Distributed hydrologic modeling in a partially urbanized agricultural watershed using water and energy transfer process model

The water and energy transfer process (WEP) model, which has been successfully applied to urbanized watersheds, is improved for hydrologic modeling in an agricultural watershed by developing a paddy model. The new model is used to simulate the Yata watershed at 100 m grid size and variable time step. A 4 year 3 month simulation is performed for model calibration and verification. Model results are compared to measured values of river discharges, groundwater levels, and soil moisture contents. Sensitivity of annual water budgets and hourly river discharges to rainfall estimation error is also analyzed. The verified model is applied to simulate the long-term variation of water budgets and flood-retarding effects of paddy fields in the watershed. Study results indicate that: (1) the WEP model is applicable to agricultural watersheds in addition to urbanized ones; (2) annual weather variations give more obvious impact on water budgets than urbanization in the agricultural watershed; and (3) paddy fields play important roles both in reducing flood peaks and in conserving low river flow in the watershed.