Md. Mujibur Rahman

Analyzing the Future Monthly Precipitation Pattern in Bangladesh from Multi-Model Projections using both GCM and RCM

ABSTRACT It is very much essential to comprehend the inter-relationship of future possible trend of precipitation with the water-stress problems in a small country like Bangladesh, since enormous challenges associated with water supply are already present in this region. A major dimension of climate change for Bangladesh includes the expectation of more intensive and variability of precipitation events in future times. There are a number of mathematical models of global circulation that indicate expectations of future climate scenarios. But one particular model does not produce a perfect projection of future climatology or observations as the inherent physics and associated underlying assumptions of the model-components might be different for different climate models. As such, it is best to combine several climate models to enable a choice to produce the most appropriate projection to be used in climate-scenario generation for a small geographical area. This paper features the development of Multi-Model combination of future precipitation projections for Bangladesh on monthly basis, for each of the year from 2011 to 2100, using both global and regional climate models. Four selected IPCC ensemble Global Climate Models (GCMs), namely CGCM3.1, CCSM3, MIROC3.2 and HadGEM1 as well as a Regional Climate Model (RCM) called PRECIS have been applied in this regard. The multi-model average precipitation changes for Bangladesh at SRES A1B scenario indicate that the precipitation might continue to increase in all the months in future years. Percentage of precipitation increment is expected to be quite higher for dry and pre-monsoon months compared to the monsoon season. Also, the large

Application of RCM-based Climate Change Indices in Assessing Future Climate: Part II- Precipitation Concentration

A major dimension of climate change for south-Asia includes more erratic precipitation events, precipitation being highly intensive with large variability in individual months. Such aberrant characteristics of precipitation are gradually resulting consequences of multi-dimensional impacts. This paper demonstrates the spatial variation patterns of extreme precipitation conditions in Bangladesh, based on a precipitation-related climate change indicator called Precipitation Concentration Index (PCI). First, the monthly total precipitation records from 18 meteorological stations in Bangladesh are applied in calculating PCI within a 30-year study period of 1981-2010. Then the same index is simulated using a RCM projected precipitation values in the future time scale of 2071-2100. The spatial variation of PCI has been plotted applying GIS technique for three distinct seasons, exhibiting drastic seasonal deviations with significant regional differences between the two independent timesegments. Comparison of the two periods proves prominent increase of PCI values all over the country invariably in each season. Numerically, the RCM-based PCI denotes that precipitation during 2071-2100 might become uniform to moderately concentric in monsoon, little change of precipitation concentration is expected in premonsoon and strong irregular distribution might reach its pinnacle for dry months. Therefore, such simulation of precipitation concentration index can be effectively applied as a decision support tool for erosion and drought adaptation.

Temporal variation characteristics of flow and water level in the Old Brahmaputra River

The principal objective of this paper is to assess the variability of water level and flow of the Old Brahmaputra River. The water level and Discharge trend of the river has been assessed based on historical data to find the variability over time. Average monthly discharge at a particular gauge station of the river has been plotted for the duration of 1975 to 2006 for each of the month to have an observed flow trend characteristics through time. The trend lines show that the river has undergone a considerable declination during the period. The wet period show large fluctuations of flow in a range of 2200 to 500 m3/s with a sharp decreasing pattern. The wet period flow of Old Brahmaputra River shows relatively lower discharge almost in every alternative year and its declination is radical compared to dry period flow. Alike discharge pattern water level also shows decreasing trend. Frequent fluctuations of water level are observed during the period from 1991-2008 when it shows more dispersive nature in the monsoon months. This declination of water level is observed to be faster during 1991-2008 than 1973-1990.

Experiment and prediction of a cavity type separated flow

A detail study involving flow visualization, Laser Doppler Velocimeter (LDV) measurements and numerical prediction is presented. The visualization experiments revealed striking results of a pulsatile motion in the separated flow region associated with the formation and passage of large eddy structures. Measurements of mean velocities and turbulence intensity profiles across the separated flow field, provided information about the separated shear layer development and the recirculating flow pattern. The numerical predictions, obtained with a two-layer turbulence model in conjunction with the SIMPLE algorithm, failed to reproduce the coherent eddies and the pulsatile motion, but the mean velocities are reasonably reproduced.

Application of RCM-based Climate Change Indices in Assessing Future Climate: Part I- Temperature Extremes

ABSTRACT Temperature variability appears to be a major aspect as a consequence of extreme climatic changes. South Asian countries have been observing an increase in occurrence of extreme climate events in recent decades. This paper demonstrates the temporal as well as spatial variation patterns of extreme temperature conditions in the North-western region of Bangladesh, based on some temperature-related climate change indices involving Average Monthly Maximum and Minimum Temperature (Tmax and Tmin). The analysis of the paper is divided into two fold aspects. First, the average maximum and minimum temperature records from 5 meteorological stations situated in the North-western region are applied in calculating the indices, within a 30 year study period of 1971 to 2000. Then the same indices are calculated using a Regional Climate Model (RCM) temperature projections in the future time scale of 2071-2100. Comparison of these indices shows significant enhancement in temperature extremes in future times. The indices validate marked increase in Tmin value which influences the most in overall warming in North-western region both in the past reference period 1971-2000 as well as in 2071-2100. The spatial variation of these indices also shows drastic difference in the distribution of the indices in 2071-2100, compared to the climatological baseline of 1971-2000. Therefore, such simulation of indices on temperature extremes can play significant role in long-term planning for the preparedness of meteorological disasters and risk reduction in a region and to the globe as a whole.

Compensation for neglecting stator transients in power system models

ABSTRACT An accurate simple model of alternators for power system stability studies has been developed. The model is based on a detailed model [1] the validity of which has been verified earlier. The simplification is achieved by omitting stator and transmission line transients from the detailed model and introducing a compensation for the omission. It has been shown that the compensation has to be included at every time step. Since the order of the model is lower than the detailed one its computational speed is faster and memory requirement is less. The accuracy of the simple model including the compensation has been proved to be outstanding by comparing the results of the model with those obtained from the detailed model

A Multi-Model Ensembling Approach for Developing Plausible Country scale Climate Change Scenarios for Future

Climate Models are the main tools available for developing projections of climate change in the future. Due to the inter-model differences in internal physics and the process of parameterization of the variables, it is essential to consider the range of projections from different models rather than depending on projection of one climate model only. In this study, multi-model ensemble for future projections of hydro-climatic parameters in terms of precipitation and temperature is developed on monthly resolution for each of the year from 2011 to 2100 with respect to a baseline period of 1971-2000 for Bangladesh. Simulations of four Global Climate Models (GCMs) named CGCM3.1, CCSM3, MIROC3.2 and HadGEM1 are applied for this purpose. An ensemble technique comprising Root Mean Square Error (RMSE) and Weight Factor has been thoroughly discussed. In line with this method, larger weight or preference is given to the GCM that has less error with respect to the observed temperature and precipitation values in the baseline. Prominent large scatters have been observed in the time-series plots for monthly multi-model ensemble precipitation, which resemble highly intensive and more inconsistent temporal precipitation pattern in future. In addition, mean surface temperature is likely to increase invariably in every month.