Launch disasters in Bangladesh: a geographical study

Bangladesh is a riverine country and communication by waterways is of great importance especially in the southern region of the country. From Chandpur southwards, waterway is the only means of transport and so a large number of people has to travel by motor launches in the coastal areas and inland. Since the early 1950's, motor launch services have become popular and in the period 1997-98 there were 1,853 registered launches operating 227 routes. But this important mode is ridden with tragic disasters every year, incurring a heavy toll of human lives. Since 1977, there were 248 motor launch accidents recorded by BIWTA (Bangladesh Inland Water Transport Authority) with a loss of 2,309 1ives, 374 persons injured and 208 persons missing. This paper attempts to roughly trace out the causes and the geographical distribution of the accidents through an analysis of a time series data covering the period between 1977 and 2000. It was found that the most frequent type or cause of launch accidents was collision, followed by foundering and overloading. The least frequent accident types were due to under-water currents, shoals, leaning electricity poles and country boats travelling without lights at night and manned by untrained operators, followed by cyclones. Interestingly, overcrowding did not seem to be the most typical of launch disasters in the countr

Spatio-temporal analysis of spatial accessibility to primary health care in Bhutan

© 2015 by the authors; licensee MDPI, Basel, Switzerland. Geographic information systems (GIS) can be effectively utilized to carry out spatio-temporal analysis of spatial accessibility to primary healthcare services. Spatial accessibility to primary healthcare services is commonly measured using floating catchment area models which are generally defined with three variables; namely, an attractiveness component of the service centre, travel time or distance between the locations of the service centre and the population, and population demand for healthcare services. The nearest-neighbour modified two-step floating catchment area (NN-M2SFCA) model is proposed for computing spatial accessibility indices for the entire country. Accessibility values from 2010 to 2013 for Bhutan were analysed both spatially and temporally by producing accessibility ranking maps, plotting Lorenz curves, and conducting spatial clustering analysis. The spatial accessibility indices of the 205 sub-districts show great disparities in healthcare accessibility in the country. The mean-and median-based classification results indicate that, in 2013, 24 percent of Bhutan's population have poor access to primary healthcare services, 66 percent of the population have medium-level access, and 10 percent have good access

Effectiveness of DOS (Dark-Object Subtraction) method and water index techniques to map wetlands in a rapidly urbanising megacity with Landsat 8 data

The objectives of this work were to examine the applicability of the Dark-Object Subtraction (DOS) atmospheric correction method and water-based index techniques to map wetlands in Dhaka megacity using Landsat 8 data. With the use of both raw data and DOS- corrected imagery, the analysis revealed that DOS- corrected images performed better in discriminating wetland areas. Furthermore, the Modified Normalised Water Index (MNDWI) was the most superior technique whilst the Normalised Difference Water Index (NDWI) was the least suitable in identifying the spatial locations of wetlands in a rapidly urbanising environment such as Dhaka

Mapping Informal Settlements Using Machine Learning Techniques, Object-Based Image Analysis and local Knowledge

The existence of informal settlements in Riyadh City, the Kingdom of Saudi Arabia (KSA), has given rise to some urban planning issues. To provide improvements to mapping and planning processes, the current study aims to evaluate and characterize informal settlements within the city using object-based machine learning (ML) techniques (specifically, Random Forest (RF) and Support Vector Machine (SVM)), expert knowledge (EK) and satellite data. An examination of four defined locales has produced a comprehensive, local, informal settlement ontology. Four main categories (shape, geometry, texture, and pattern) were used to build the ontological framework. Expert local knowledge was employed to produce a ruleset to accurately identify and map these areas. Specific indicators identified by the specialists were used in a combined object-based ML and image analysis (OBIA) approach, with high-resolution worldview-3 imagery used as input data. Results demonstrated that combining EK and ML with remotely sensed data can efficiently, effectively and accurately distinguish informal settlement areas. This work has shown that an object-based ML technique (RF), in combination with EK about important local environment indicators, provides a useful method for mapping informal settlements

Evaluating Flood Damage using GIS and RADARSAT data-A case of the 1998 Catastrophe in Greater Dhaka, Bangladesh

The objective of this paper is to delineate flood prone areas and estimate damage in Greater Dhaka during the 1998 catastrophic flood using an integrated approach of GIS and remote sensing. Time series RADARSAT SAR data is acquired and used to demarcate flood boundaries for the 1998 flood event. This was accomplished by thresholding linear SAR imageries. Flood estimation demonstrated that flood areas steadily increased from early July 1998 and peaked on 25 August 1998 inundating 53% lands due to heavy monsoonal downpour and discharge from upstream points. Different thematic layers were combined with a derived flood map in order to assess flood damage for the same event. Flood damage analysis revealed that substantial damage has occurred in Greater Dhaka during the 1998 flood

Remote Sensing of 1998 and 2000 Floods in Greater Dhaka, Bangladesh: Experiences from Catastrophic and Normal events

