Muhammad Al-Amin Hoque

Assessing tropical cyclone impacts using object-based moderate spatial resolution image analysis: a case study in Bangladesh

ABSTRACT The environmental and societal impacts of tropical cyclones could be reduced using a range of management initiatives. Remote sensing can be a cost effective, accurate, and potential tool for mapping the multiple impacts caused by tropical cyclones using high-to-moderate spatial resolution (5–30 m) satellite imagery to provide data on the following essential parameters – evacuation, relief, and management of natural resources. This study developed and evaluated an approach for assessing the impacts of tropical cyclones through object-based image analysis and moderate spatial resolution imagery. Pre- and post-cyclone maps of artificial and natural features are required for assessing the overall impacts in the landscape that could be acquired by mapping specific land cover types. We used the object-based approach to map land-cover types in pre- and post-cyclone Satellite Pour l’Observation de la Terre (SPOT) 5 image data and the post-classification comparison technique to identify changes in the particular features in the landscape. Cyclone Sidr (2007) was used to test the applicability of this approach in Sarankhola Upazila in Bangladesh. The object-based approach provided accurate results for classifying features from pre- and post-cyclone satellite images with an overall accuracy of 95.43% and 93.27%, respectively. Mapped changes identified the extent, type, and form of cyclone induced impacts. Our results indicate that 63.15% of the study area was significantly affected by cyclone Sidr. The majority of mapped damage was found in vegetation, cropped lands, settlements, and infrastructure. The damage results were verified through the high spatial resolution satellite imagery, reports and pictures that were taken after the cyclone. The methods developed may be used in future to assess the multiple impacts caused by tropical cyclones in Bangladesh and other similar environments for the purposes of tropical cyclone disaster management.

Modelling tropical cyclone risks for present and future climate change scenarios using geospatial techniques

ABSTRACT Tropical cyclones and their devastating impacts are of great concern to coastal communities globally. An appropriate approach integrating climate change scenarios at local scales is essential for producing detailed risk models to support cyclone mitigation measures. This study developed a simple cyclone risk-modelling approach under present and future climate change scenarios using geospatial techniques at local scales, and tested using a case study in Sarankhola Upazila from coastal Bangladesh. Linear storm-surge models were developed up to 100-year return periods. A local sea level rise scenario of 0.34 m for the year 2050 was integrated with surge models to assess the climate change impact. The resultant storm-surge models were used in the risk-modelling procedures. The developed risk models successfully identified the spatial extent and levels of risk that match with actual extent and levels within an acceptable limit of deviation. The result showed that cyclone risk areas increased with the increase of return period. The study also revealed that climate change scenario intensified the cyclone risk area by 5–10% in every return period. The findings indicate this approach has the potential to model cyclone risk in other similar coastal environments for developing mitigation plans and strategies.

A new estimate of carbon for Bangladesh forest ecosystems with their spatial distribution and REDD+ implications

In tropical developing countries, reducing emissions from deforestation and forest degradation (REDD+) is becoming an important mechanism for conserving forests and protecting biodiversity. A key prerequisite for any successful REDD+ project, however, is obtaining baseline estimates of carbon in forest ecosystems. Using available published data, we provide here a new and more reliable estimate of carbon in Bangladesh forest ecosystems, along with their geo-spatial distribution. Our study reveals great variability in carbon density in different forests and higher carbon stock in the mangrove ecosystems, followed by in hill forests and in inland Sal (Shorea robusta) forests in the country. Due to its coverage, degraded nature, and diverse stakeholder engagement, the hill forests of Bangladesh can be used to obtain maximum REDD+ benefits. Further research on carbon and biodiversity in under-represented forest ecosystems using a commonly accepted protocol is essential for the establishment of successful REDD+ projects and for the protection of the country’s degraded forests and for addressing declining levels of biodiversity.

Modelling tropical cyclone hazards under climate change scenario using geospatial techniques

Tropical cyclones are a common and devastating natural disaster in many coastal areas of the world. As the intensity and frequency of cyclones will increase under the most likely future climate change scenarios, appropriate approaches at local scales (1-5 km) are essential for producing sufficiently detailed hazard models. These models are used to develop mitigation plans and strategies for reducing the impacts of cyclones. This study developed and tested a hazard modelling approach for cyclone impacts in Sarankhola upazila, a 151 km2 local government area in coastal Bangladesh. The study integrated remote sensing, spatial analysis and field data to model cyclone generated hazards under a climate change scenario at local scales covering < 1000 km2. A storm surge model integrating historical cyclone data and Digital Elevation Model (DEM) was used to generate the cyclone hazard maps for different cyclone return periods. Frequency analysis was carried out using historical cyclone data (1960 - 2015) to calculate the storm surge heights of 5, 10, 20, 50 and 100 year return periods of cyclones. Local sea level rise scenario of 0.34 m for the year 2050 was simulated with 20 and 50 years return periods. Our results showed that cyclone affected areas increased with the increase of return periods. Around 63% of study area was located in the moderate to very high hazard zones for 50 year return period, while it was 70% for 100 year return period. The climate change scenarios increased the cyclone impact area by 6-10 % in every return period. Our findings indicate this approach has potential to model the cyclone hazards for developing mitigation plans and strategies to reduce the future impacts of cyclones.