Unravelling the Impact of Changing Rainy Seasons on Rice Production in Southeast Asia: A Climate Change High-resolution Perspective

Southeast Asia is a major contributor to global rice production. Yet, this production is increasingly threatened by climate change, particularly by changes in the rainy season. In this study, We examine the impact of shifts in seasonal cumulative rainfall and characteristics of the rainy season on rice production across Southeast Asia. To achieve this, we utilize the framework of the High-Resolution Model Intercomparison Project (HighResMIP) in conjunction with rice production estimates from the World Food Studies (WOFOST) crop model. Our findings reveal a trend towards drier conditions during the dry season across the region. A decrease in cumulative rainfall is observed during December-January-February in mainland Southeast Asia and the Philippines, with rainfall reductions reaching up to 33\% and 15\% in certain areas, respectively. In Indonesia, a decrease in rainfall during the June-July-August period was observed across the majority of the region, with some areas experiencing a decrease of up to 48\%. This trend is also accompanied by delays in the onset of the rainy season and a reduction in its duration across most of the region. A significant reduction in the rainy season duration, up to 27 days, was found over the southern Philippines, where delays in the onset of the season are followed by an early cessation. The changes in rainfall patterns negatively impact rainfed rice production. Increased rainfall during the second growing season (GS-2) in certain areas of Mainland Southeast Asia and the Philippines enhances rice yields, while reduced rainfall during GS-1 and GS-3 in Java reduces yields. The most substantial effects are observed during GS-3 in Java, with a substantial decrease in yield attributed to reduced rainfall and a shorter rainy season. In addition, rice irrigation simulations indicate that rising temperatures will shorten the growing season, consequently resulting in lower yields. Effective adaptation strategies are crucial to mitigate the decline in rice production. Our analysis suggests that a simple adaptation measure, such as shifting from the C3 photosynthesis type to the C4 photosynthesis crop, may not suffice. Additionally, enhancing and refining agricultural systems is needed to bridge potential yield gaps, emerging as a recommended approach.