dc.description.abstract
The climate change is expected to have significant impacts on the water resources in Afghanistan, which could exacerbate existing challenges related to water availability, water quality, and water management in the future. Therefore, this study investigated the impact of climate change on water availability in Upper Kabul River Basin (UKRB) in Afghanistan by analyzing the past and future streamflow dynamics and hydrology related parameters (e.g., water balance components). A hydrological model was developed in UKRB using the Soil and Water Assessment Tool (SWAT) from 2009-2019, calibrated from 2010-2016 and validated from 2017-2018. The model was built, calibrated and validated on daily and on monthly time intervals to provide a comprehensive analysis of the model’s accuracy. The performance of SWAT hydrological model is done by comparing the simulated results to the observed runoff in the Upper Kabul River Basin. SWAT was capable of estimating surface runoff with satisfactory to very good accuracy in 6 observation station across the UKRB during calibration and validation. Four regional climate models (RCMs) were used to project the climate change impact scenarios for the baseline (1986-2005), and future periods of 2030-2049 (hereafter 2040s), and 2080-2099 (hereafter 2090s). The future hydrology projections were built under RCP4.5 and RCP8.5 scenarios. The precipitation and temperature from the RCMs were bias corrected using three bias correction methods including the linear scaling (Ls), delta change (Dc) and empirical quantile mapping (Eqm). The bias corrected results in the baseline period were validated with APHRODTE precipitation and temperature data which is used as observations in the absence of in situ measurements. The precipitation and temperature outputs from bias correction methods were analyzed based on monthly, seasonal and annual intervals, and then the outputs from the linear scaling method were used in SWAT model for further climate change impact analysis.
The results indicated that all three bias correction methods improved the raw data of climate model outputs (RMCs), reduced the biases in precipitation and temperature variables based on APHRODITE datasets. However, the outputs from linear scaling performed better than empirical quantile mapping in capturing the distribution of precipitation, maximum temperature (Tmax) and minimum temperature (Tmin) in the historical period. Therefore, the Linear method was selected for further water availability assessment in the study area. According to the bias correction results, under the RCP4.5 scenario, the annual temperature is expected to increase by 1.9 °C in the 2040s and 2.3 °C in the 2090s. However, under the RCP8.5 scenario, the increase in mean annual temperature is projected to be more severe, with an increase of 3.1 °C in the 2040s and 6.1 °C in the 2090s. In addition, this study also examined how the extremes in temperature and precipitation might change in the future, specifically looking at six indices: annual total wet day precipitation (PRCPTOT), extremely wet days (R99p), monthly minimum value of daily minimum temperature (TNn), monthly maximum value of daily maximum temperature (TXx), warm nights and warm days over the course of the 21st century (2006-2100) in UKRB.
Results showed that temperatures increased in all seasons, with earlier peaks occurring in June instead of July in both periods of 2040s and 2090s. The results also show that, there was a significant increase in extremes of maximum and minimum temperature’s trend indicating that the future temperature is getting hotter. The future mean annual precipitation observed to be increase in the 2040s and 2090s compared to the baseline, however, an insignificant decreasing trend of annual precipitation observed during 2006-2100. The future mean annual precipitation will increase by 5 % in 2040s and 1 % 2090s under RCP4.5 over the study area. Moreover, under RCP8.5, the mean annual precipitation is expected to increase by 9 % in 2040s and almost + 2% in 2090s compared to the baseline. The annual spatial precipitation changes range from -3 % to +27 % in the 2040s and from -8 % to + 17% in the 2090s under RCP4.5. Similarly, under RCP8.5, it ranges from -3 % to +44 % in the 2040s and from -10 % to +27 % in the 2090s. The future hydrological results show that there will be an increase in mean annual runoff and mean annual total water yield in the 2040s and 2090s compared to the baseline period in UKRB. The results of our study also revealed a backward shift in the annual discharge peaks from May and June to March and April in Tang-i-Gulbahar and Shukhi stations, while in Tang-i-Saidan station, the runoff peak shifted from April to March in both periods of 2040s and 2090s in UKRB due to climate change. The results also show that there has been a significant increase in the future actual evapotranspiration (ET) and potential evapotranspiration (PET) in the UKRB under both RCP4.5 and RCP8.5 scenarios. However, decreases in mean annual snowfall, snowmelt, sublimation, percolation and ground water recharge is expected in the future under both RCP4.5 and RCP8.5 scenarios. The decrease in snowmelt and glacier melt could also lead to changes in the timing and volumes of river flow which can impact the water availability for agriculture, urban use, and hydropower generation. Overall, this study contributes to the growing body of knowledge on climate change impacts on water resources and emphasizes the need for continued research in this field.
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