Reconstruction of Historical Atmospheric Data for Mekong River Basin by a Hydroclimate Model

In order to perform water balance studies over the Mekong river basin a historical atmospheric data set is needed over the basin at fine time and spatial grid resolutions as input to the watershed-scale water balance models of the basin. Due to various reasons in this region, such historical atmospheric data over this region are not available at the desired fine time-space scales. Consequently, it is necessary to utilize a regional coupled atmospheric-hydrologic modeling technology in order to downscale the available historical global atmospheric databases that are at very coarse resolution (~ 285km), to the Mekong river basin region at fine spatial resolution (~ 20km). U.S. National Center for Atmospheric Research (NCAR) and U.S. National Center for Environmental Prediction (NCEP) have historical atmospheric data for the 1956–2006 period over the whole world at 2.5° latitude x 2.5° longitude spatial grid resolution and at 6-hr time increments. However, over the Mekong basin, the 2.5° resolution corresponds approximately to 285 km. At such spatial resolution it is impossible to obtain the necessary spatial detail for the historical atmospheric conditions. Therefore, a regional, fully-coupled atmospheric-hydrologic hydroclimate model of Mekong basin, called "RegHCM-Mekong" was developed at 20 km spatial grid resolution in order to accommodate the complex topographical and land surface features of this basin. RegHCM-Mekong was then used to downscale the coarse time-space resolution NCEP-NCAR historical atmospheric data to produce 1-hour-increment meteorological information on rainfall, air temperature, specific humidity, wind velocity, solar radiation and net radiation at 0.2 degrees spatial resolution (about 20 km) over the whole Mekong basin during a historical period. The comparisons of RegHCM-Mekong reconstructed historical rainfall fields in time and space against point-location observations and against the spatial maps of historical precipitation observations yielded satisfactory results.