Flooded rice systems, be they irrigated, rainfed or deepwater rice, emit significant amounts of methane (CH4), contributing about 10–12% of anthropogenic emissions from the global agriculture sector. Alternate Wetting and Drying (AWD) involves the periodic drying and re-flooding of rice fields. About two weeks after transplanting, the field is left to dry out until the water level is at 15 cm below the soil surface. Then the field is flooded again to a water depth of approximately 3–5 cm before draining again. This irrigation scheme is repeated during the crop growth cycle, except during flowering time, when the field is maintained at a flooded water depth of 3–5 cm.
Relationship to CSA
When used correctly, AWD does not reduce productivity compared to continuous flooding, and may in fact increase yields by promoting more effective tilling and stronger root growth of rice plants. By reducing the number of irrigation events, AWD helps farmers avoid the risk of water scarcity and increases the reliability of downstream water supply, an attribute likely to become more important as populations increase and climates progressively change. AWD has a significant mitigation potential and is assumed to reduce methane (CH4) emissions by an average of 48% compared to continuous flooding (IPCC 2006). 2 Combining AWD with nitrogen-use efficiency and the management of rice straw can further reduce GHG emissions. However, more widespread field-based measurements are required to properly quantify these mitigation effects (Cooper et al. 2013). 3
Impacts and lessons learned 4
- About 40% of rice farmers in China practice some form of water-saving technology and short intervals of non-flooded conditions are common among rice farmers in northwestern India and in Japan (more than 80%). AWD-like practices have continued to spread in other countries such as North Vietnam (Castillo et al. 2012) 5.
- In some cases, 10–20% of the benefit gained by decreasing CH4 emission is offset by the increase in N2O emissions. However, net global warming potential (GWP) is still significantly lower under AWD than in continuously flooded fields.
- The mitigation potential of AWD depends strongly on its proper execution. Incomplete drainage (not allowing the water table to drop to 15 cm below soil surface) can result in negligible reductions in GHG emissions.
CCAFS Big Facts - Alternate wetting and drying for more efficient rice farms in Vietnam: https://ccafs.cgiar.org/bigfacts/#theme=evidence-of-success&subtheme=crops&casestudy=cropsCs3
Richards M, Sander BO. 2014. Alternate wetting and drying in irrigated rice. CSA Practice Brief. Copenhagen, Denmark: CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS).https://cgspace.cgiar.org/rest/bitstreams/34363/retrieve Alternate wetting and drying (AWD) is a rice management practice that reduces water use by up to 30% and can save farmers money on irrigation and pumping costs. AWD reduces methane emissions by 48% without reducing yield. Efficient nitrogen use and application of organic inputs to dry soil can further reduce emissions. Incentives for adoption of AWD are higher when farmers pay for pump irrigation.
IPCC. 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories Programme, Eggleston, H.S., Buendia, L., Miwa, K., Ngara, T. and Tanabe, K. (eds.) IGES, Japanhttp://www.ipcc-nggip.iges.or.jp/public/2006gl/
These 2006 IPCC Guidelines for National Greenhouse Gas Inventories build on the previous Revised 1996 IPCC Guidelines and the subsequent Good Practice reports in an evolutionary manner to ensure that moving from the previous guidelines to these new guidelines is as straightforward as possible. These new guidelines cover new sources and gases as well as updates to previously published methods where technical and scientific knowledge have improved. This guidance assists countries in compiling complete, national inventories of greenhouse gases. The guidance has been structured so that any country, regardless of experience or resources, should be able to produce reliable estimates of their emissions and removals of these gases. In particular, default values of the various parameters and emission factors required are supplied for all sectors, so that, at its simplest, a country needs only supply national activity data. The approach also allows countries with more information and resources to use more detailed country-specific methodologies while retaining compatibility, comparability and consistency between countries. The guidance also integrates and improves earlier guidance on good practice in inventory compilation so that the final estimates are neither over- nor under-estimates as far as can be judged and uncertainties are reduced