Agro-ecological Interpretation of Rice Cropping Systems in Flood-prone Areas using MODIS Imagery

<p><i>This study attempts a new approach using Moderate Resolution Imaging Spectroradiometer (MODIS) time-series imagery to evaluate the agro-ecological interpretation of rice-cropping systems in flood-prone areas. A series of wavelet-based methodologies were applied to reveal the dynamic relationships among annual flood inundation, rice phenology, and land-use change in the Vietnamese Mekong Delta (VMD). The rice-heading dates of multi-cropping areas were estimated by detecting the local maximal points in smoothed Enhanced Vegetation Index (EVI) profiles, using the Wavelet-based Filter for determining Crop Phenology (WFCP) and Wavelet-based Filter for evaluating the spatial distribution of Cropping Systems (WFCS) methods. The temporal information for annual flood intensity was determined for the six annual flood seasons over the period from 2000 to 2005 by the Wavelet-based Filter for detecting spatio-temporal changes in the Flood Inundation (WFFI) method. Analysis using remote sensing techniques revealed an interaction between the regional environment and agricultural activity in the VMD. First, comparing the estimated heading date of the winter-spring rice with the end date of flood inundation showed that the cropping season for the winter-spring rice in the flood-prone area fluctuates depending on the annual change in flood scale. This result implied that the onset of winter-spring rice is spatially and temporally linked to the variable flood-recession season, and hence the annual change in flood scale. Secondly, the field survey study of the yearly change in the rice-cropping system in the An Giang province from 2000 to 2006 showed that the triple rice-cropped area in the An Giang province expanded from 2000 to 2005, because the construction of a ring-dyke system and water-resource infrastructure allowed an additional rice crop to be sustained during the flood season. However, the area of the third rice crop in the An Giang province decreased drastically in 2006 as a result of the management of pest outbreaks. Although the regional water-resource environment was gradually transformed by the construction of water-resource infrastructure, in order to achieve favorable conditions for a third rice crop during the flood season, the rapid change in land-use for agricultural activity may complicate the spatio-temporal configuration of the agricultural environment in the VMD. This case study used MODIS time-series imagery to help understand the functions of the macro-scale ecosystem, including annual flood regimes and human activity.</i></p>