Climate Changes over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences

Transcription

1 American Journal of Earth Sciences 2015; 2(6): Published online November 2, 2015 ( ISSN: (Print); ISSN: (Online) Climate Changes over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences M. A. Awal Laboratory of Plant Ecology, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh address To cite this article M. A. Awal. Climate Changes Over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences. American Journal of Earth Sciences. Vol. 2, No. 6, 2015, pp Abstract Averaged over a recent sixty years data, the national mean temperature and total annual rainfall of Bangladesh are found as C and 2400 mm, respectively. National mean temperature is higher than the temperature of Rajshahi and Sylhet divisions but lower than the Barisal, Khulna, Rangpur and Chittagong divisions. National rainfall is higher than the rainfall of Rajshahi (1592 mm), Khulna, Rangpur and Dhaka divisions but lower than the Sylhet (3182 mm) and Chittagong divisions. Around 60 percent of annual rainfall is occurred during summer months from June to August and rest is distributed to autumn and spring seasons whereas the winter from December to February received a few portion, 1 to 1.5 percent. Speculating to future climate, average temperature at all divisions throughout the seasons appears to increasing trend except Rajshahi where temperature in winter is appeared to decrease. Summer rainfall was found in increasing trend except Rajshahi, Dhaka and Chittagong divisions. Appearance of drought in northwest Bangladesh is the direct effect of low rain in that region. Sea-level rise, salinity intrusion and water congestion in coastal areas of Bangladesh are most important consequences of climate change. Proper adaptation and mitigation strategies are required to face such consequences of change in climate. Keywords Climate Change, Climate Stress, Drought, Global Warming, Rainfall, Temperature, Salinity, Sea-Level Rise, Water Logging 1. Introduction The change in the climate, also known as global warming, has occurred faster nowadays than ever. In other words, climate change is now more certain than ever (Hall, 2014). Global warming once ensured suitable temperature for the existence of life in this planet from its ice age or glacial periods (Crowley, 1995). The earth and it's climate have been constantly changing for millions of years. Still many parts of the world are getting benefits from climate change (Ridley, 2013). However, increased rate of global warming than its normal trend since about two centuries is the main source of the problem. The root cause of that increased global warming is the resultant effect of over increasing emission of greenhouse gases and exaggerated greenhouse effect. Nevertheless, most developed and industrialized nations are the big partners to emit such greenhouse gases where Bangladesh like other poor nations is only a silent victim of that negative effect (GPF, ; Karzon and Mehtab, 2006; CCC, 2007). As increased warming occurs globally, atmosphere of Bangladesh is also getting warm and consequently significant changes in the climate are gradually appearing over the country. Pattern of seasonal and regional distribution of rainfall is being changing over time due to global warming. As global warming occurs, sea level is gradually rising due to the melting of glaciers and expansion of water volume in the ocean. The timescales of ocean warming are much longer than those of surface air temperature rise. As a result, sealevel rise due to thermal expansion is expected to continue at a significant rate for centuries, even if climate forcing is stabilized (Meehl et al., 2005; Wigley, 2005). Rising sea level would invite a lot of uncertainties for the low-lying areas of the world. Coastal region of Bangladesh is under direct threat to sea-level rising as the elevation of southern reach of the country is low. Some other problems of the coastal areas of Bangladesh are salinity intrusion and water congestion due to high tide, storm surge etc. Sea-level rise may further

2 180 M. A. Awal: Climate Changes Over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences strengthen such negative impacts. Agricultural enterprises are under direct threat to climate change. Although the changes in climate occur slowly but the long-term effects of that change on crop production might be devastating. It is estimated that about 30 percent crop production will be reduced due to the climate change effect at this Century, and the production of rice and wheat would be reduced remarkably (IPCC, 2007). The IPCC has also predicted that due to global warming rice and wheat production will respectively be reduced about 8 and 32 percent by the year of Winter crop production would seriously be hampered due to warmer and drier environment. Moisture stress might force farmers to reduce the area under Boro (the Boro rice is commonly known as winter rice. The term boro is Bengali originated from the Sanskrit word "Boro" which refers to a cultivation from November to May under irrigated condition) cultivation (Selvaraju et al., 2006). Hence the issue of climate change is very crucial for Bangladesh as the country is mostly agrarian. Therefore, the aim of the study is to investigate the slow-onset changes in major climatic parameters occurred over the country. The consequence of the climate change on the various aspects of Bangladesh is another concern of the study. 2. Methodology The study is based on the analysis of secondary data sets. The historical data on air temperature and rainfall from 1948 to 2010 years recorded in 35 meteorological observatories throughout the country (Map 1) were collected from the Climate Division, Bangladesh Meteorological Department (BMD), Ministry of Defense, Government of the People s Republic of Bangladesh. These time series data were analyzed to division level with daily, monthly, seasonal and annual time scales. The division is the highest administrative unit of the country after national and there are only seven divisions like Barisal, Chittagong, Dhaka, Khulna, Rajshahi, Rangpur and Sylhet in Bangladesh that constituted from 64 districts. Future projection of temperature and rainfall was performed based on the time series data through linear extrapolation. Some other sources of collection of information are reviews of scientific documents, web browsing etc. Map 1. Meteorological observatories throughout Bangladesh.

