under the supervision of the World Meteorological Organization as limit indexes and climate change indexes. After receiving the output of models and their micro scaling, data were grouped in the future period based on three scenarios in all studied stations. The daily rainfall indexes were extracted using R programming developed by Zhang and Yang at the Canadian Meteorological Service Climatic Research Branch. Therefore, 11 and 16 indices out of 27 existing indexes were related to precipitation and temperature, respectively. Results: Under the optimistic scenario (SSP126), the indexes of the number of consecutive wet days, days with heavy rain, and very wet days in the eastern half of the province will increase significantly. Based on the pessimistic scenario (SSP585), the profile of wet days and the annual amount of rainfall will decrease in different areas of the province. In terms of the occurrence of the breaking point, the daily intensity of precipitation and wet days will have a breaking point in the order of increasing in the 2060s, rising in 2061, and decreasing in 2051 in the eastern half of the region only in the pessimistic scenario of the profile of consecutive wet days. Under the other scenarios, however, no sudden changes will be observed in the data series. According to the median scenario, there will be no changes in precipitation indexes regionally, and only the daily intensity index of precipitation will increase in a limited number of coastal stations in the near future. Under a pessimistic scenario, however, changes in limit indexes will often be reduced so that the index of the number of wet days (with 1 mm rainfall) will decrease in the near future in most parts of the province with high intensity. The annual amount of rainfall on wet days in coastal and western regions, as well as two indexes of the number of days with heavy and very heavy rain, will decrease in the high stations of the western areas. However, the risk of flooding events may be reduced in the near future, and the probability of widespread droughts increases due to the reduction of wetness profiles in pessimistic conditions. In the distant future, precipitation indexes will not change significantly, and only the number of days with heavy rainfall will decrease in the high areas of the eastern province. In terms of sudden changes, there will be no sudden change or significant breaking points in the data series of all the precipitation indexes until 2100 by moving toward an optimistic and median scenario. Moving toward a pessimistic scenario, there will be an incremental change point for indexing the number of consecutive days at a few provincial stations for the 2070-2060s. The daily intensity of precipitation and the number of wet days (with 1 mm precipitation) will also experience a sudden incremental change in 2061 and a decrease in 2051 in the eastern half of the province, indicating a sudden increase in the intensity of downpours and a reduction of the number of days with low rainfall. Conclusion: According to the results, it can be concluded that the study of the occurrence of severe meteorological events, including rainfall, as one of the main issues in the field of water resources, agriculture, and natural hazards in Mazandaran province, is necessary for long-term planning in various fields. Knowledge of the future perspective of extreme rainfall events can be used in soil, water, and agriculture management planning, especially in the economic development plans of the province.