Akihiko Kotera

Agro-ecological interpretation of rice cropping systems in flood-prone areas using MODIS imagery

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 multicropping 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 Waveletbased 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 winterspring 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

A modeling approach for assessing rice cropping cycle affected by flooding, salinity intrusion, and monsoon rains in the Mekong Delta, Vietnam

We developed a crop scheduling model for rice cultivation in the Vietnam Mekong Delta (VMD), focusing on the adaptive behavior of crop planning to various water resource constraints. In addition, we also examined the effects of environmental change on rice cultivation in the last decade. In the VMD, multiple rice cropping is practiced under a variety of adverse water conditions, including flooding, salinity intrusion, and irregular monsoon rains. These environmental changes influence the durations of growing seasons and the number of crops per year, resulting in changes in productivity. To validate the performance of the model, we compared model estimates for the heading date and changes in leaf area index at nine sites with estimates of these parameters derived from MODIS satellite time series data for the period 2002–2006. The root mean square errors of heading date between the modeled and satellite data in the upper, middle, and coastal regions of the delta were 17.6, 11.2, and 13.0 days, respectively. Based on the model, we examined case studies to assess the changes in cropping cycles and crop failures in the VMD due to extreme flooding in 2000 and salinity intrusion in 2004 by applying evaluation indices defined by available period for cultivation (APC) and safe margin for cropping (SMC) which is defined as the marginal time between APC and the period required for cultivation. Findings of case studies suggested that a small difference in the SMC of the cropping pattern is critical to the stability and productive capacity of the rice crop.

Modeling complex flow dynamics of fluvial floods exacerbated by sea level rise in the Ganges-Brahmaputra-Meghna Delta

Global warming is likely to exacerbate future fluvial floods in the worlds mega-delta regions due to both changing climate and rising sea levels. However, the effects of sea level rise (SLR) on fluvial floods in such regions have not been taken into account in current global assessments of future flood risk, due to the difficulties in modeling channel bifurcation and the backwater effect. We used a state-of-the-art global river routing model to demonstrate how these complexities contribute to future flood hazard associated with changing climate and SLR in the worlds largest mega-delta region, the Ganges-Brahmaputra-Meghna Delta. The model demonstrated that flood water in the main channels flows into tributaries through bifurcation channels, which resulted in an increase in inundation depth in deltaic regions. We found that there were large areas that experienced an increase in inundation depth and period not directly from the SLR itself but from the backwater effect of SLR, and the effect propagated upstream to locations far from the river mouth. Projections under future climate scenarios as well as SLR indicated that exposure to fluvial floods will increase in the last part of the 21st century, and both SLR and channel bifurcation make meaningful contributions.

Classification of crop fields in northeast Thailand based on hydrological characteristics detected by L-band SAR backscatter data

Synthetic aperture radar (SAR) backscatter amplitude image data have proven useful in estimating soil moisture levels and in approximating areas of water inundation over large regions. Based on the pattern of seasonal change in the backscatter coefficient at each image pixel, this study classified a variety of crop fields in Northeast Thailand according to their hydrological characteristics. L-band horizontal-transmit horizontal-receive (HH) polarization images from advanced land observing satellite phased array type L-band synthetic aperture radar (ALOS-PALSAR) at six dates from January to December over the rainy season (May to November) in 2007 were used. Fifteen clusters of pixels were generated using the k-means method, with five variables obtained by taking the difference between the backscatter coefficient for the dry season (January) and the other five dates, effectively removing effects of soil surface roughness. As a result, a detailed spatial distribution of hydrological characteristics that accurately reflected topographical features and hydrological conditions was obtained.