These women and men negotiate a Portable Family identity, based onactions rather than interactions, and oscillating between the urban-productive home and the rural-reproductive home.Alternate Wetting and Drying is an irrigation technique in which water is applied to the field a number of days after the disappearance of ponded water. This is in contrast to the conventional irrigation practice of continuous flooding in which farmers never let ponded water disappear. AWD allows intermittent drying during certain stages of rice growth because roots of the rice plant are still adequately supplied with water due to the initial flooding. The number of days in which the field is allowed to be “non-flooded” before irrigation is applied can vary from one day to more than 10 days. Under the effects of climate change, water scarcity will be a main concern for Asian rice producers in the dry season. Regionally, applying AWD could conserve fresh water resources and either extend the growing cycle during the dry season or expand rice production areas. Unfortunately, estimating adoption of AWD is quite difficult. Determining the extent and degree of AWD adoption has proven difficult. The Irrigated Rice Research Consortium introduced AWD to paddy fields in the Mekong River Delta beginning in 1997 through the various projects in coastal provinces, such as Bac Lieu, as well as inland provinces, such as An Giang . There have been a number of evaluations of barriers to adoption , plant grow table and one widely accepted estimate of 40,000 farmers adopting the practice by 2011 .
However, these studies are based on small sample sizes, expert interviews, and household surveys. These methods can be time consuming, expensive, and prone to subjectivity. Thus, the core objective of the project is to determine if remotely sensed data can be used to determine the geographic extent and the degree of adoption in MRD Provinces in Vietnam. Radar remote sensing is an effective data for mapping soil moisture regardless of cloud cover or atmospheric interference . Synthetic Aperture Radar detects a back scatter digital number using microwave bursts from satellites that orbit earth. Radar data has fewer limitations than pure reflectance data due to the lack of cloud cover interference . Sentinel-1 in particular shows promise for change-detection approaches to understanding surface wetness . There are three transformations possible with Sentinel-1 data: alpha , beta , and nought . We do not discuss ϒ° transformation possibilities in this paper. Further, σ° poses a great deal of trouble in creating a reliable wetness index. Vegetative interference must be carefully calculated and accounted for as a function of σ° . Surface roughness is also a confounding factor in σ° transformation and use . However, SAR σ° data has been used to understand different characteristics of the rice paddy and plant, including the contribution of leaf area index, and plant growth stage and type . Ithas also been used successfully to understand the extent of the triple rice crop . Most recently, a number of authors have used the β° transformation of the SAR data in a change detection analysis. Experts have used change detection to create wetness indices that avoid the pitfalls of cloud cover interference inherent in reflectance data .
The change detection approach also reduces complications of surface roughness and vegetative interference that arise from the alpha transformation. For these reasons, the GIS team adopted the β° transformation and change detection approach for the purposes of this project, referred to as a “multi-temporal SAR for SWC change detection” that uses multiple passes from the same incidence angle and polarization . The chapter proceeds in the following fashion. The first part of the chapter discusses the environmental setting of the Mekong River delta. It then outlines the need for developing low-cost methods for determining adoption of AWD and a promising remote sensing approach using change detection of a wetness index. The third part of the chapter outlines the results of the work flow we explored. We conclude with the implications of these results, the limitations of the study, and some promising avenues for further validation of this method.Sustainable water management is a regionally urgent issue in Vietnamese agriculture. Vietnam has a complex system of barrages, weirs, and dikes to mitigate flood and salt water intrusion . The canal system expanded from two canals in 1824, 40 canals in 1934, to hundreds in the 1980s . Today, the channel network is over 50,000 kilometers long. Community groups in the delta often govern sluice gates and this control over hydrology allows for a double- or triple-cropping system. However, since the canal system was built, Vietnam has experienced subsequent water quality issues, salt-water intrusion, and canal bank erosion.
