Abstract

In Bangladesh, the mangrove ecosystem of the Sundarbans region is vital to both the environment and the economy. Natural disasters, especially cyclones, cause significant damage to mangrove vegetation. To assess the impact of the cyclone on the Sundarbans, a long-term dataset focused on cyclone is required. Mapping mangrove forests using satellite imagery is an effective technique to find crucial information for mangrove forest conservation and management. We used Google Earth Engine (GEE) and Landsat 5, 7, and 8 satellites to assess the mangrove vegetation changes due to the cyclone during the study period. In this study, we analyzed the two indexes, Enhanced Vegetation Index (EVI) and Normalized Difference Vegetation Index (NDVI) for immediate pre-cyclone and immediate post-cyclone time for 8 cyclones that happened over the Sundarbans mangrove forest between 1990- 2020. From the statistical analysis, we found that cyclone wind speed is significantly negatively correlated with a lower NDVI and EVI value at a 95% significant level (0.05 confidence level). Among 8 cyclones the most catastrophic damage happened during cyclone SIDR (2007), on this time NDVI value decreased from -0.41223 to -1.0, and wind speed was the highest among the 8 cyclones, which indicates the devastating situation in the Sundarbans.

Findings:

• This study assessed that Bangladesh is facing cyclones almost once a year, but the Sundarbans have been facing cyclones frequently for a decade. Among them, only the strong cyclone significantly destroys the Sundarbans. Though these mangrove forests face devasting situations lots of times but these can re-generate their ecosystem. 

• The vegetation coverage of Sundarbans mangrove is so dense, so the vegetation index works significantly well. During the study period (1990-2020) the vegetation index was seen dynamically for every single cyclone. That means Sundarbans does need any man-made support to rebuild their eco-function. 

• During this study, it was found that mangrove forest vegetation analysis for natural disasters has been significantly hampered by tidal influences and cloud coverage. Using high-resolution radar active remote sensing data may solve these issues. 

• Based on 30 years of study, it revealed that the Sundarban's vegetation has statistically correlated with wind speed. Due to extreme speed during SIDR the change was noticeable among 8 cyclones. 

Abstract Goes to Here:

Rapid urbanization in South Asian cities has triggered significant changes in land use and land cover (LULC), degrading natural biophysical components and intensifying urban heat islands (UHIs). This study investigated the impact of LULC changes on land surface temperature (LST) and the role of biophysical indicators in enhancing urban resilience to thermal extremes. We used Landsat satellite imageries from 1993 to 2023, conducted a comprehensive analysis of LULC changes, and estimated LST variations at 6-year intervals in the Dhaka, Gazipur, and Narayanganj districts in Bangladesh. Afterward, we performed statistical analysis upon employing correlation, regression, and principal component analysis (PCA) techniques to summarize information. The results reveal that 339.13 km2 worth of urban expansion has occurred in last 30 years, with an average annual growth rate of 3.5%, accompanied by a substantial reduction in water bodies (−139.17 km2) and vegetation cover. Consequently, summer temperatures exceeded approximately 36.52 °C in dense urban areas. Also, the results highlighted the strong influence of built-up areas (BSI and SAVI) on LST, while vegetation (NDVI) and water indices (NDWI) exhibited a negative association. The findings emphasize the urgency of integrating green infrastructure and deploying sustainable urban planning policies to mitigate the potential adverse impacts of scattered urbanization in the face of climate change.

Abstract Goes to Here:

Urban heatwaves are a growing concern, especially in South Asian countries grappling with rapid urbanization and limited resources. While prior studies focused on the biophysical aspects of urban heat islands in this region, there is limited evidence of people's understanding of urban heat stress and its health consequences. This study aimed to investigate the perceived urban heat risk and associated health impacts in Bangladesh. A cross-sectional survey of 898 respondents from eight major cities in Bangladesh were obtained for this study. A substantial proportion of respondents regularly experienced urban heat stress but had limited awareness of heatwave reduction measures. Moreover, perceived physiological impacts were reported as being slightly more severe than psychological impacts. Urban heat was believed to affect daily activities, particularly transportation, and sleep/rest. Factors like respondent's gender, home cooling systems, and spending time outdoors intensified heat's physiological and psychological impacts on respondents. By contrast, student respondents, highly educated respondents, residents of traditional katcha houses, and respondents in good health reported milder effects from heatwaves. Respondents over 30 years of age and those with employment showed greater knowledge about ways to reduce the impacts of heat and were less affected by heat's psychological impacts. These findings can inform targeted interventions and guidelines for heat mitigation and adaptation in South Asian cities.