Abstract:
Haors are large bowl-shaped flood plain depressions located mostly in north-eastern part of Bangladesh covering a total area of over 19,998 square kilometers and very susceptible to flash flood. These haor basins are being used for fish production in monsoon and boro rice production in dry season. However, they often experience severe damage to boro rice in the pre-monsoon months of April and May due to flash flood’s sudden high discharges and velocities, and unexpected rise and recession. Therefore, an attempt was made for the year of 2007 to 2014 with a view to mapping flash flood inundation using remote sensing and Geographic Information System (GIS) data and assessig the impact of the flash flood on total boro rice production in Taherpur Upazila of northeastern Bangladesh.
This study revealed the extent of the inundation occurred by flash flood in the Taherpur upazila from 2007 to 2014 and how they affected the boro rice production. The Moderate Resolution Imaging Spectroradiometer (MODIS) TERRA and AQUA satellite data were used for mapping flash flood inundation using two different methods viz. density slicing of near-infrared band and density slicing of Normalized Difference Vegetation Index (NDVI). Using the 30 ground truthing points, SRTM 30m DEM data, and field data, threshold values of the water pixel digital number of cloud free near-infrared band and NDVI image were identified to map flash flood. On the other hand, flash flood timing was found out by observing the water level of the Jadukata River. Satellite image processing, analysis and density slicing operation were carried out with MODIS Reprojection Tool, QGIS, and ILWIS.
The accuracy of the inundation mapping was assessed with confusion matrix. The accuracy of inundation mapping using near-infrared band and NDVI image was 92.50% and 87.50%, respectively. Inundation mapping technique with higher accuracywas used for assessing the impact of flash flood on boro rice production.
Flash flood timing was plotted against the boro rice production to find out the relationship between flash flood timing and boro rice production. Relationships between production of different types of boro rice and flash flood timing were also derived. It was found that the extent of inundation has weak correlation with the boro rice production. Studies using high temporal and spatial resolution satellite image may lead to better result.
From semi-structured interview with farmers, it was observed that the impact of flash flood heavily relies on the duration of inundation, hailstorm, and some other factors. In addition, introduction of new rice varieties, cultivation of flood-tolerant rice varieties, availability of chemical fertilizer and local measures of rice harvesting were the reasons for rice production improvement.
