ارزیابی واکنش هیدرولوژیکی حوضه آبریز کیوی چای به تغییرات اقلیمی آتی با مدلSWAT

Abstract
Climate change has a direct impact on hydrological components and water resources and plays an important role in aggravating possible risks such as drought and floods. Therefore, it is necessary to investigate the effects of climate change on water components such as runoff. This study evaluates the effect of climate change on climatic parameters (temperature and precipitation) and the amount of runoff in Kiwi Chai basin from an environmental point of view. The hydrological model of the Soil and Water Assessment Tool (SWAT) was used to analyze the effects of climate change on the water resources of the Kiwi Chai basin, which is one of the Sefidroud sub-basins. Runoff simulation by applying climate change conditions for models (EC-EARTH, HadGEM2-ES, MIROC5, MPI-ESM) under two scenarios (RCP 4.5 and RCP 8.5) in three periods (2040-2021), (2041-2060), ( 2061-2080) and statistical analysis was performed to identify which climate model is more consistent with the changes in the mean and standard deviation of the historical series. An increasing trend in precipitation and a significant increase in average annual temperature were predicted in the early, middle, and late 21st century. The results of simulation of basin runoff with SWAT model also showed a significant decrease in basin runoff in future periods compared to the base period. These findings provide local water management authorities with useful information to aid decision-making in the face of climate change.
Introduction
The last century has seen a significant increase in greenhouse gas emissions. High concentrations of carbon dioxide and other greenhouse gases in the atmosphere increase the greenhouse effect and directly affect the global temperature (Verma et al, 2015). As a result, global warming has increased evaporation and transpiration rates and has led to changes in precipitation worldwide. Such global climate changes significantly affect the hydrological cycle and river flow regimes, especially at the basin scale (Zhang et al, 2016), which directly affect the ecosystem, water security and economic activities, mainly in agriculture, forestry and hydropower generation. Lays.Some consequences of climate change, such as increased extreme floods and droughts, may be inevitable (Chattopadhyay and Jha, 2016); Therefore, quantifying the impact of climate change on water availability is necessary for watershed management and also for formulating adaptation strategies to reduce its negative effects.So far, climate models have developed many effective tools for climate simulations in past and future periods. The fifth phase of the Coupled Model Intercomparison Project (CMIP5) includes more than 40 models and in them, a new set of release scenarios called Concentration Trajectory Representative (CCP) has been used and has produced valuable climate information for policymakers and the scientific community. (Falah Kalaki et al., 1400) RCP scenarios based on the amount of radiative forcing (watts per square meter) include 4 greenhouse gas emission scenarios RCP2.6, RCP4.5, RCP6.0, RCP8.5, which are introduced to simulate climate variables in the future period and have predicted an average increase in global temperature by 2100 compared to the last 30 years by an average of 2 degrees Celsius (Van Vuuren et al, 2011). Several researches have evaluated the impact of climate change on the hydrological cycle in Iran and other parts of the world. However, no studies have focused on the evaluation of flow changes in Kiwi Chai watershed. (Leta et all, 2016) in the study of the effects of climate change on the components of the water balance of the Hiya watershed, they concluded that the decrease in rainfall in the wet season and a slight increase in the dry season are the main factors of the overall decrease in the components of the water balance, and the flow of underground water is possible Due to the predicted precipitation and temperature changes, it will continuously decrease by 15% by the year 2100, which can have serious consequences on the existence of underground water in the basin. (et al, 2017 Reshmidevi) investigated the effects of climate change on the water balance of Malaprabha basin. The results show a slight decrease in the ratio of runoff, annual flow and groundwater recharge at the end of the century. It is also predicted that wet periods will decrease, while dry periods will increase in the future.Yan et al., 2018) in investigating the impacts of future climate change on the flow based on CMIP5 forecast in the Muon reservoir basin, concluded that the Muon basin will be warmer and wetter, as well