Southeast Asia must narrow down the yield gap to continue to be a major rice bowl

Southeast Asia produces 26% of global rice and 40% of exports and is critical to global food security. Despite historic gains from the Green Revolution via increased cropping intensity and yield, recent challenges—stable or declining harvested area, limited scope for irrigation expansion, and yield stagnation in several countries—raise concerns about sustaining a regional rice surplus as demand grows with population. The study asks whether Southeast Asia can maintain its role as a major rice supplier by increasing yields on existing cropland. Using a data-intensive modelling approach, it estimates current yield gaps (difference between potential and farmer yields), identifies where and when they are largest, and assesses future self-sufficiency and export potential under alternative yield-improvement scenarios to 2040.

Background work has documented sustained growth in rice yields through the Green Revolution, followed by stagnation in several Southeast Asian countries. Prior global and regional analyses predicted relatively stable per capita rice demand, implying total demand growth from population increases. Earlier yield-gap studies in specific countries or seasons reported sizable gaps and highlighted management and environmental constraints. Research on rice yield potential suggests limited recent gains for inbred varieties, modest adoption and constraints of hybrid rice in Southeast Asia, and the need for agronomic improvements and loss reductions. Previous top-down models often overlook spatial and seasonal diversity; this study extends the literature with region-wide, spatially explicit, system-specific yield-gap mapping and scenario analysis.

The study focused on six major Southeast Asian rice producers (Cambodia, Indonesia, Myanmar, Philippines, Thailand, Vietnam), covering ~97% of regional production and emphasizing irrigated and rainfed lowland systems (~98% of production). Using Global Yield Gap Atlas protocols, researchers delineated representative climate zones and selected reference weather station (RWS) buffers (69 irrigated; 61 rainfed) to cover at least 50% of national harvested area per water regime, informed by SPAM 2010 maps and local expert input. Long-term daily weather data (measured or NASA-POWER for gaps) underwent quality control. Soil properties were specified for rainfed simulations (texture, depth, water table); irrigated simulations assumed no soil limitations. Crop management calendars and dominant varieties per system and season were compiled via structured questionnaires. Yield potential (irrigated) and water-limited yield potential (rainfed) were simulated with ORYZA v3, using representative modern varieties (e.g., Inpari 32, OM1490, PSBRc80, PSBRc10; KDML105 for Thai aromatic rainfed rice with adjusted parameters). For rainfed systems, groundwater depth scenarios (shallow, medium, deep) captured water limitation uncertainty, with sensitivity analyses on soil texture and groundwater depth. Yield gaps were computed as the difference between simulated potential (or water-limited potential) and average farmer yield, weighted by area across cropping sequences and seasons; annual gaps accounted for cropping intensity. Current (2019–2020) demand was derived from national production, trade, and stock changes. Future (2040) demand used UN population projections and per capita demand changes from three econometric models (IRRI Global Rice Model, IMPACT, RECC), with regional totals including five additional Southeast Asian countries (Brunei, Laos, Malaysia, Singapore, Timor-Leste). Scenario assessment assumed constant harvested area and irrigation share, and evaluated three yield trajectories to 2040: S1 (continuation of recent trends), S2 (full closure of exploitable gap to 80% of potential for irrigated, 70% for rainfed), and S3 (half closure of exploitable gap). Rice self-sufficiency ratio (SSR) and surplus were computed as production-to-demand ratio and difference, respectively.

