Simulation of Intensity, Track and Landfall of Tropical Cyclonic Storm Roanu over the Bay of Bengal Using WRF-ARW Model

Almost every year, tropical cyclone forms over the Bay of Bengal in pre-monsoon and post-monsoon which strikes Bangladesh coast and the east coast of India. As the full thermodynamic features of a cyclone is not solved yet, an attempt has been made to simulate the track and landfall of cyclonic disturbances over the Bay of Bengal by using Weather Research and Forecasting (WRF) model. The WRF model (version 3.8) was run in a single domain of 20 km horizontal resolution. The model was run using WRF Single-Moment 3- class microphysics scheme, Kain- Fritsch (new Eta) cumulus physics scheme, Yonsei University planetary boundary layer scheme, revised MM5 surface layer physics scheme, Rapid Radiative Transfer Model (RRTM) for long-wave and Dudhia scheme for short-wave scheme. The model was run for 24-h, 48-h, 72-h and 96-h using the National Centre for Environmental Prediction (NCEP) high-resolution Global Final (FNL) Analysis 6-hourly data using initial and lateral boundary conditions. The model simulated landfall position errors are found 53 km, 129 km, 119km and 23 km and time errors are found 02 E, 06 D, 02 E and 00 for 96-h, 72-h, 48-h and 24-h model run respectively (E indicates Earlier and D indicates Delay). The minimum time and position error is found in 24-hrs simulation. The spatial distribution is captured by the model is almost appropriate but the computational station rainfall is found less than that of observed rainfall. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 33-45

Climatology of Frequency, Life Period, Energy and Speed for Tropical Disturbances and Cyclones over the Bay of Bengal

Tropical disturbances and cyclones are regularly formed at the Bay of Bengal basin. There are some common traits in them, albeit each one of them is unique. Discerning climatology for the basic features of any tropical cyclone is useful in numerous ways. This research has attempted to find a climatology for frequency, life period, energy, and speed for the tropical cyclones formed at the Bay of Bengal over a period of 31 years – from 1990 to 2020. The results elicit that there are marked changes in these aforementioned features. The total frequency, accumulated duration, and combined energy have escalated over the years. To be precise, these changes have taken effect more rigorously for the Post-monsoonal tropical cyclones. The overall translational speed has slightly diminished in recent years, except for the translational speed of cyclones formed during Pre-monsoon. These changes will have major ramifications on the lives and livelihoods of people, more so for those living in coastal areas. Hence, necessary actions are required to cut the probable losses and damages. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 23-31

Species Composition, Abundance and Diversity of Phytoplankton Inhabiting around the Swatch-of-No-Ground of Northern Bay of Bengal

This study aimed to estimate the abundance and diversity of phytoplankton at different depth of water columns in Northern Bay of Bengal, Bangladesh. Samples were collected from 24 stations using Niskin water sampler from 0 to 250 m depths in four different cruises from January, 2017 to January, 2018 with the collaboration of Bangladesh Navy. Before sample identification, the samples were subjected to preservation using Lugol’s solution. A total of 70 phytoplankton species were identified of which Bacillariophyceae, Dinophyceae and Chlorophyceae covered 74.28%, 21.42% and 4.28% of species, respectively. The average phytoplankton density was 12,238±7,281 cells/L. Results showed phytoplankton abundance and distribution was comparatively lower in higher water depth than surface water. The highest phytoplankton abundance (39,342 cells/L) was recorded at surface water and the lowest abundance (16 cells/L) was observed in 200 m depth. Phytoplankton abundances significantly reduced at higher water depths (p < 0.05) which might be associated with higher light and nutrients availability at surface water and mixed layer depth. However, there was weak negative correlation since r = - 0.33. Phytoplankton abundance was also varied from station to station at similar water depth. Species richness was the highest in surface water. In this study, estimated Shannon-Wiener index was 0.58 that represented phytoplankton was moderately distributed at surface water than higher depth. The findings of the present study might be used as a baseline study to understand the phytoplankton community of the Northern Bay of Bengal which directly and/or indirectly help to manage existing ecosystem and sustainable fisheries of the Bay of Bengal. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 11-21

