Sri Lanka’s agriculture is increasingly affected by rising temperatures and erratic rainfall, threatening paddy productivity and farmer livelihoods. This study assessed Alternate Wetting and Drying (AWD) as a drought-responsive water management practice through integrated climate modeling, APSIM simulations, and economic analysis. Results showed AWD enhanced water-use efficiency, reduced irrigation demand and methane emissions, and increased profitability, with NPV exceeding LKR 114,000 ha⁻¹. The findings confirm AWD as a financially and environmentally sound Climate-Smart Agriculture (CSA) intervention to strengthen drought resilience and sustainable water use.
Background
Rice is the staple food for nearly half of the global population and a key livelihood source for millions in developing countries (Li et al., 2024; Chen et al., 2017). Cultivated on over 155 million hectares, it contributes up to 59% of daily caloric intake for nearly 3 billion people across Asia (Pandey et al., 2010; Meng et al., 2005). Global demand is projected to rise by 25% by 2030 (Poutanen et al., 2022; IRRI, 2019). In low- and middle-income nations, rice occupies about one-fifth of total harvested area, underscoring its economic and social importance (Dawe et al., 2010).Climate change poses a major threat to rice systems through rising temperatures, erratic rainfall, and recurrent droughts that undermine yields and livelihoods (IPCC, 2007). Drought intensity and timing critically influence yield loss (O’Toole., 2004), while floods affect nearly 15 million hectares in Asia (Bates et al., 2008). Increasing salinity in coastal and deltaic regions further aggravates production risks (Dasgupta et al., 2015). These interlinked challenges demand adaptive land and water management strategies that consider both hydrological and socio-economic factors. CSA offers a holistic framework to enhance resilience and resource efficiency through three pillars—productivity, adaptation, and mitigation (Walsh et al., 2024; Mohapatra et al., 2025). It integrates improved crop varieties, water-saving irrigation, and climate-risk management suited to local contexts (CIAT, 2014). Among CSA practices, AWD has gained prominence as a sustainable alternative to continuous flooding, reducing irrigation water use by 25–37%, lowering methane emissions, and maintaining or improving yields by 10–20%. Despite these advantages, AWD adoption in Sri Lanka remains limited due to knowledge gaps, socio-economic constraints, and weak institutional support. Overcoming these barriers requires quantitative tools to assess agronomic and economic outcomes under varying climatic and management conditions. The Agricultural Production Systems Simulator (APSIM) provides an effective platform for analyzing crop–soil–climate interactions across scenarios (Keating et al., 2003; Holzworth et al., 2014). The APSIM-Oryza module, calibrated for local rice varieties and validated across major agro-climatic zones, reliably simulates yield, water use, and management responses (Amarasingha et al., 2014). However, most studies emphasize yield responses while neglecting economic viability, an essential factor influencing farmer adoption and policy relevance. To bridge this gap, the present study integrates climate projections, APSIM-based yield modeling, and cost–benefit analysis to assess the agronomic and economic impacts of AWD across Sri Lanka’s diverse agro-ecological regions. The findings aim to inform evidence-based policies for drought-responsive, resource-efficient, and economically sustainable water management.
Photo by Maitri Sheth
Actions taken
Research on climate impacts on rice using APSIM is limited, particularly for near-future, year-by-year climate variability, as most studies rely on long-term projections unsuitable for farm-level decision-making. To address this gap, the study focused on the 2026–2030 period to generate actionable insights on short-term climate impacts on rice production in Sri Lanka. Under the supervision of Prof. Jeevika Weerahewa, with guidance from co-supervisors Dr. Sumali Dissanayake and Dr. Nuwan De Silva, I defined the main objective as to evaluate AWD as a drought-responsive land and water management intervention by integrating APSIM-based biophysical simulation with economic analysis. This was refined into three specific objectives: (i) analyze current and future yields under business-as-usual conditions, (ii) assess yields under AWD, and (iii) evaluate associated costs and benefits. A key decision during planning was selecting the near-future temporal horizon for climate impact assessment, recognizing that farm-level decisions require timely, region-specific information. Historical daily weather data (1993–2023) for rainfall and temperature were compiled and analyzed using a time-series forecasting approach capable of capturing trends, seasonality, and variability. The resulting projections were downscaled to daily values compatible with APSIM, incorporating essential weather inputs, soil characteristics, crop phenology, and management practices. This methodological choice ensured accurate simulations of crop responses to anticipated climatic variability and provided a framework for integrating agronomic and economic analyses. The selection of study regions was guided by the need to represent Sri Lanka’s diverse rice-growing environments. The Dry Zone was subdivided into low-, moderate-, and high-yielding sub-regions based on historical yield patterns, while the Intermediate and Wet Zones were represented by low, mid, and up-country regions to capture spatial variability. The rice variety Bg-359 was selected due to its widespread cultivation and adaptability to multiple agro-climatic conditions. Among CSA interventions, AWD was prioritized for its ability to reduce water use, stabilize yields, and mitigate greenhouse gas emissions. Alternative strategies, including optimized fertilizer application, System of Rice Intensification (SRI), and Direct-Seeded Rice (DSR), were reviewed but not prioritized due to practical constraints and limited compatibility with existing irrigation systems. The selection process relied on literature review, expert consultations, and consideration of regional adoption feasibility. Economic feasibility was evaluated using cost-benefit analysis (CBA) based on actual field-level data, including labor, machinery, fertilizer, and material costs reported by farmers, rather than standard recommendations. Multiple scenarios were assessed: yields with and without climate change, and with and without AWD, over the periods 2020–2030 and 2025–2030. This allowed assessment of both climatic and management impacts on profitability, resource efficiency, and water use. Stakeholders, including local farmers, extension officers, and agricultural experts, were consulted to validate assumptions, data inputs, and management practices, ensuring real-world relevance and applicability. The integration of near-future climate projections, APSIM-based crop simulation, and economic analysis enabled a comprehensive assessment of agronomic and financial outcomes. By prioritizing representative regions, validated crop models, real-world management practices, and stakeholder-informed CSA interventions, the study ensured both scientific rigor and practical relevance. The approach provides actionable insights for policymakers, extension services, and farmers, promoting AWD adoption as a drought-responsive, resource-efficient, and economically sustainable strategy for paddy cultivation under near-future climate variability.
