Estimating seasonal basin rainfall using Tabu search

Basin areal rainfall is often estimated utilizing gauge data observed at specific locations adjusted on the basis of prescribed weighting factors for each station. The resultant data have many hydrological and meteorological applications. Several hydrometeorological factors, such as spatial rainfall variability, orographic effects, and synoptic frontal systems can greatly affect gauge-catch efficiency in watersheds that lack sufficient gauge densities. As a result, gauge weightings that are determined by conventional approaches (e.g., arithmetic averages, and the Thiessen polygon) that lack consideration for watershed and rainfall characteristics may introduce unexpected errors in estimated basin rainfall. Our approach is to combine hydrological routings and Tabu search using errors of estimated stream discharges as the objective function to determine gauge-weighting factors. Through hydrological routings, basin and rainfall characteristics are implicitly considered into the estimation of discharges representing an integrated basin response to rainfall forcing. The Lanyang River Basin located in northeastern Taiwan is the domain of interest, where wet- and dry-season rainfalls are mainly attributed to typhoons and the winter monsoon, respectively. Wet-season results show significant orographic effect on gauge weightings due to the large cyclonic circulation interacting with the mountainous topography. Dry-season results further demonstrate the importance of orographic effect, especially at one particular station located on the windward side of the mountains with respect to the persistent frontal system of the winter monsoon.