In maximum flooding conditions, these flow obstructions can worsen flood impacts, preventing saline waters from escaping croplands. Dredging canals, upgrading roads, and other waterway improvements to protect crops can cause between five and 10 additional days of flooding, or between 0.2 and 0.3 additional meters of water depth during peak flood conditions . Additionally, planned dam construction upstream in Laos could also have a synergistically negative effect with projected climate change impacts . Sediment deposits would accumulate behind the dam, causing a deficit of sediment and nutrient deposition downstream in the latter half of the century when projected impacts of climate change will be worse than the first half of the century. This may, in turn, have impacts on rice and other crop production. Flooding is a strength and weakness of the Mekong River Delta agricultural setting. The area is considered a monsoon system, with the rainy season lasting between May and October and averaging between 1400 and 2400 millimeters annually, and the length of the growing season is between 270 and 300 days A large proportion of the Malay Peninsula is seasonally inundated, which includes much of the Mekong River Delta in Vietnam. The floodwaters are filled with nutrient-rich sediment, which replenishes agricultural land and reduces the need for agricultural inputs . However, climate change is expected to increase the average and maximum water levels and flood duration in the Mekong River Delta between 2010 and 2049 . This will negative consequences for annual crops, infrastructure integrity, floodplain vegetation, and most likely decrease the amount of fertile land. The changes in flooding may increase ecosystem productivity and produce dry season water availability, which could allow extended cropping. Drought is one of the most formidable vulnerabilities in rice cropping systems of Vietnam, in spite of the vast irrigation network. Because rice yield is linearly related to the number of days it is grown in saturated soil, water shortages can have a severe impact on rice production . Lack of water reduces biomass, grain set, and forestalls emergence. It also disrupts crop management techniques such as weeding, fertilization, and transplanting. It is especially damaging during flowering and can incur a large weed problem if drought occurs during emergence periods. In locations without a clay hardpan, acidic water can infiltrate from deeper soil during the dry season or drought years . However, some authors have taken a nutrient management approach to the drought issue,arguing that drought is less important than how loss of soil-water saturation impacts uptake of nitrogen, phosphorus, and iron, as well as impacting toxic levels of aluminum . Additionally, small undulations in rice fields and between bunded fields, known as toposequences, can produce equally important hydrologic shifts as precipitation patterns. Climate change precipitation changes may cause yield fluctuations in already irrigated lands due to anticipated lack of irrigation water. This presents a hurdle for increasing yields in the light of increased water insecurity. Vietnam has a double- or triple-cropping system in the project area, hydroponic table which is sometimes subject to salt-water intrusion from the South China Sea and Gulf of Thailand. HISTORY OF AWD AWD was developed through the research efforts of the International Rice Research Institute , one of the major research centers under the CGIAR.
In particular, the Water-Savings Workgroup under the Irrigated Rice Research Consortium was instrumental in the development and dissemination of this technology in the major rice-growing countries of Asia. The IRRC was established in 1997 with the aim of providing a platform to facilitate the identification, development, dissemination, and adoption of natural resource management technologies suitable for irrigated rice-based ecosystems in several Asian countries, including Vietnam. With funding support mainly from the Swiss Agency for Development and Cooperation through four project phases , the IRRC has provided a mechanism that has expedited partnerships between national agricultural research and extension system partners and scientists from IRRI. In Vietnam, AWD has been introduced to paddy fields in the MRD through the various projects of IRRI, CGIAR, the Climate Change Agriculture and Food Security project, and Climate and Clean Air Coalition . There are projects in coastal provinces, such as Bac Lieu, as well as inland provinces, such as An Giang. With respect to specific IRRI/IRRC dissemination efforts for AWD, there has been an integrated approach to promoting AWD. This integrated approach has been built on the long established relationship between IRRI/IRRC and the Plant Protection Department of the Ministry of Agriculture and Rural Development . Through the IRRI-PPD partnership, AWD was first evaluated in An Giang Province in 2005-2006 for three successive rice-growing seasons. In 2006, AWD was incorporated into a large-scale existing program called “Three Reductions, Three Gains” that aimed to reduce inputs of fertilizers, pesticides, and seeds. In 2009, technologies that reduce irrigation water use and post-harvest losses were included and the program was transformed into the “One Must Do, Five Reductions” program. The successful evaluation and dissemination of AWD in Vietnam through the 3R3G program and subsequently the 1M5R program were facilitated by the widespread media campaigns and training on AWD through these integrated programs. The collaboration of IRRC with the PPD was instrumental in this endeavor. Moreover, 1M5R is now a national policy that aims to make rice production more sustainable. All the components of the IM5R program are being promoted and wide-scale implementation is being done throughout An Giang and in nearby provinces in the Mekong Delta. Promotion of this program is also underway for the northern part of Vietnam, particularly in the Red River Delta. The AWD technique starkly contrasts to traditional rice cultivation. Rice fields are not kept continuously submerged, but are allowed to dry intermittently during the rice growing stage. The number of days in which the field is allowed to be “non-flooded” before irrigation is applied can vary from 1 day to more than 10 days . The underlying premise behind this irrigation technique is that the roots of the rice plant are still adequately supplied with water for some period even if there is currently no observable ponded water in the field. To assist farmers in the practical implementation of AWD, a simple tool was introduced. The field water tube can be made of plastic pipe or bamboo or any cheap material, and is embedded in the paddy field to a depth of 15 cm, with the soil removed from inside the tube, to reveal the perched water-table level. During AWD implementation, the field is irrigated to a depth of around 5 cm whenever the ponded water level has dropped to about 15 cm below the surface.The best source of data for this project currently includes the European Space Agency’s Sentinel-1 satellite. The Vietnamese Mekong River Delta is approximately 40,000 square kilometers, with the majority of the area covered by a single tile of ascending and descending passes by Sentinel 1-a and 1-b. SAR data is downloadable in raster format, with thousands of individual cells representing a setarea in space, or tile. Each cell within the tile of Sentinel-1 data represents 10 by 10 meters for which a back scatter number, or digital number , is given for that area of space. Each cell contains two bands of data collected from the satellite platform at different sending and retrieving angles: vertically sent and vertically retrieved , and vertically sent and horizontally retrieved . The VV band was used in this analysis because it has a higher accuracy in other similar wetness index studies . Table 1 outlines acquisition dates for which VV and VH data was available for our study location.