Outcomes
The results from APSIM simulations, climate forecasting, and cost-benefit analysis provide a comprehensive understanding of challenges, implementation issues, and potential pathways for sustainable, climate-resilient rice cultivation in Sri Lanka. Despite agronomic and economic benefits, systemic, technical, and institutional barriers limit widespread AWD adoption. AWD, as a drought-responsive water management intervention, produced notable agronomic, environmental, and economic outcomes across Dry and Intermediate Zones. Combining ARIMA-based climate projections with APSIM enabled precise evaluation of AWD’s capacity to enhance productivity and profitability under current and projected climates. AWD was excluded from poorly drained or waterlogged areas where intermittent wetting and drying is ineffective, limiting applicability to regions with suitable soils and water availability. Simulations for 2026–2030 showed regionally differentiated yield responses: without CSA interventions, Intermediate Zone and Dry zone moderate(DL2) yielding region could gain 4–29% due to moderate rainfall and temperatures enhancing soil moisture and photosynthesis, while Dry Zone low(DL1) and high-yielding(DL3) areas could decline up to 21% due to elevated temperatures and erratic rainfall increasing water stress and reducing soil fertility. AWD improved yields across most regions, mitigating negative climate effects, though high-yielding areas with advanced irrigation may require complementary CSA measures, including nutrient management and stress-tolerant varieties. Economic performance also improved; in Intermediate zone low country, CBA for 2020–2030 shows NPV rising from LKR 80,806 to LKR 114,421 per hectare per year, confirming robust returns. AWD reduces irrigation costs, optimizes water use, maintains soil aeration, enhances nutrient uptake, and lowers methane emissions, contributing to yield stability. Spatial yield differences reflect soils, irrigation, and rainfall, highlighting the need for region-specific management. AWD adoption faces persistent challenges: effective implementation requires soil moisture monitoring, technical knowledge, and field management capacity, often limited among smallholders; weak institutional coordination, limited awareness, lack of tools, resistance to change, liquidity shortages, and restricted credit access hinder investment despite proven profitability. Dry Zone districts such as DL3, one of the most productive rice belts, may face >21% yield declines under business-as-usual by 2030, with infrastructure deficiencies amplifying climate vulnerability. Extension services remain input-focused, and minor irrigation cannot consistently deliver wet-dry cycles, limiting adoption. Policy implications include integrating AWD into national CSA strategies, the National Adaptation Plan, and irrigation frameworks, supported by incentives for tools and credit, and strengthened simulation-based decision-making capacity. Primary beneficiaries are smallholders, gaining resilience, lower water costs, and improved profitability; secondary beneficiaries include communities via groundwater sustainability and reduced methane emissions. Sustainability depends on ongoing technical guidance, extension, financial incentives, and infrastructure improvement, with low implementation costs favoring economic viability and environmental benefits through water savings, aquifer recharge, and greenhouse gas mitigation. Overall, the project achieved objectives: improving water-use efficiency, stabilizing or enhancing yields, and increasing profitability. AWD demonstrates a technically feasible, economically viable, and environmentally sustainable pathway for climate-resilient rice production, with scaling and replicability contingent on addressing institutional, infrastructural, and behavioral constraints via adaptive, region-specific CSA strategies.
Lessons Learned
Effective AWD adoption requires comprehensive farmer training on its agronomic, economic, and environmental benefits, reinforced by government policies offering technical support, targeted extension services, and financial incentives, ensuring a smooth and sustained transition to climate-resilient rice cultivation while maximizing productivity and resource efficiency.
Collaborative partnerships among government agencies, NGOs and private sector actors enhance resource sharing, capacity building, and knowledge transfer, promoting technology dissemination, supporting replicability, and enabling effective scaling of CSA interventions across multiple regions, thereby fostering resilience, sustainability, and inclusive development in rice-based farming systems.
Robust monitoring and evaluation frameworks are vital to assess CSA impacts on yields, profitability, water efficiency, and environmental outcomes, facilitating adaptive management, iterative learning, and evidence-based scaling, thereby ensuring continuous improvement of practices, enhancing decision-making, and supporting resilient and sustainable rice production systems.
