Effects of rapid urbanisation on the urban thermal environment between 1990 and 2011 in Dhaka Megacity, Bangladesh

This study investigates the influence of land-use/land-cover (LULC) change on land surface temperature (LST) in Dhaka Megacity, Bangladesh during a period of rapid urbanisation. LST was derived from Landsat 5 TM scenes captured in 1990, 2000 and 2011 and compared to contemporaneous LULC maps. We compared index-based and linear spectral mixture analysis (LSMA) techniques for modelling LST. LSMA derived biophysical parameters corresponded more strongly to LST than those produced using index-based parameters. Results indicated that vegetation and water surfaces had relatively stable LST but it increased by around 2 °C when these surfaces were converted to built-up areas with extensive impervious surfaces. Knowledge of the expected change in LST when one land-cover is converted to another can inform land planners of the potential impact of future changes and urges the development of better management strategies

Population evacuation: evaluating spatial distribution of flood shelters and vulnerable residential units in Dhaka with geographic information systems

The objective of this study was to evaluate the spatial distribution of flood shelters in relation to flood hazards in a resource-poor country. Flood hazard estimates were developed from multi-temporal flood-affected frequency and floodwater depth maps. It is intended that the results could support non-structural flood management. In addition, the location of vulnerable housing units was mapped and their accessibility to shelters was computed with the aid of spatial techniques using a geographic information system. A subset of the Dhaka Metropolitan Development Plan zone and Dhaka megacity, covering an area of 878 km2, was used as a case study since this area is likely to experience more frequent and intense flooding in coming years as a result of rapid urbanisation and climatic change. Using three different criteria, the study identified that a total of 5537 buildings, out of 6342 candidate structures, can be used as emergency shelters during floods, and approximately 145,000 dwellings (19.3 % of total residential units) of various types were located in places that are prone to flood. Further, many (3500 of 5537) of the identified shelters were not sufficiently close to vulnerable dwellings to protect approximately 496,000 potential flood victims during an emergency. There were 26.4 % of the total residents living in vulnerable housing units. In addition, 1098 flood shelters were distributed over five catchments in the study area, although in close proximity to vulnerable residents, do not have the capacity to house the number of people who could potentially seek refuge there. This study, the first of its kind in Dhaka, can assist urban planners and emergency managers in developing an effective evacuation plan for an imminent flood disaster as the city currently lacks any disaster management plan

Glutathione and its dependent enzymes' modulatory responses to toxic metals and metalloids in fish: a review

Toxic metals and metalloid are being rapidly added from multiple pathways to aquatic ecosystem and causing severe threats to inhabiting fauna including fish. Being common in all the type of aquatic ecosystems such as freshwater, marine and brackish water fish are the first to get prone to toxic metals and metalloids. In addition to a number of physiological/biochemical alterations, toxic metals and metalloids cause enhanced generation of varied reactive oxygen species (ROS) ultimately leading to a situ- ation called oxidative stress. However, as an important com- ponent of antioxidant defence system in fish, the tripeptide glutathione (GSH) directly or indirectly regulates the scav- enging of ROS and their reaction products. Additionally, several other GSH-associated enzymes such as GSH reduc- tase (GR, EC 1.6.4.2), GSH peroxidase (EC 1.11.1.9), and GSH sulfotransferase (glutathione-S-transferase (GST), EC 2.5.1.18) cumulatively protect fish against ROS and their reaction products accrued anomalies under toxic metals and metalloids stress conditions. The current review highlights recent research findings on the modulation of GSH, its redox couple (reduced glutathione/oxidised glutathione), and other GSH-related enzymes (GR, glutathione peroxidase, GST) involved in the detoxification of harmful ROS and their reaction products in toxic metals and metalloids-exposed fish