Spatio-temporal analysis of agriculture in the Vietnamese Mekong Delta using MODIS imagery

New methodologies using MODIS time-series imagery were developed for revealing spatio-temporal changes of agricultural environments and land use patterns in the Vietnamese Mekong Delta. The following methodologies were proposed: a wavelet based filter for crop phenology (WFCP), a wavelet-based filter for evaluating the spatial distribution of cropping systems (WFCS), and a wavelet-based filter for detecting spatio-temporal changes in flood inundation (WFFI). The WFCP algorithm involves smoothing the temporal profile of the Enhanced Vegetation Index (EVI) using the wavelet transformation approach. As a result of validation using the agricultural statistical data in Japan, it was shown that the WFCP was able to estimate rice growing stages, including transplanting date, heading date and harvesting date from the smoothed EVI data, with 9-12 days accuracy (RMSE). The WFCS algorithm was developed for detecting rice-cropping patterns in the Vietnamese Mekong delta based on WFCP. It was revealed that the spatial distribution of rice cropping seasons was characterized by both annual flood inundation around the upper region in the rainy season and salinity intrusion around the coastal region in the dry season. The WFFI algorithm was developed for estimating start and end dates of flood inundation by using time-series Land Surface Water Index and EVI. Annual intensity of Mekong floods was evaluated from 2000 to 2004, at a regional scale. Applying a series of wavelet-based methodologies to the MODIS data acquired from 2000 to 2006, it was confirmed that the cropping season for the winter-spring rice in the flood-prone area fluctuated depending on the annual change of flood scale. It was also confirmed that the triple rice-cropped area in the An Giang province expanded from 2000 to 2005, because the construction of a ring-dike system and water-resource infrastructure made it possible to sustain a third rice cropping season during the flood season. The proposed methodologies (WFCP, WFCS, WFFI) based on MODIS time-series imagery made it clear that while the rice cropping in the Vietnamese Mekong Delta was quantitatively (annual flooding) and qualitatively (salinity intrusion) affected by water-resource changes, there were some regions where the cultivation system was changed from double rice cropping to triple rice cropping because of the implementation of measures against flooding.