Climate Change Effect on Sediment Yield at King Talal Dam (Jordan)

Abstract

With a yearly precipitation of 200 mm in most of the country, Jordan is considered one of the least water-endowed regions in the world. Water scarcity in Jordan is exacerbated by growing demands driven by population and industrial growth and rising living standards. Major urban and industrial centers in Jordan including the Capital Amman are concentrated in the northern highlands, mostly contained within the boundaries of the Zarqa River Watershed (ZRW). The ZRW is the third most productive basin in the greater Jordan River System. King Talal Dam was built few kilometers upstream of the Zarqa-Jordan confluence to regulate its input mostly for the benefit of agricultural activities in the Jordan Valley. King Talal Dam (KTD) is the most important one in Jordan. It lies at the outlet of Zarqa River watershed (ZRW). This dam has a capacity of 86×10⁶ m³, which serves irrigation purposes in the Jordan Valley. However, the dam suffers from accelerated annual sedimentation.

Concerns regarding the sensitivity of the ZRW to potential climate change have prompted the authors to carry out the current study. The methodology adopted is based on simulating the hydrological response of the basin under alternative climate change scenarios. The Soil and Water Assessment Tool (SWAT) is a powerful time-variable hydrologic model that has rarely been applied in arid environments. In this paper, the performance of SWAT in the semi-arid Zarqa River watershed (ZRW) was assessed. The SWAT model was calibrated for Zarqa basin using records spanning from 1980 through 1994. The model was validated against an independent data record extending from 1995 through 2002. Calibration and verification results were assessed based on linear regression fitting of monthly and daily flows. Monthly calibration and verifications produced good fit with regression coefficient r values equal to 0.928 and 0.923, respectively.  Annual volume predictions correlated well with measured flow in both the calibration (r = 0.94) and validation (r = 0.93) periods.  For model validation the simulation results were compared to the measured values over 12 years period.  Good agreement was obtained in some of the years.

Utilizing the SWAT modeling environment, scenarios representing climate conditions with ±20% change in rainfall, and 1^oC , 2^oC and 3.5^oC increases in average temperature were simulated and assessed. Unique relationship between the percent change in precipitation scenarios and the parallel change in sediment yield has been studied at different change in temperature to evaluate the degree of sediment sensitivity with temperature and precipitation.

The study shows that climate warming can dramatically impact runoffs, groundwater recharge and sediment yield in the basin. However the impact of warming can be greatly influenced by significant changes in rainfall volume.

Keywords: Zarqa River, Climate change, Sediment, SWAT