Improvements in the Land and Crop Modeling Over Flooded Rice Fields by Incorporating the Shallow Paddy Water

Abstract

Flooded rice paddies are important for modifying land surface energy and water budgets, especially in Asian countries. This study incorporated shallow paddy water into the Noah with Multi-Parameterization (Noah-MP) model to enhance its performance in capturing the distinct features of small Bowen ratios over flooded rice fields. The paddy surface water was parameterized as one integrated layer along with the top soil layer, and meteorological measurements from two crop sites in Japan, that is, SAITO (early rice) and SAGA (late rice), were employed for model evaluation at the field scale. The simulation results show that the model performance was significantly improved by combining the incorporation of paddy water and the calibration of rice crop parameters, particularly at SAGA. Compared with the reference run using the original version of Noah-MP for SAGA, the underestimation in latent heat and the overestimation in sensible heat during daytime were decreased by ∼74 W m⁻² (∼67%) and ∼92 W m⁻² (∼55%), respectively. Approximately 60%–70% of this improvement was contributed by using calibrated rice crop parameters, while the rest of 30%–40% was from further incorporating paddy water. The decreased ground surface resistance owing to the presence of paddy water was crucial for capturing the features of small Bowen ratios. The observed water depth might help mitigate the underestimation of latent heat nonlinearly. This work may benefit the study of land-atmosphere interactions and local and regional weather and climate in Asia with the widely used coupled Weather Research and Forecasting/Noah-MP model.