- Yield potential and gaps: Regional average yield potential was 8.9 Mg ha⁻¹ per crop (range 5.5–10.2). Dry-season potential was ~10% higher than wet season. For Thai rainfed aromatic rice, water-limited potential averaged 5.3 Mg ha⁻¹ per crop. The average yield gap across Southeast Asia equaled 48% of potential, with irrigated gaps averaging 42% and rainfed 55%. Due to higher cropping intensity, annual yield gaps were larger in irrigated systems (7.5 Mg ha⁻¹ yr⁻¹) than rainfed (5.2 Mg ha⁻¹ yr⁻¹). - Country differences: Irrigated yield gaps were smaller in Indonesia and Vietnam (37–39%) than in Cambodia, Myanmar, Philippines and Thailand (51–60%). For rainfed rice, Indonesia’s gap was ~49% versus 54–66% in the other countries. Subnationally, Vietnam’s Red River Delta had a larger gap than the Mekong Delta (46% vs 39%). Seasonal patterns varied, with 7–16% larger gaps in the dry vs wet season for irrigated rice in Indonesia and the Philippines, but the opposite in Cambodia and Vietnam. - Baseline self-sufficiency: Regional SSR (2019–2020) was 1.10 with a 17 Mt surplus; Thailand and Vietnam were net exporters, while Indonesia and the Philippines relied on imports. - Scenario outcomes by 2040: • S1 (current trends): Regional SSR declines to 1.03, nearly eliminating surplus; Indonesia and the Philippines remain non-self-sufficient. • S2 (full exploitable-gap closure): SSR reaches 1.55 with ~100 Mt surplus; all six countries achieve self-sufficiency. Required annual yield gains: ~79–135 kg ha⁻¹ yr⁻¹. • S3 (half exploitable-gap closure): SSR rises to 1.29 with ~54 Mt surplus; Indonesia becomes self-sufficient and Philippine imports are greatly reduced. Required annual yield gains: ~36–67 kg ha⁻¹ yr⁻¹ (largest in Myanmar, smallest in Thailand).

Findings indicate that without accelerated yield growth, Southeast Asia’s capacity to supply regional needs and export surplus rice will erode, threatening regional and global food security. Spatially explicit yield-gap mapping shows substantial, actionable room to raise yields, especially in Cambodia, Myanmar, the Philippines and Thailand, and highlights where irrigated systems offer the greatest annual production gains due to higher cropping intensity. Scenario analysis demonstrates that narrowing exploitable gaps—particularly achieving even half-closure—would maintain or expand regional surpluses and help import-dependent countries approach self-sufficiency. While the study does not model climate change impacts explicitly, it argues that their near-term (to 2040) effect is small relative to current gaps and can be mitigated by adaptation. The results support targeted investments in agronomy, inputs, extension, and enabling policies to accelerate yield gains, stabilize markets, and sustain Southeast Asia’s pivotal role in the global rice supply.

The study quantifies where and by how much rice yields in Southeast Asia can increase on existing cropland and shows that narrowing current exploitable yield gaps is essential to sustain regional self-sufficiency and export capacity by 2040. Even half-closing these gaps could nearly triple the regional surplus relative to today. Strategic, system- and season-specific interventions—such as improved nutrient and water management, integrated pest management, risk reduction tools for rainfed systems (e.g., pumps, insurance), and better access to technologies and markets—are needed. Additional opportunities include reducing harvest and post-harvest losses and improving milling rates. Future research should refine subnational targeting of interventions, integrate climate-change adaptation pathways, assess environmental footprints of intensification, and evaluate socio-economic barriers to adoption, alongside continued breeding and management innovations.

- Climate change effects on yields and management were not explicitly modeled; impacts to 2040 were assumed relatively small, introducing uncertainty. - Genetic improvements in yield potential over time were not considered; adoption constraints of hybrid rice were noted. - Analysis excluded upland and deep-water rice (≈3% of production) and assumed constant harvested area, irrigation share, and production in five additional Southeast Asian countries. - Rainfed simulations faced uncertainties in groundwater depth and soil variability; default or adjusted soil parameters were used where detailed data were lacking. - Some weather inputs relied on gridded NASA-POWER data for stations without measurements. - The spatial sampling covered ≥50% of harvested area per water regime via RWS buffers, requiring upscaling assumptions. - Demand projections depend on econometric model outputs and milling rate conversions, adding model-related uncertainty.