Development of Tropical Cyclone over the Bay of Bengal during South West Monsoon

South West Monsoon (SW Monsoon) and Tropical Cyclone (TC) are two important weather systems for Bangladesh. During SW Monsoon i.e. during rainy season Bangladesh gets 70% to 85% of her annual rainfall. TC accompanied with strong gale winds, tornadoes, torrential rains and storm surges is considered as a deadly natural disaster. TC’s are mostly formed during pre-monsoon and post-monsoon season, but not uncommon during SW monsoon. This study consults the best track data (cyclone e-atlas) of India Meteorological Department (IMD) containing tracks of cyclones and depression over North Indian Ocean (NIO) for the years 1891 to 2020 i.e. of 130 years. In these 130 years, among total 1219 storms, 608 had formed during SW monsoon. If only Cyclonic Storms (CS) and Severe Cyclonic Storms (SCS) are considered then, 150 storms formed during SW Monsoon. This paper studied two cyclogenesis factors; vertical wind shear and upper level anticyclone for eight cases of tropical storms formed during SW Monsoon. Besides cyclogenesis factors, influence of Madden Julian Oscillation (MJO) is also studied. Threat analysis associated with tropical storms during SW Monsoon has been done which might help in planning of National Disaster Management Program. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 57-65

Petrophysical Reservoir Characterization of Habiganj Gas Field, Surma Basin, Bangladesh

The previous studies on the petrophysical and volumetric analysis of Habiganj gas field were based on limited well data. As the accuracy of volumetric analysis relies greatly on petrophysical parameters, it is important to estimate them accurately. In this study we analyzed all eleven wells drilled in the Habiganj field to determine the petrophysical parameters. Analysis of the well logs revealed two distinct reservoir zones in this field termed as upper reservoir zone and lower reservoir zone. Stratigraphically, these two reservoir zones are in the Bokabil and Bhuban Formation of Surma Group. Petrophysical analysis shows significant differences between the two zones in terms of petrophysical parameters. Porosity in the upper reservoir zone ranges from 12% to 36%, with an average of 28%. This zone is highly permeable, as indicated by the average permeability of 500 mili Darcy (mD). The average water saturation in this zone is around 18% suggesting high gas saturation. The lower reservoir zone has an average porosity, permeability, and water saturation of 12%, 60mD, and 43%, respectively, indicating poor reservoir quality. An analysis of log motifs indicates that the upper reservoir zone is composed of stacked sands of blocky pattern. The sands in this interval are clean, as indicated by the lower shale volume of 12-15%. The average thickness of this zone is 230m, and the presence of this zone in all the drilled wells suggests high lateral continuity. The lower reservoir zone consists of sand bodies of serrated pattern. The sands have high shale volume and are laterally discontinuous. Overall, the upper reservoir zone has superior petrophysical properties to the lower reservoir zone. Although the reservoir quality of the lower reservoir zone is poorer than that of the upper zone, this zone can be considered as the secondary target for hydrocarbon production. Petrophysical parameters of this study were estimated from all the eleven wells drilled in this field; hence the values are more accurate. The reported values of the petrophysical parameters in this study are recommended to use to re-estimate the reserves in Habiganj field. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 1-10

Macrobenthic Faunal Abundance, Distribution and Diversity in the Bakkhali River, East Coast of Bangladesh

The study aimed to assess the macrobenthos abundance and distribution from the Bakkhali River, East Coast of Bangladesh. Macrobenthic and water samples were collected from the upper, middle and lower part of the river during post-monsoon. Several indices were used to find macrobenthos abundance and distribution and their correlation with water parameters were also assessed. Present study identified a total of 628 macrobenthos individuals representing 10 major taxa at three stations where 9 taxa were reported in both upper and middle parts whereas only 7 taxa were observed at lower stream of the river. The highest abundance of macrobenthos (301.04 indivs/m2) was recorded at the lower stream and the lowest abundance (166.3 indivs/m2) was found at the upper part of the river. Macrobenthos distribution showed that the number of Oligochaetes was higher (220 indivs) followed by Nemertinas (169 indivs) and Polychaetes (145 indivs). Study findings reveal that macrobenthos abundance and distribution were comparatively higher at the lower stream than the upper and middle part because of higher level of pollution and sendimentation rate that might influence the macrobenthos abundance and diversity in the upper and middle part. The study also found macrobenthos abundance was proportionally increased with increasing salinity and pH. However, macrobenthos abundance was decreased with increasing temperature. Simpson index (D) was the highest (0.32) at middle and lower part and the lowest (0.23) was in the upper part. Shannon-wiener index (H) was also higher (1.68) at the upper part. Both the indices showed higher diversity at the upper part because of having maximum taxa in the station. Based on the H value, this study reported that Bakkhali River was moderately polluted since H value was in the range of 1.44 to 1.68. These might be because of anthropogenic sources of pollution in the vicinity of the river. This study suggests to take proper management strategies to control aquatic pollution and conserve aquatic biodiversity. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 47-55