3 American Journal of Earth Sciences 2015; 2(6): Results and Discussion 3.1. Overview of Major Climate Elements of Bangladesh Average temperatures in January vary from 17 C in the northwestern and northeastern parts to 21 C in the coastal areas of the country. Thereafter temperature rises, reaching the maximum in April, vary from about 27 C in the northeast to 30 C in the extreme west central part. After April, widespread cloud covers dampen temperature for subsequent seasons. Rainfall during winter season varies from less than 2 cm in the west and south to slightly over 4 cm in the northeast. As the winter season progresses into the premonsoon hot season, rainfall increases that varies from about 20 cm in the west central part to slightly over 80 cm in the northeast. The amount of rainfall in rainy season varies from 100 cm in the west central part to over 200 cm in the south and northeast (Source: Banglapedia; Map 2). Map 2. Climate elements of Bangladesh. Source: Banglapedia National Encyclopedia of Bangladesh. URL: accessed on July 31, Reprinted with permission.

4 182 M. A. Awal: Climate Changes Over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences 3.2. Slow-Onset Climate Course and Future Projection Climate is not a steady state matter rather its components are experienced to change continuously with time. Hence, year to year change in temperature and rainfall is a common phenomenon of climate for any region of the world and Bangladesh is not an exception Air Temperature Averaged over a sixty years data from 1948 to 2010, the national temperature is found as C which is higher than the average temperature of Rajshahi and Sylhet divisions but lower than the Barisal, Khulna, Rangpur and Chittagong divisions whereas the average temperature of Dhaka Division is similar to that of national average (data not shown). Average temperature at all divisions throughout the seasons appears to increasing trend except Rajshahi Division where temperature in winter is appeared to decreased (Fig. 1). The temperature distribution across regions and seasons found in this study is mostly similar to that of the temperature range in the climate element s map of Bangladesh (Map 2). Fig. 1. Mean air temperature since 1948 to 2010 across the divisions of Bangladesh. The future projection (with linear extrapolation) of temperature clearly shows that mean temperature of Bangladesh will be increased in all seasons; however the rate of increase of temperature would be greater in winter than the summer season. National mean temperature in annual scale will be increased 0.38 C by 2050 and 0.86 C by 2100 from its base value C at The corresponding increase of temperature in summer and winter seasons would accounted as 1.6 and 3.5 percent by 2050, and 2.7 and 6.1 percent by 2100, respectively. Temperature projection across the divisions and seasons shows the similar trend except Rajshahi where temperature in winter is projected to be decreased towards the coming days (Table 1). Our results on temperature projection mostly corresponds well with Agarwala et al. (2003) who found that mean temperature of Bangladesh is predicted to be increased, however the rate of increase of temperature would be greater in winter than the summer season. Predicted increased temperature may invite some extreme weathers like tropical cyclone with storm surge, tornado or nor wester etc. IPCC (2001) has also predicted that cyclone in the Bay of Bengal is to be formed more frequently due to increasing temperature, and there is evidence that the peak intensity of cyclone may increase by 5 to 10 percent.

5 American Journal of Earth Sciences 2015; 2(6): Table 1. Projection of mean temperature ( C) across the divisions in Bangladesh. Summer temperature ( C) Winter temperature ( C) Division Change on value Change on value National Barisal Chittagong Dhaka Khulna Rajshahi Rangpur Sylhet Rainfall The national rainfall averaged over a years is found as 2400 mm/year which is higher than the annual rainfall of Rajshahi, Khulna, Rangpur and Dhaka divisions but lower than the Sylhet and Chittagong divisions whereas annual rainfall of Barisal Division is near to national one (Fig. 2). Higher rainfall was occurred in Sylhet Division (3182 mm) followed by Chittagong division (2990 mm) whereas minimum rainfall was noticed in Rajshahi Division (1592 mm) followed by Khulna Division (1680 mm). Around 60 percent of annual rainfall is occurred during summer months and rest is distributed to autumn and spring months whereas the winter received a few portion, 1 to 1.5 percent. It is clear from monthly rainfall distribution that July received the peak rainfall in all divisions except Sylhet where highest rainfall is occurred during June (Fig. 3). In August, a small sudden drop in rainfall is occurred in all the regions except Chittagong and Sylhet divisions. In Sylhet Division, pre-monsoon rain starts quite earlier (from April) when higher amount of rainfall intercepts the region as compared to the other areas of the country that may cause early flood or flash flood in the locality. Wider monthly rainfall distribution especially prior to start of monsoon facilitates tea cultivation in Sylhet than the other regions of the country. Monthly rainfall distribution in Chittagong Division seems similar to that of national average but a heavy thrust of rain is occurred during peak monsoon from June to August. Fig. 2. Mean seasonal distribution of rainfall across divisions since 1948 to Winter, spring, summer, and autumn seasons represent the December- January-February, March-April-May, June-July-August, September-October-November periods, respectively.