as the average annual average temperature changes in the period (2035-2021). It will be more than 5.4% (0.6°C) and 12.5% (1.6°C) during the period (2065-2051). At the same time, the future flow and forecast of nitrogen loading will increase in the next two periods. (Bhatta et al. 2019) researched climate changes on the hydrology of the Himalayan river basin. They found that annual mean maximum temperature (+4°C) and minimum temperature (+5.5°C) would increase and precipitation would decrease (−4.5%) by the end of the 21st century under RCP8.5 scenarios. Ndhlovu and Woyessa, 2020) conducted a study on the impact of climate change on the water balance of Kabumpo River in South Africa. According to their findings, the future water balance of the basin under RCP4.5 will have little change compared to the current water balance of the basin, because the annual statistics show that the amount of rainfall will decrease by 1%, while the yield of water and runoff will increase by 5% and 6%, respectively
Methodology
The purpose of this study is to determine the impact of future climate changes on the river flow of Kiwi Chai basin. SWAT model was used to develop different scenarios. Under different climatic conditions in the future, especially with regard to rainfall and temperature, the response of the basin was evaluated. The impact of climate change on hydrology was analyzed in three different time frames: (2021-2040), (2041-2060) and (2061-2080). The 24-year period from 1994 to 2017 was used as the base period. The method used in this study includes the following steps: (1) configuration, calibration and validation of the hydrological model using SWAT (2) spatial and temporal data extraction of GCMs, exponential micro-scale of these data using Lars-wg6 software (3) analysis and Comparative evaluation of fine-scale GCM forecasts with respect to their ability to reproduce the historical climatology for GCM selection (4) to obtain results in SWAT for each scenario considered. (5) Assessing the impact of climate change in the basin by simulating new climate conditions in the calibrated SWAT model
Conclusion
The Kiwi Chai river basin is ecologically located in an area that ensures water supply for local communities and is also important in regional development through tourism, agriculture and horticulture. In the present study, the effects of climate change on meteorological variables (i.e. precipitation and temperature) and also on the main hydrological variables (surface runoff) have been analyzed. Future forecasts of precipitation and temperature of four GCMs (EC-EARTH, HadGEM2-ES, MIROC, MPI-ESM) were considered. After analyzing and comparing these predictions, the best model was selected based on its ability to reproduce the historical climate. The SWAT model is a conceptual and distributional model that was applied to quantify the impacts of future climate change on hydrological processes regionalized by HadGEM2-ES for the RCP 4.5 and RCP 8.5 climate scenarios. SWAT reasonably simulated the monthly flow despite the lack of data and the results were compared in the basin based on the base period data for future periods (2061-2080, 2041-2061, 2021-2040).The results of this analysis indicate an annual decrease of 15% (RCP 4.5) and 11% (RCP 8.5) of precipitation at the beginning of the century and 16% (RCP 4.5) and 11% (RCP 8.5) in the middle of the century and 19% (RCP 4.5) and 14 The percentage (RCP 8.5) at the end of the century is based on the base period (1994-2017). The mean annual temperature for the beginning of the century showed 15 and 33% increase, 25 and 33% increase for mid-century and 35 and 52% increase for the end of the century under RCP 4.5 and RCP 8.5 scenarios, respectively. The discharge simulated by the HadGEM2-ES model shows a decreasing trend in all three time periods compared to the base period. The largest decrease occurs in the hot months of the year, when the base discharge is low, which can be attributed to the decrease in precipitation and increase in temperature, followed by the increase in evaporation and transpiration. The long-term average observed discharge of the study area at the spa station was 3.08 and at Firozabad station 1.95 cubic meters per second, while in the time periods (2061-2080, 2041-2060, 2021-2040) at the spa station, respectively (0.02 , 0.03, 0.02) and in Firozabad station (0.04, 0.05, 0.04). The results show that the availability of water in the medium and long term is significantly affected, and therefore policies should be developed to adapt to climate change to ensure the environmental and economic sustainability of this region.
Keywords
climate change, water balance, hydrological modeling, swat