Comparison between SWAT and SWAT+ for simulating streamflow in a paddy-field-dominated basin, northeast Thailand

Kasetsart University, Department of Irrigation Engineering, Nakhon Pathom, 73140, Thailand

^* Corresponding author: ekasit.k@ku.th

Abstract

The performance of the well-known Soil and Water Assessment Tool (SWAT) and the new SWAT+ for streamflow simulation in a paddy- field-dominated basin was compared. The Lam Sioa River Basin, northeast Thailand (drainage area of 3,394 km²) was selected. The data inputs consisted of DEM, land use, soil, and climate (rainfall, temperature, sunshine hour, wind speed and humidity). The model parameters used the default values from SWAT database and daily simulation was conducted from 2005 to 2017. The division of sub-basins into “landscape units” is one of new features of SWAT+. The total number of HRUs defined from SWAT+ were higher than those from SWAT because the sub-basins derived from SWAT+ contained two landscape units (floodplain and upslope). With the default model parameters, the model performance indicators were found below the satisfactory rating. Both models simulated relatively high streamflow at the beginning of rainy season, while the observed streamflow was still not occurred. In paddy field, rainfall excess become ponding water, not surface runoff. The appropriate representation of paddy field in SWAT model should be further investigated.