Investigating the climate change effects on annual average streamflows in the Euphrates-Tigris basin using the climate elasticity method

This study was conducted to investigate the response of streamflows (Q) to changes in precipitation (P), potential evapotranspiration (E-p) and drought index within the Euphrates-Tigris basin. For this purpose, 37 sub-basins that are not affected by dams were identified within the basin. Here, the sensitivity of annual average streamflows to precipitation, E-p and drought index was evaluated by the climate elasticity method proposed by Schaake [1]. With this method, the average values of the precipitation and E-p sensitivity coefficients of the streamflow (epsilon(P) and epsilon(Ep), respectively) throughout the basin were calculated as 1.50 and -0.50, respectively. Therefore, it is observed that a 10% increase (decrease) in precipitation would lead to an average increase (decrease) of 15% in streamflow, on the other hand, a 10% increase (decrease) in Ep would result in an average decrease (increase) of 5% in streamflow across the basin. Moreover, the average value of sensitivity coefficient of streamflow to drought index (epsilon((sic))) was determined as -0.47, which means that a 10% increase in the drought index will result in an average decrease of 4.7% in streamflow within the basin. Additionally, it is observed that there is a nonlinear inverse correlation between the climate change sensitivity coefficients (i.e., epsilon(P), |epsilon(Ep)| and |epsilon((sic))|) and the flow coefficient (Q/P) values of the sub-basins indicating that the decrease in streamflow would increase the sensitivity of streamflow to climatic changes. Finally, it was determined that there exist relative increases in epsilon(P), |epsilon(Ep)| and |epsilon((sic))| values from high to low elevations across the basin.