Contents & Foreword, Characterizing And ... - IRRI books

Description of the study areaWe completed an extensive descriptive analysis of the Mekong River Delta usingavailable survey, secondary-source, and GIS data. In this review, we considered characteristicssuch as the following biophysical variables: location and accessibility ofrice producers and markets, soils, rainfall and temperatures, and the seasonal floodingsituation and problem of saltwater intrusion on farmland. We relied on GIS datacompiled by IRRI and its collaborators for most of this analysis. We also examinedsurvey and secondary price data to consider changes in agricultural policies, real pricesof rice inputs and outputs, and market development in the Mekong River Delta in the1990s, and to characterize the demographic characteristics and resource endowmentsof surveyed farms. Extensive work had previously been carried out using the surveydata to describe the evolution of rice agriculture, and in particular the evolution ofcosts and revenues accruing to rice farmers in the region during the 1990s (IAS 1997,1998). Here we report only the small portion of this work that relates directly to theGIS techniques explained earlier. Table 1 reports selected descriptive statistics fromthe data set used in the study.Figure 3 superimposes land use reported by farms in the eight surveyed villageson a land-use map for the Mekong Delta (circa 1996). The figure helps to highlightthe benefits of integrating GIS with farm survey data. The base map provides a completecharacterization of land use, while information from the farm-level survey addsa time dimension and provides detailed data on farm resources and activities. Thefigure shows the high level of correspondence between land use captured from remotesensing presented on the map and that reported by farms completing the longitudinalsurvey.We generated rainfall indicators for each of the villages from which householdswere selected for the longitudinal survey using weekly rainfall data from 24 weatherstations in the Mekong River Delta. In this initial analysis, we worked with aggregateannual rainfall as a measure of fresh water available to nonirrigated rice plots. Theamount of rainfall is important not only as a water source for rainfed crops, but alsobecause of its influence on flood levels and saltwater intrusion in the dry season.Across the Delta, rainfall is heaviest in the far southwest coast of the peninsula andtends to decline as one goes from the Ca Mau area to the northeast (toward Ho ChiMinh City). The highest total annual rainfall in 1996 (a heavy rainfall year) was about3,100 mm, whereas the lowest rainfall reported that year was about 1,650 mm. Weused linear spatial interpolation to generate rainfall measures for the eight localitieswhere the survey was conducted. The technique takes the weighted average of reportedrainfall at all the weather stations surrounding the surveyed villages, with theweight assigned to each weather station being inversely proportional to the distancebetween the station and the selected village.Our description of the study area included an accessibility analysis of the eightsurveyed villages in the Delta. Figure 4 shows the main transportation routes in thearea. The principal routes used by the farms interviewed for the longitudinal surveyare shown in green (surface-water routes) and black (road and ferry routes). Theaccessibility indicators calculated for the surveyed farms in the Mekong River DeltaIntegration of biophysical and socioeconomic constraints . . . 451