Impact of Climate Change on the Monthly Runoff of a Semi-arid Catchment: Case Study Zarqa River Basin (Jordan)

Abstract

In this paper, the long-term hydrological responses (runoff and actual evapotranspiration) of a semi-arid basin to climate changes were analyzed. This basin is the Zarqa River (Jordan). The climate changes were imposed with twelve hypothetical scenarios. Two of these scenarios were based on the predictions of general circulation models (GCMs), namely the Hadley and MPI models. The other ten scenarios are incremental scenarios associated with temperature increases by +2C and +4C and changes in precipitation of 0%, +10%, +20%, -10%, and –20%. These scenarios were used as a basis for observing causal relationships among runoff, air temperature, and precipitation. The Surface-Infiltration-Baseflow (SFB) water balance model that was developed by Boughton (1984) was used for observing these causal relationships. Firstly, areal precipitation and potential evapotranspiration of the basin are estimated based on the observed meteorological and hydrological data. The monthly runoff simulations are then predicted through the application of the SFB model. Seven years of meteorological and hydrological data are used for calibrating the model, and another Seven years of the record are used for model validation. The global optimization technique known as Shuffled Complex Evolution (SCE) method is used to obtain the optimal parameters of the SFB model. The model performed well for the Zarqa River for which the coefficient of determination was 0.78. The average monthly runoff from the model compared well to the observed average runoff. The error of the observed and simulated streamflow is within acceptance limit and found to be around 18 percent. The model performance in the validation stage is reasonable and comparable to those of the calibration stage. Both sets of climate change scenarios resulted in decreases in monthly runoff. Differences in hydrological results among all climate cases are due to wide range of changes in climate variables.

Keywords

• Climate change, Optimization, Rainfall-runoff modeling, Incremental scenarios, Calibration, Validation