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An approach for estimation of the parameters of a macroscale land surface hydrology model is illustrated for the Global and Water Cycle Experiment (GEWEX) Continental Scale International Project (GCIP) large‐scale area southwest (LSA‐SW) which essentially comprises the Arkansas‐Red River basin. The macroscale land surface hydrology model parameters were estimated for 44 catchments within LSA‐SW with areas ranging from 180 to 7100 km2 using an automated search procedure. The catchment parameters were then linearly interpolated and overlaid on a one degree grid, which was used to represent the drainage network. The macroscale grid network model was run off‐line at a daily time step, forced by gridded station precipitation and potential evapotranspiration. The model‐generated long‐term mean streamflows were compared with observations (corrected for management effects such as reservoir storage and diversions) and were found to agree to within one percent for the Arkansas River and about two percent for the Red River. For both rivers, the model underestimates the seasonal peak streamflow in late spring, and overestimates the late summer and early fall minimum. Model‐derived evapotranspiration, spatially averaged over the entire Arkansas‐Red basin, was compared to evapotranspiration derived from an atmospheric moisture budget of the Arkansas‐Red River basin. On an average annual basis, for the period 1973–1986, the two agree to within one percent. The mean seasonal cycles for the two estimates agree quite closely from late winter to midsummer. However, the hydrologic model estimates less evapotranspiration in the fall, and more in midwinter, than the atmospheric budget.

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 a few kilometers upstream of the Zarqa-Jordan confluence to regulate its input mostly for the benefit of agricultural activities in the Jordan Valley. 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. Utilizing the BASINS-HSPF modeling environment, scenarios representing climate conditions with ±20% change in rainfall, and 1 • C, 2 • C and 3.5 • C increases in average temperature were simulated and assessed. The HSPF model was calibrated for the ZRW 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. Assessment based on daily records show much more modest r value of 0.785. The study shows that climate warming can dramatically impact runoffs and groundwater recharge in

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A Water Management Support System for Amman Zarqa Basin in Jordan has been developed. The water management support system employs the Water Evaluation and Planning system (WEAP). The water resources and demands in the basin were modeled as a network of supply and demand nodes connected by links. The model was calibrated for the year 2005 data and then validated for the year 2006 data. Validation results showed good agreement between calculated and measured inflows to wastewater treatment plants in the basin. The model was run for the year 2005 data as well as for four scenarios for the year 2025 which are Business As Usual (BAU) scenario, Advanced Wastewater Treatment (AWWT) scenario, the Red Sea, Dead Sea Channel (RSDSC) scenario and the optimistic scenario. The BAU scenario assumes that water use trends for the year 2025 follows predictable trends, the implementation of the disi project and the Wehda dam are main components of the BAU scenario. The AWWT scenario assumes that the effluent of As Samra wastewater treatment plant is treated to a level where it can be used for unrestricted irrigation within the basin and in the highlands. The main component of the RSDSC scenario is the implementation of the RSDSC project. The optimistic scenario combines both the AWWT scenario and the RSDSC scenario. The AWWT scenario, the RSDSC scenario, and the optimistic scenario are child scenarios of the BAU scenario. The results showed that neither domestic demand nor agricultural demand is met for the year 2005. The results also showed that A. Al-Omari et al. domestic and industrial demands can be satisfied for all the considered scenarios by proper management of the available resources. However, agricultural demand can't be satisfied for the business as usual scenario.

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