Development of Rice Paddy Scheme Based on Noah Land Surface Model

Rice is a major food for 1/3 of the world's population (Khush, 1997). Unlike other crops, rice grows in shallow water layers for most of its growth period, and this rice cultivation area is called rice paddy. More than 90% of rice paddies are distributed in Asia, especially in East Asia and Southeast Asia (FAO, 2020). Therefore, modeling studies on the interaction between agricultural land and the lower atmosphere in these areas require a land model that takes into account the characteristics of the rice paddy. In this study, we developed a rice paddy scheme based on the Noah Land Surface Model (Noah LSM). The developed model was evaluated using the surface sensible, latent, and ground heat fluxes (H, LH, and G), and ground temperature (Tg) observed in three different rice paddies (Maruyama, 2021). The developed model uses a single layer canopy model to calculate the canopy heat/moisture transfer processes. It is designed to add a single layer of water over the soil layer during the irrigation period, at which time the water temperature is calculated based on the energy balance of the water layer. The results of the Noah LSM are set as a control simulation (NOAH-IRRI) in which the first and second layer of soil moisture are assigned as field capacity during the irrigation period. The developed model and control simulations were performed at 1-hour intervals for a period of about 100 days (including irrigation and non-irrigation periods) at each of the three observation sites. The average RMSEs of H, LH, G and Tg of NOAH-IRRI are 46 W m-2, 46 W m-2, 36 W m-2, 2.7 ℃, and IOA are 0.67, 0.97, 0.88, and 0.91, respectively. The average RMSEs of H, LH, G, and Tg of the developed model are 25 W m-2, 40 W m-2, 25 W m-2, and 1.6 ℃, and the average IOA are 0.78, 0.98, 0.96, and 0.97, respectively. The structure of the developed model and the contribution of the water layer to surface fluxes partitioning were also discussed.