Coupled Regional Hydroclimate Model and Its Application to the Tigris-Euphrates Basin

Abstract

To establish a basinwide water management plan for the Tigris-Euphrates (TE) watershed, it is necessary to perform rigorous water balance studies of the whole watershed—at least for critical historical drought and flood conditions and under various water resources development scenarios. Water-balance studies over the watershed require climatic and hydrologic data sets, corresponding to historical critical flood and drought periods, at fine time and spatial grid resolutions provide the necessary hydroclimatic information. The Regional Hydroclimate Model of the Tigris-Euphrates (RegHCM-TE) and the associated geographic information system (GIS) were developed to downscale large-scale atmospheric data sets over the TE watershed and to reconstruct the aforementioned climatic and land hydrologic data sets at fine spatial and time increments. In RegHCM-TE, the earth system over the TE watershed is modeled as a fully coupled system of atmospheric processes aloft coupled with the atmospheric boundary layer, land-surface processes, surface and subsurface hydrologic processes, and the interactions among the various hydrologic and atmospheric processes. The parameters of the model are estimated by using existing global and local GIS data. By using the large-scale global historical atmospheric databases as its initial and boundary conditions, RegHCM-TE has been used to reconstruct historical hydroclimate data at a grid size of 15 km over the TE watershed, for which only very sparse hydrologic observations were available. RegHCM-TE and its model validation are described in this paper.