Adaptive irrigation management by Balinese farmers reduces greenhouse gas emissions and increases rice yields

Abstract

The potential for changes in water management regimes to reduce greenhouse gases (GHG) in rice paddies has recently become a major topic of research in Asia, with implications for top-down versus bottom-up management strategies. Flooded rice paddies are a major source of anthropogenic GHG emissions and are responsible for approximately 11% of global anthropogenic methane (CH 4 ) emissions. However, rice is also the most important food crop for people in low- and lower-middle-income countries. While CH 4 emissions can be reduced by lessening the time the plants are submerged, this can trigger increased emissions of nitrous oxide (N 2 O), a more potent GHG. Mitigation options for CH 4 and N 2 O are different, and minimizing one gas may increase the emission of the other. Accurate measurement of these gas emissions in rice paddies is difficult, and the results are controversial. We analysed these trade-offs using continuous high-precision measurements in a closed chamber in 2018–2020. Based on the results, we tested a bottom-up adaptive irrigation regime that improves nitrogen uptake by rice plants while reducing combined GHG emissions and nitrogen runoff from paddies to reefs in agricultural drainages. In 2023, we undertook a follow-up study in which farmers obtained higher rice yields with adaptive intermittent irrigation compared to uniformly flooded fields. These results use the polycentric, self-governing capacity of Balinese subaks for continuous adaptation. This article is part of the theme issue ‘Climate change adaptation needs a science of culture’.

Climate change adaptation needs a science of culture

“…Examples include agricultural techniques, migration, and even climate-related policy and funding. Because their livelihoods are entwined with climate, farmers are often at the forefront of climate change mitigation and adaptation, creating innovations that can reduce greenhouse gas emissions [ 14 ] or selectively adopting suggestions from organizations, policymakers and researchers based on what works locally [ 15 ]. Humans past and present have often used migration to respond to climate-related risks—although, thanks to borders and other restrictions, climate-related migration can be difficult today.…”

“…[ 41 – 43 ]). Several articles in this theme issue provide detailed qualitative and quantitative data on the relationship between cultural practices and contemporary climate, which can be compared and contrasted across contexts [ 16 , 44 – 46 ] and can be compared to environmental data, such as carbon emissions data [ 14 ]. Agent-based models draw from both past and contemporary data to simulate future outcomes (e.g.…”

“…For example, consider rice paddies or swidden systems, also known as slash-and-burn, milpa , or shifting cultivation. Adjacent paddies and swiddens may become spatially correlated approximating a power law: a candidate adaptation adopted by one farmer impacts their neighbours in an exponentially decreasing, nonlinear way, such that close neighbours are more impacted than those further away [ 14 ]. This can signal a transition from exclusively local control to a complex adaptive system, which can approach Pareto optimality—where no one in the system could do better without negatively impacting someone else's outcomes [ 82 ].…”

“…Importantly, all three levels—micro, meso and macro—are interconnected and often overlapping. For example, the adoption of variants by individual farmers at the micro level (like different approaches to watering) affects ecology at the meso level [ 98 ] and determines which adaptations become locally predominant [ 14 , 15 ]. In other cases, national-level policies (macro) impact the transmission of TEK (micro), with implications for its preservation among Indigenous peoples (meso; [ 44 , 46 ]).…”

Climate change adaptation and the back of the invisible hand

“…The question of which kinds of structural interventions are both politically feasible and environmentally effective is the subject of an enormous amount of current research, including many of the papers in this issue [58][59][60][61][62]. It is well beyond the scope of our discussion to assess the relative strengths and weaknesses of these policy proposals.…”