Mitigating Greenhouse Gas Emissions from Rice Production in the Philippines: A System Dynamics Approach

Greenhouse gases (GHG) emissions from agricultural production, most especially from methane (CH₄) and nitrous oxide (N₂O) emissions from rice paddies and from excessive use of fertilizers, contribute significantly to global warming. This paper presents a system dynamics (SD) model to forecast agricultural GHG emissions and rice production in the Philippines over a fourteen year time horizon (2026 to 2040) under four different scenarios. These scenarios are: a) the conventional method of irrigation used by farmers today, b) Alternate Wetting and Drying (AWD) of puddles created during flooded rice cultivation, applied in combination with biochar amendments (AWD & biochar), c) Urea Deep Placement (UDP) which is a precise placement of nitrogen containing fertilizers, and d) mechanization of animal powered tillage (mechanization). The model was validated against independent benchmarks for agricultural emissions with Mean Absolute Percentage Errors (MAPE) ranging from 0.96% to 1.52%. The results obtained from the different scenarios showed that Scenario 2 (AWD & biochar) resulted in the largest average emissions reduction of 25% (range: 23%–27%) and highest average rice yields of 6.81% (range: 5%–8%) over the entire 14-year period compared to the baseline. Scenario 3 (UDP) yielded average emissions reduction of 4.5% (range: 4%–5%) and average increase in rice yields of 5.42% (range: 4%–6%). The fourth scenario or mechanization of animal powered tillage yielded minimal average emissions reduction of 0.2% (range: 0.2%–0.3%) and average increase in rice yields of 0.04% (range: 0%–0.1%). These percent changes in emissions and yield reported in the paper are averages over the entire 14-year period and are computed on an annual basis by comparing each year in the four scenarios with corresponding years in the baseline scenario. Results indicate that two approaches namely AWD with biochar and UDP whether singly or in combination are most feasible near-term options to develop climate smart agriculture or climate smart rice production in the country and are within the country’s Nationally Determined Contributions (NDCs) under the Paris Agreement.