Different configurations of the Weather and Research Forecasting (WRF-ARW) regional climate model, centered over the Eastern Nile Basin, have been investigated. Extensive sensitivity analyses were carried out to test the model performance in simulating precipitation and surface air temperature, focusing on the horizontal extent of the simulation domain, the mesh size and the parameterizations of the boundary layer, radiation, cloud microphysics, and convection. A simulation period of 2 years (1998–1999) was used to assess the model performance during the rainy season (June–September) and the dry season (December–March). Three sets of numerical experiments were conducted. The first tested the effects of changing the horizontal extent of the simulation domain; three domains have been examined to investigate, e.g., the effect of including a larger part of the Indian Ocean, for which no significant impact was found. The second set of experiments tested the sensitivity of WRF to the horizontal mesh size (about 16, 12, and 10 km). It was found that increased resolution results in a more accurate simulation of precipitation and surface temperature. The third set of experiments was designed to select the optimal combination of physics parameterizations. All simulations were forced by ERA-Interim reanalysis data to provide initial and boundary conditions, including sea surface temperature, and the Noah land surface model (NPAH) was used to simulate land surface processes. To rate the model performance, we used a range of statistical metrics, summarized with a scoring technique to obtain a single index that ranks different alternatives. The simulated precipitation was found to be much more sensitive to the choice of physics parameterization compared to the surface air temperature. Precipitation was most sensitive to changing the cumulus and the planetary boundary layer schemes, and least sensitive to changing the microphysics scheme. Modifying the long-wave radiation scheme led to more significant changes compared to the short-wave radiation scheme
The study of water balance is considered here as a way to assess the performance of regional climate models and examine model uncertainty and as an approach to understanding regional hydrology, especially interactions between atmospheric and hydrological processes. We studied the atmospheric and terrestrial water balance over the Eastern Nile Basin (ENB) region using the weather research and forecasting (WRF) model. The model performance in simulating precipitation and surface air temperature is assessed by comparing the model output with the data from the Global Precipitation Climatology Center dataset for precipitation and from the University of Delaware for temperature. The results show that the simulated and observed values correlate well. In terms of water balance, the study region was found to be a sink for moisture, where the atmospheric convergence is negative during most of the time. Most of the precipitation originates from moisture fluxes from outside the domain, and the contribution of local evapotranspiration to precipitation is limited, with small values for the moisture recycling ratios year-round. The atmospheric moisture content does not show significant monthly or annual variation. The results indicate that the terrestrial water storage varies seasonally, with negative fluxes during most of the year, except June, July, and August, when most of the precipitation occurs.
The present work tried to estimate the runoff discharge and groundwater recharge volumes for the catchments of Ras Gharib area using the Soil Conservation Service curve number (SCS-curve number) and the water balance methods. The two methods were selected among other methods used by hydrologists due to simplicity and popularity for application in arid and semi-arid areas like Egypt. The watershed delineation and streamlines for Ras Gharib region have been accomplished using ArcMap 10 GIS and the 1-arc second DEM which demonstrated three basins in the study area. The rainfall data points nearby the study area, extracted from the TRMM data, have been used as input for the Log-Pearson III distribution in order to calculate the design storm for different return periods (100, 50, 25, and 10 years). The results of applying the SCS model estimated the runoff depths as 19.86, 8.00, 2.32, and 0.06 mm for the different return periods, respectively. The total surface runoff volumes reached the study area are 34.78, 14.02, 4.07, and 0.11 Mm 3 , respectively for the selected return periods, whereas the total groundwater recharge volumes for the selected storm return periods are 58.16, 31.34, 18.14, 3.18 Mm 3 , respectively.
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