Distribution and Diversity of Macrobenthos in Sangu River, Bangladesh

This study was conducted to understand the macrobenthos distribution and abundance in Sangu River to monitor the aquatic pollution level. Both surface and sub-surface water and benthic sediments were collected from three stations of the Sangu River. A few indices viz. Shannon-wiener, Simpson, Margalef’s and Evenness were used to estimate the macrobenthic assemblages. In this study, a total of 11 major taxa comprising total 870 macobenthic species were identified. Shannon-wiener index was maximum (1.58) at lower part (LP) which indicated moderate to heavily pollute aquatic environment of the Sangu River. The average diversity values of Shannon, Evenness, Simpson and Margalef’s indices were 0.97, 0.43, 0.39 and 1.54 respectively. The concentration of dissolved oxygen was the lowest (4.90 mg/L) at LP and the highest (5.08 mg/L) at upper part (UP). This study showed that macrobenthos abundances was influenced by higher temperature, salinity, and pH. The percentage of organic carbon content was maximum (98.18%) at LP where the macrobenthic abundance was 330 individuals/m2, whereas it was minimum (80.77%) at UP where macrobenthic abundance was 248 individuals/m2 that indicated carbon content also influence the assemblages of the macrobenthos in the Sangu River. A clear gradient of physico-chemical and benthic soil parameters fluctuation was also found to be responsible for the variations of macrobenthos assemblage in the Sangu River. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 27-34

Trends of Rainfall and Temperature in Bangladesh: A Comparative Analysis of CMIP5 Results and Meteorological Station Data

The Coupled Model Inter-comparison Project phase 5 (CMIP5) dataset along with rainfall and temperature data, recorded at 34 stations of Bangladesh Meteorological Department (BMD), is analyzed to examine the recent changes in rainfall and temperature over Bangladesh during the period 1981-2019. In the historical period, all three CMIP5 models (MPI-ESM-LR, MPI-ESM-MR and NorESM1-M) underestimated the observed mean rainfall data collected from BMD, whereas for temperature the result is found to be nearly similar between model and observation. The result shows a trend of increasing mean maximum temperature of Bangladesh at a rate of 0.19°C and 0.26°C per decade and increasing mean minimum temperature at a rate of 0.18°C and 0.15°C per decade, for model and observation respectively. The study found a decreasing trend of annual rainfall in Bangladesh observed at a rate of 41.60 mm and 39.77 mm per decade, respectively, for model and observation. Spatial distribution shows an increase in annual rainfall in the northeastern part of Bangladesh. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 9-18

Lake Chad: Fluctuating Water Level and Its Implications for People’s Livelihood in the Area

This study assessed the fluctuating water level of Lake Chad and its consequences on the livelihood of people that depend on it. In terms of depth, Lake Chad is very shallow which makes it vulnerable to climate change and human activities. The study opined that continuous reduction in the volume of water of the lake will lead to negative effects such as forceful migration, resource-induced conflict, loss of biodiversity etc. Insurgency spear-headed by Nigeria based terrorist organization, “Boko Haram”, has killed many people including farmers and fishermen in the riparian countries of Nigeria, Niger, Chad and Cameroun and this has led to a decline in agricultural activities around the Lake Chad area making many to depend on food aid for their survival. The insurrectional activity of the terrorist group around the Lake Chad area also makes trade between communities extremely difficult as they are known to have attacked and killed people inside market. It is recommended that measures such as livelihood diversification through technology, creation of protected area, improved agricultural practices etc. should be adopted to reduce pressure on the lake and its resources. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 1-8

Presence and Antibiogram of Inhabiting Marine Bacterial Population at the Upper Sub-surface Water of the South East Coast of Bangladesh, Northern Bay of Bengal

The present study was conducted to assess the presence of bacterial populations at the upper sub-surface water from the offshore areas near the South East Coast of Bangladesh, the northern Bay of Bengal and to evaluate their antibiotic resistance pattern. Water samples were collected from 5 stations near the South East Coast of Bangladesh, the northern Bay of Bengal. About 38 marine isolates were primarily identified using conventional cultural methods (Mannitol Salt Agar, Chromocult Coliform Agar and Cetrimide Agar). Among them, two gram negative viz. Pantoea spp. and Pseudomonas aeruginosa and one gram positive viz. Micrococcus spp. were identified and confirmed by biochemical and analytical profiling index techniques. The antibiogram results showed that Pantoea spp. and Micrococcus spp. were sensitive to ciprofloxacin, tetracyclin, erythromycin and chloramphenicol, whereas P. aeruginosa was sensitive to ciprofloxacin, azithromycin and streptomycin. However, Pantoea spp. and Micrococcus spp. were resistant to at least 3 antibiotics (oxacillin, cefixime and polymyxin B). But P. aeruginosa was resistant to a number of antibiotics such as oxacillin, cefixime, ampicillin, novobiocin, cephalexin, tetracycline, amoxicillin and kanamycin. Increasing drug resistance potential of microbial organisms gives us signal to go for immediate necessary action on the maintenance of water quality of estuarine and coastal areas. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 35-44