This paper is an attempt to develop a series of maps that precisely depict flood prone areas in Greater Dhaka, Bangladesh using remote sensing techniques. Multi-temporal RADARSAT SAR data were acquired and employed to delineate open water flood boundary during the floods of 1998 and 2000. Using a threshold algorithm, SAR data is segregated into water and non-water areas. The empirical threshold value was obtained by using visual interpretation technique, local knowledge of the study site and by deriving corresponding pixel values to land/water from each image. The result demonstrated that 53 percent of the study area was heavily inundated in 1998 flood which is the largest submerged area during a catastrophic scenario. In contrast, 35.32 percent area was flooded during the year 2000 which represents the area under water for a normal event. Using the reference data acquired from field visit, derived flood maps were further validated. Moderate accuracy is obtained for all flood maps, however, July 1998 image attained the highest overall accuracy (86%) in the dataset. The derived flood maps are expected to be useful to mitigate losses of lives and property from river water flooding in Greater Dhaka. Furthermore, this information would be worthwhile to develop an efficient flood disaster management system

Integrating satellite soil-moisture estimates and hydrological model products over Australia

Accurate soil-moisture monitoring is essential for water-resource management and agricultural applications, and is now widely undertaken using satellite remote sensing or terrestrial hydrological models’ products. While both methods have limitations, e.g. the limited soil depth resolution of space-borne data and data deficiencies in models, data-assimilation techniques can provide an alternative approach. Here, we use the recently developed data-driven Kalman–Takens approach to integrate satellite soil-moisture products with those of the Australian Water Resources Assessment system Landscape (AWRA-L) model. This is done to constrain the model’s soil-moisture simulations over Australia with those observed from the Advanced Microwave Scanning Radiometer-Earth Observing System and Soil-Moisture and Ocean Salinity between 2002 and 2017. The main objective is to investigate the ability of the integration framework to improve AWRA-L simulations of soil moisture. The improved estimates are then used to investigate spatiotemporal soil-moisture variations. The results show that the proposed model-satellite data integration approach improves the continental soil-moisture estimates by increasing their correlation to independent in situ measurements (∼10% relative to the non-assimilation estimates). Highlights Satellite soil-moisture measurements are used to improve model simulation. A data-driven approach based on Kalman–Takens is applied. The applied data-integration approach improves soil-moisture estimates

Environmental factors associated with the distribution of visceral leishmaniasis in endemic areas of Bangladesh: Modeling the ecological niche

Background: Visceral leishmaniasis (VL) is a parasitic infection (also called kala-azar in South Asia) caused by Leishmania donovani that is a considerable threat to public health in the Indian subcontinent, including densely populated Bangladesh. The disease seriously affects the poorest subset of the population in the subcontinent. Despite the fact that the incidence of VL results in significant morbidity and mortality, its environmental determinants are relatively poorly understood, especially in Bangladesh. In this study, we have extracted a number of environmental variables obtained from a range of sources, along with human VL cases collected through several field visits, to model the distribution of disease which may then be used as a surrogate for determining the distribution of Phlebotomus argentipes vector, in hyperendemic and endemic areas of Mymensingh and Gazipur districts in Bangladesh. The analysis was carried out within an ecological niche model (ENM) framework using a maxent to explore the ecological requirements of the disease. Results: The results suggest that VL in the study area can be predicted by precipitation during the warmest quarter of the year, land surface temperature (LST), and normalized difference water index (NDWI). As P. argentipes is the single proven vector of L. donovani in the study area, its distribution could reasonably be determined by the same environmental variables. The analysis further showed that the majority of VL cases were located in mauzas where the estimated probability of the disease occurrence was high. This may reflect the potential distribution of the disease and consequently P. argentipes in the study area. Conclusions: The results of this study are expected to have important implications, particularly in vector control strategies and management of risk associated with this disease. Public health officials can use the results to prioritize their visits in specific areas. Further, the findings can be used as a baseline to model how the distribution of the disease caused by P. argentipes might change in the event of climatic and environmental changes that resulted from increased anthropogenic activities in Bangladesh and elsewhere

A reflectance-based water quality index and its application to examine degradation of river water quality in a rapidly urbanising megacity

The water quality in rivers around Dhaka is deteriorating very fast given extensive sources of pollutants associated with rapid urbanisation and industrialisation. This paper introduced a water quality index (WQI) utilising Landsat bands 1 to 3 (0.45 to 0.67 µm) against band 5 (1.55 to 1.75 µm). The value of the proposed index varies from – 1 to + 1, whereby around 0 (small positive and negative) indicated probable contamination, if the water depth is around 2 m or above. This approach was developed using Landsat data to study long-term water quality change in the rivers surrounding Dhaka megacity, Bangladesh. The values were converted to total suspended solids (TSS) by utilising observed in-situ data, which showed a clear seasonal influence of water pollution, suggesting it reduces to the background level with the onset of high monsoonal river flows. However, long-term analysis showed that the rivers remain polluted throughout the year, particularly since 2011. The main reason for increasing river water pollution may be linked to the contaminant load which has increased extensively in recent years. The approach developed in this study may be used in other urban rivers, particularly in Asia

Characteristics of Damages of Severe Local Storms Based on Field Surveys in Bangladesh

This paper presents field survey results on damage from severe local storms, such as tornadoes. Surveys were conducted in Bangladesh in August 2009 and August 2010 to clarify damage details, meteorological features, factors related to damage generation and spread, recovery problems experienced by local residents due to storm damage and storms prediction in local areas