Identifying Alternative Wetting and Drying (AWD) Adoption in the Vietnamese Mekong River Delta: A Change Detection Approach

Abstract

Alternative wetting and drying (AWD) is an increasingly popular water-saving practice in rice production in the Vietnamese Mekong River Delta, especially considering the impact of projected climate change and reduced water availability. Unfortunately, it is very difficult to determine adoption without deploying thousands of costly household surveys. This research used European Space Agency Sentinel-1a and 1b radar data, combined with in-situ moisture readings, to determine AWD adoption through change detection of a time series wetness index (WI). By using a beta coefficient of the radar data, the WI avoided the pitfalls of cloud cover, surface roughness, and vegetative interference that arise from the sigma coefficient data. The analysis illustrated an AWD adoption likelihood scale across the delta and it showed potential for the use of remotely sensed data to detect adoption. Trends across the Vietnamese delta showed higher adoption rates inland, with lower adoption of AWD in the coastal provinces. These results were supported by a simultaneous effort to collect household level adoption data as part of the same project. However, correlation between the WI values and in situ soil moisture meter readings were most accurate in alluvial soils, illustrating a particularly strong relationship between soil type and WI model robustness. The research suggests that future change detection efforts should focus on retrieving a multi-season dataset and employing a power density analysis on the time series data to fully understand the periodicity of dry down patterns.

Global benefits of non‐continuous flooding to reduce greenhouse gases and irrigation water use without rice yield penalty

“…Additional research will help reduce the uncertainty of the assessments. Future investigation of current adoption extent and degree of non‐continuous flooding practices through interdisciplinary endeavors from household survey, in‐situ filed monitoring as well as innovative remoting sensing technologies would be high priority to realize actual mitigation potentials assessments of IRR and GWP (Filipe et al, 2018; Lovell, 2019). Long‐term experiments should be designed and conducted to evaluate the long‐term and comprehensive climate effects of practicing non‐continuous flooding and explore sustainable integrated managements (e.g.…”

Climate Change Mitigation: Policies and Lessons for Asia

“…One appeal of AWD as a mitigation strategy is that the ability to remotely monitor the practice is quickly improving. Radar measurements from the European Space Agency's Sentinel-1 sensors have shown promise for mapping AWD in Viet Nam (Lovell 2019;Phan et al 2021). Integrating these methods into verification protocols will likely require more research-for instance, inundation status gets harder to detect toward the end of the season when crops are fuller in size (Phan et al 2021) and yet these stages may be important for determining net GHG impact.…”

Trans-Disciplinary Responses to Climate Change: Lessons from Rice-Based Systems in Asia

“…In the Philippines,~80,000 farmers have adopted AWD on~90,000 ha (~6% of total irrigated rice area). In Vietnam, on the other hand, there has been large-scale adoption of AWD in major rice production provinces in the Mekong River Delta-Dong Thap and An Giang-according to a recent study based on satellite data, household surveys, and in situ moisture readings [69].…”