VELAS: A fully-distributed daily hydrologic feedback model with emphasis on vegetation, land cover, and soil water dynamics

We present a daily hydrologic feedback model, VELAS (the VEgetation-LAnd cover-Soil water dynamics), to simulate daily responses of hydrologic processes including interception, runoff, evapotranspiration, infiltration, and recharge under various conditions of vegetation, land cover, and soil in a fully-distributed manner. The daily soil water balance is a key element to link surface and subsurface models as it calculates infiltration and groundwater recharge by considering a time delay routing through a vadose zone down to the groundwater table. MODFLOW is adopted to simulate groundwater flow and interaction with surface water components as well. The model can be localized by simple modification of soil and crop properties. The application of VELAS to a watershed in the Geum River Basin in Korea shows different daily responses of hydrologic feedbacks for different types of land cover in the same watershed. The comparison between the estimated runoff from VELAS and the observed runoff data shows a good correlation with the coefficient of 0.81. The calculated groundwater elevation and the observed groundwater elevation also show a good correlation with the coefficient of 0.98 and the percent error less than 1.8%. The exteneded application to the entire Geum River Basin for the climate change and land cover transition during the period from 2011 to 2050 shows the capability of VELAS to predict long-term hydrologic feedbacks. The results of land cover change prediction by the Land Change Modeler show a strong agreement between the actual land cover and the predicted land cover. The predicted responses of hydrologic feedbacks reflect the impacts of the climate and land cover change.