Development of a mesh-based distributed runoff model incorporated with tank models of several land utilizations in a Southeast Asian watershed

We propose a new long-term rainfall-runoff model for a Southeast Asian watershed. To reflect the impact of land use changes associated with rural development, and the nonuniformity of rainfall in tropical regions, a mesh-based distributed runoff model was constructed. Four tank models (paddy, upland field, urban, and forest) were incorporated into each mesh element, to capture the outflow from different land uses. Each mesh element was connected to the river network to reproduce the rainfall-runoff flow processes. By incorporating a watershed groundwater tank, we improved the representation of the baseflow component which is important in long-term runoff analysis. To shorten the calculation time and improve the application to other watersheds, we introduced an inflow/outflow matrix that defines the direction of rainwater flow between adjacent mesh elements. The model was applied to the Dau Tieng watershed in Southern Vietnam, with an area of 2,700 km². The model was run for the period 1999-2009, and the calculated discharge was compared with the observed values, and a good model fit was achieved. As the model represents the flow processes from rainfall to river discharge with highly versatile tank models, it can be applied to watersheds where hydrological data for model verification are scarce, which is a common issue for many developing countries in Southeast Asia.