Evaluation of water resources allocation scenarios of Mahabad basin under the influence of climate change using the WEAP model

Extended Abstract
Introduction: Climate change is one of the fundamental challenges of mankind in the last century and the coming years, which affects the status of water resources at the global level, especially at the scale of the watershed. In addition, climate change affects the hydrological cycle at the basin level and thus the management of water supply and demand. The Intergovernmental Panel on Climate Change (IPCC) emphasized that climate change is an inevitable phenomenon. Therefore, it is necessary to estimate water demand sites under the influence of climate change and evaluate different climate scenarios. Several software and models have been developed to estimate the effects of climate change and integrated management of water resources at the watershed level, among which we can mention the Water Resources Planning and Management System (WEAP).
By using the WEAP model, it is possible to investigate, manage, and allocate different policies for the optimal use of water resources under the influence of different management scenarios, including investigating the impact of climate change on the amount of water allocated to different supply and demand sites in Therefore, according to the importance of the topic in this research, the evaluation of different climatic scenarios of the Mahabad watershed was done.

Materials and methods: In this research, IPCC data were extracted under two scenarios RCP 4.5 and RCP 8.5, and then in order to use the data extracted in the study area, these data were used using the LARS_WG model with a smaller scale. In the following, the IHACRES model has been used to simulate rainfall-runoff in the future period in the study area. The outputs of the IHACRES model were introduced as the input of the Weap model, which is a comprehensive and integrated model in water resources. Then, the impact of climate change on supply and demand sites under different climate scenarios was simulated using the Weap model.
Results: In this study focused on Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) scenarios (RCP4.5 and RCP8.5) for 2020–2039 were used. The results obtained in the mentioned scenarios for the statistical period of 2020-2039 show a decrease in precipitation and an increase in temperature. In order to estimate the productive runoff of the basin under the influence of climate change, the IHACRES rainfall-runoff model was used and the performance of the model in the study area was evaluated with correlation coefficient (R) and bias error. It was found that in the calibration and validation period, the correlation coefficient and bias error were 72%, 0.08, 69%, and 0.59, respectively, which shows the acceptable performance of the model in the region. In the following, the outputs of the IHACRES model were introduced as input to the WEAP model and it was determined that with the priority of allocating one for the drinking site and two for the agricultural site of the MIROC 8.5 scenario, the highest amount of unmet demand with the amount of 121.4 million cubic meters, especially for the year 2039 will have. On the other hand, the GFDL 4.5 scenario will have the highest reliability with 72% volume reliability and 42% time reliability.

Conclusion: By examining the results, it can be concluded that according to the MIROC 8.5 scenario, the amount of rainfall will decrease by 4.8% compared to the observation period. This reduction trend was also observed in three other scenarios. Then, using the IHACRES model, the monthly average amount of flow for the periods of 2020 to 2039 was produced and it was observed that the amount of runoff produced by the model will decrease from 2036 onwards. In the following, the runoff produced by the IHACRES model as the input of the simulator-optimizer modelWEAP entered. Then, the information related to climate change was checked under four scenarios and it was found that the highest unsupplied water needs for drinking sites considering allocation priority one and agriculture with priority allocation two are related to the MIROC 8.5 scenario with the amount of unsupplied demand of 121.4 million. Is cubic meters. Of course, it is worth mentioning that in this study, underground water supply and water allocation to the industrial sector have not been modeled.

Keywords: Integrated water resources management, Climate Change, IHACRES, WEAP, Mahabad river basin.