A physically based hydrological model for paddy agriculture dominated hilly watersheds in tropical region

The hydrological response of tropical or sub tropical hilly agricultural watersheds is controlled by many critical factors such as topography, soil, vegetation, climate, rainfall characteristics, and local land use practices. The effect of these factors is highly interdependent and nonlinear in nature. In most of the hilly watersheds in south-east Asia rainfed paddy agriculture is the most dominating land use pattern. Therefore, both hillslopes and typical hydrological regimes of paddy fields significantly influence the hydrological behavior of these watersheds. However, non-availability of detailed hydro-meteorological data for these watersheds often limits the use of distributed hydrological models. The present study aims at developing a distributed hydrological model at watershed scale with limited hydro-meteorological data. The model describes the physical equations of vegetated hillslopes and paddy fields with other critical hydrological processes of the watershed. The model has been used successfully to simulate the hydrological behavior in two tropical paddy agriculture dominated watersheds (PADW) of the region. The model predicted the peak flow and seasonal runoff coefficients for both the watersheds using daily rainfall data from limited number of raingauge stations. A model sensitivity analysis has shown that average retention depth and degree of soil impermeability in paddy fields are the most influencing parameters.