6 184 M. A. Awal: Climate Changes Over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences Fig. 3. Mean monthly distribution of rainfall across divisions from 1948 to Fig. 4. Total rainfall from 1948 to 2010 across divisions.

7 American Journal of Earth Sciences 2015; 2(6): It is evident from Fig. 4 that total annual rainfall was in increasing trend except Rajshahi, Dhaka and Chittagong divisions. The increasing trend of rainfall in Sylhet Division was found much higher followed by Rangpur Division. It is speculated that more variability are associated with summer rainfall which is predicted (by linear extrapolation) to be increased in Sylhet Division as 8.7 and 19.6 percent by 2050 and 2100, respectively from its base value 1832 mm in 2010 (Fig. 5). In contrast summer rainfall in Rajshahi Division is projected to be decreased as 18.4 and 41.4 percent by 2050 and 2100, respectively from its base value 819 mm in It is alarming that decreasing summer rainfall especially in Rajshahi Division may invite the stronger drought event than the ever. On the other hand, predicted increasing summer rainfall may increase the flood risk or frequency in Sylhet Division. The amount of rainfall in Bangladesh is expected to be increased more about percent by 2030 and 27 percent by 2075 (CCC, 2011a). Increasing rainfall in summer season is considered to increase the flood events. It is predicted that by the year 2030, an additional 14.3 percent of the country would become extremely risk to floods, while the existing flood prone areas will face higher levels of flooding (CDMP, 2007). Division/Time National Barisal Chittagong Dhaka Khulna Rajshahi Rangpur Sylhet Winter Summer Spring Autumn Total rainfall (mm) Fig. 5. Season-wise rainfall projection in the different divisions of Bangladesh. Winter, spring, summer, and autumn seasons represent the December-January- February, March-April-May, June-July-August, September-October-November periods, respectively.

8 186 M. A. Awal: Climate Changes Over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences Sea-Level Rise (SLR) The SLR is an important slow-onset consequence of climate change for Bangladesh. The mean sea-level for Bangladesh is predicted to be increased about 14, 32 and 88 cm by the year 2030, 2050 and 2100, respectively (Agarwala et al., 2003; IPCC, 2001). In the Fourth Assessment Report, IPCC (2007) has predicted somewhat lower SLR than Agarwala et al. (2003). In the 4th IPCC Report, the sea level rise for different emission scenarios has not been given but a global sea level rise pattern for the IS92a scenario has been given and is shown in the Fig. 6. From that prediction it has been found that the global sea level will rise up to 59 cm in Fig. 6. Prediction of global sea level rise according to IS92a scenario (IPCC, 2007). Note: IS92a scenario is used as a reference from which to develop other scenarios. Global warming is raising sea levels around the planet by 2 3 mm each year. However, the distribution is not uniform due to ocean density and circulation changes. The sea-level rise along Bangladesh coast could be 0 5 cm more than the global average. It is found from satellite data analysis that relative sea-level rise is occurring for Bangladesh is 8 18 mm/yr whereas the tide gauge analysis from southwest Bangladesh found that mean sea level is climbing at 5 mm/yr, but high-tide level has risen by mm/yr in some spots (Schiermeier, 2014). In order to analyze the impacts of climate change on cyclonic storm surge along the Bay of Bengal, Ali (1999) considered 2 and 4 C increase in average temperature as lower and upper boundary thresholds (also defined as moderate and severe climate change scenarios by BCAS- RA-Approtech, 1994) for 2100, respectively. These two scenarios speculated a rise in peak monsoon rainfall by 18 and 33 percent that would cause an increase in river discharge during peak flow periods by 8 and 15 percent, respectively. The corresponding sea-level rise was speculated to be 30 and 100 cm, considering base sea level zero, with a corresponding rise in cyclonic intensity by 10 and 25 percent. Entire southern coastal areas including Sundarban mangroves of Bangladesh are vulnerable to sea-level rise as the elevation of the region is very low. Rising sea-level would certainly inundate more coastal land than that at present time which may aggravate the situation more vulnerable due to water congestion and higher concentration of salinity in soil. Bangladesh could face a catastrophic situation including permanent water congestion (i.e. long-term water logging situation that also occurs nowadays in the south-west Bangladesh) of about percent of its low-lying coastal areas (Al-Farouq and Huq, 1996). Specifically, the losses in agricultural production due to the inundation of about 128 thousand hectare crop land were noticed in Jessore, Satkhira and Khulna districts that directly affects the life and livelihood of about one million people (Awal, 2014). The CDMP (2008) and Climate Change Cell (CCC, 2011ac) of Government of Bangladesh (GoB) have predicted the following uncertainties due to the future sea-level rising in Bangladesh: i). In the coming days, primarily 120,000 km2 areas of the country will be inundated directly or indirectly due to the rise of sea-level as the elevation of those areas is lower; ii). About 32 percent areas of Bangladesh are the lowlying coastal areas, the land is housed about 35 million people who are at risk for future sea-level rising. It is expected that about 250, 227 and 180 km2 areas of Kutubdia, