Quoted from: https://www.atm.helsinki.fi/peex/images/modellingplatform/Model_CH4MOD.pdf 

CH4MOD was developed to predict methane fluxes from rice paddy soils. The model associated this process with rice growth, organic C depletion and environmental factors (Huang et al., 1998; 2004). The model’s input parameters included the rice grain yield, the soil sand percentage, the amount of organic amendment, the water management pattern, and the daily air temperature. The outputs are the daily and annual rates of CH4 production and emissions. The model was validated against a total of 94 field observations that covered the main rice cultivation regions from northern (Beijing, 40º30'N, 116º25'E) to southern (Guangzhou, 23º08'N, 113º20'E) China and from eastern (Hangzhou, 30º19'N, 120º12'E) to southwestern (Tuzu, 29º40'N, 103º50'E) China. This model can reasonably simulate CH4 flux from irrigated rice fields (Huang et al., 2004).

Below is quoted from: Xie, Baohua, Zaixing Zhou, Xunhua Zheng, Wen Zhang, and Jianguo Zhu. "Modeling methane emissions from paddy rice fields under elevated atmospheric carbon dioxide conditions." Advances in Atmospheric Sciences 27, no. 1 (2010): 100-114. https://link.springer.com/article/10.1007/s00376-009-8178-4 

Based upon the understanding of the processes of CH4 production, oxidation and emission, Huang et al. (1998) have developed a semi-empirical model to predict CH4 emissions from paddy rice fields. This model simulates CH4 emissions with a minimal number of inputs and parameters (following the Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories of the IPCC, 2000). Taking account of the water regime effects on CH4 production and transportation via bubble ebullition, Huang et al. (2004) then modified the original model and named the improved version CH4MOD (hereafter referred to as CH4MOD 1.0). Tested with 94 cases, CH4MOD 1.0 can provide statistically satisfactory estimates of CH4 emissions frompaddy rice fields that are continuously flooded or remain non-waterlogged but wet with moist irrigation (Huang et al., 2004). However, it can not simulate CH4 emissions from paddy rice fields with multiple mid-season drainage episodes (i.e., intermittent irrigation) very well. Further improvement of CH4MOD 1.0 is required in order to provide better estimates of water regime effects on CH4 emissions.