| The global hydrological cycle is susceptible to climate change,particularly in developing countries including Pakistan,due to inappropriate management of precious freshwater resources.The purpose of this research work was to use Soil and Water Assessment Tool(SWAT),based on GIS-hydrological modelling,to analyses the variability in temperature and rainfall and their impact on streamflow in Soan River Basin.At first,a trend analysis was done to determine and confirm the climate variability in the study area for the years of 1991-2017.Secondly,mutation analyses were done to determine sudden changes in climatic and hydrological parameters.The CNRM-CM5 was selected as appropriate model due to higher coefficient of determination(R2)value for future prediction.Using the outputs of the CNRM-CM5 model,future climate change scenarios were shaped using the linear scaling method under two representative concentration pathways(RCP4.5 and 8.5).Using a calibrated SWAT model,future streamflow’s were also predicted based on a defined future climate change scenario.Maximum temperature and runoff decrease,while average temperature,minimum temperature,and rainfall going on increasing on annually basis.Results of this study showed that there was a significant increasing/decreasing trends from 1991-2017 on annual basis for maximum(Tmax),minimum(Tmin)and average(Tavg)temperatures with magnitude of-0.0460C/10 a,0.3930C/10 a,and 0.1420C/10 a,respectively.The negative sign shows that trend is decreasing and positive sign shows that,trend is increasing.The annual rainfall showed a significant increasing trend on annually basis of 1.6 mm/10 a.The runoff showed a decreasing trend on annually(-1.43 m3.sec-1/10a).Impact of urbanization/human activities on runoff is more than temperature,rainfall,and forest.Sudden changes in temperatures,rainfall and runoff were observed in 1997 and LUCC(specifically residential and forest area)were observed for 2003-2013.The MLR’s coefficients for temperatures,rainfall,and residential and forest area of 0.145,0.020,0.903,and-0.301 were observed against the significance p-values of 0.153,0.847,and 0.683,respectively.These results shows that human interventions have more impact on runoff rather than temperature and precipitation and all parameters shows positive impact except forest because it shows a negative impact on runoff.Maximum and Minimum temperature shows increasing trend,while rainfall and runoff show decreasing trend under both scenarios RCP4.5&8.5.The results showed that average annual precipitation for Rawalpindi,Islamabad,and Murree will be decreased by 43%,34%,and 30% under RCP4.5 and 51%,35%,and 31% under RCP8.5 respectively,in early to late century.The average annual maximum temperature will be increased by 3.73°C,4.12°C,and 1.33°C,and average annual minimum temperature will be increased by 3.59°C,3.89°C,and 2.33°C,under RCP4.5 scenarios and average annual maximum temperature 3.65°C,4.07°C and 1.4°C,and average annual minimum temperature by 3.52°C,3.42°C and 2.8°C,respectively in Rawalpindi,Islamabad,and Murree in early to late century under RCP-8.5.Consequently,the average annual stream flow will be decreased in future from 5 m3/sec to 7 m3/sec under RCP4.5 and 8.5,respectively till 2095.In conclusion,these results will help to find out the impact of CC on small water regions in the RCPs by using small scale climate projections.This study also suggested that policies for the agricultural and environmental sectors that must consider the decreasing and irregular pattern of rainfall,the tendency toward rising temperatures,and the maintenance of a balance between agricultural and residential areas in Soan river basin. |
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