as far as possible. Guidance is also provided to identify areas of the inventory whose improvement would most benefit the inventory overall. Hence limited resources can be focused on those areas most in need of improvement to produce the best practical inventory. The IPCC also manages the IPCC Emission Factor Database (EFDB). The EFDB was launched in 2002, and is regularly updated as a resource for inventory compilers to use to assist them by providing a repository of emission factors and other relevant parameters that may be suitable for use in more country-specific methodologies. The 2006 Guidelines are the latest step in the IPCC development of inventory guidelines for national estimates of greenhouse gases. In the opinion of the authors, they provide the best, widely applicable default methodologies and, as such, are suitable for global use in compiling national greenhouse gas inventories. They may also be of use in more narrowly-defined project based estimates, although here they should be used with caution to ensure they correctly include just the emissions and removals from within the system boundaries. We would also like to thank all the authors (over 250) as well as reviewers, review editors, the steering group and the TFB for their contributions and experience. We would also like to thank all the governments who contributed by hosting meetings (Oslo, Norway; Le Morne, Mauritius; Washington, USA; Arusha, Tanzania; Ottawa, Canada; Manila, The Philippines; Moscow, Russian Federation; and Sydney, Australia) as well as those who supported authors and other contributors. Finally we would like to express our gratitude to the NGGIP TSU and the IPCC Secretariat for their invaluable support throughout the entire process of drafting and producing these guidelines.
Cooper PJM, Cappiello S, Vermeulen SJ, Campbell BM, Zougmoré R, Kinyangi J. 2013. Large-scale implementation of adaptation and mitigation actions in agriculture. CCAFS Working Paper No. 50. Copenhagen, Denmark: CCAFS.https://cgspace.cgiar.org/rest/bitstreams/24708/retrieve This paper identifies sixteen cases of large-scale actions in the agriculture and forestry sectors that have adaptation and/or mitigation outcomes, and distils lessons from the cases. The cases cover policy and strategy development (including where climate-smart objectives were not the initial aim), climate risk management through insurance, weather information services and social protection, and agricultural initiatives that have a strong link to climate change adaptation and mitigation. Key lessons learned include: - Trade-offs can be avoided, at least in the near-term and over limited spatial scale - We need cost-effective and comparable indices for measuring GHG fluxes and for monitoring adaptive capacity - Strong government support is crucial to enable large-scale successes - Upfront costs may be substantial and can be met from multiple sources - An iterative and participatory learning approach with investment in capacity strengthening is critical.
Richards M, Sapkota T, Stirling C, Thierfelder C, Verhulst N, Friedrich T, Kienzle J. 2014. Conservation agriculture: Implementation guidance for policymakers and investors. Climate-Smart Agriculture Practice Brief. Copenhagen, Denmark: CCAFS.https://cgspace.cgiar.org/rest/bitstreams/34456/retrieve Conservation agriculture (CA) can increase resilience to climate change and has the potential to contribute to climate change mitigation. The benefits of CA are highly site- specific. Innovative approaches are needed to overcome barriers for uptake of CA by smallholders.
Castillo GE, Le MN, Pfeifer K. 2012. Oxfam America: Learning from the System of Rice Intensification in Northern Vietnam. Focus 19, Brief 15. Washington, DC: International Food Policy Research Institute (IFPRI).http://cdm15738.contentdm.oclc.org/utils/getfile/collection/p15738coll2/id/126992/filename/127203.pdf Despite Vietnam’s remarkable success in reducing poverty from almost 60 percent of the population in 1993 to 14 percent in 2008, 18 million Vietnamese still live on less than US$1.25 a day. Vietnam supplies a fifth of the rice consumed worldwide, and yet millions of rice farmers grow barely enough for subsistence. Over 9 million farmers in Vietnam own less than half a hectare of paddy land, generally fragmented into 6–10 smaller plots. Some 90 percent of these farmers live in the country’s northern region. They are highly vulnerable to external shocks, especially climate change and the high and volatile price of food and agricultural inputs. Meanwhile, extension services often overlook their needs and rely on prescriptive, top-down approaches that have failed to invest in their ongoing adaptive capacity.