Extended Abstract

the river system in the basin. The magnitude of the catchment area is usually variablefrom 10 2 to 10 3 km 2 . At present, the lumped models are dominative in hydrologicalservice.As a new approach of hydrological modeling developed with development of DigitalEarth, the distributed modeling describes the hydrologic processes at small scale andthen adding these up and routing the flows through the landscape by taking an explicitaccount of spatial variability of processes, input, boundary conditions, land use andwathershed characteristics provided by Digital Elevation Models (DEM). The scale ofmodel grid can vary from 10 1 m x 10 1 m up to 10 3 m x 10 3 m with the catchment areaand the purpose of modeling. Considering the limitation of DEM and the computingspeed, the solution of 1km x 1km ~ 4km x 4km is usually adopted in the real-timeoperational use.Model resolution has been at the center of a debate in the hydrologic communityabout the advantages/disadvantages of lumped versus distributed models (Figure 2,Smith et al., 2004a.). One side of the debate notes that lumped models create coarsebut accurate results, even though they do not effectively represent spatial variability ofhydrologic processes, or intra-basin differences in elevation or terrain. Distributedmodels are designed to work at spatial and temporal scales finer than lumped models.The other side of the debate, the argument in favor of distributed models, posits thatbecause distributed models can account for differences in site specific characteristics,including basin size, topography, land cover. It has not been popularly used inhydrological service yet because the precipitation inputs (QPE/QPF) do not meet theneeds of spatial and temporal resolution of hydrologic models.Fig. 2 Differences between lumped and distributed model approaches3. Catchment hydrological forecastingCatchment hydrological forecasting is one of main tasks in hydrological servicesystem. Its functions include providing short-term flood forecasting and long-term-155-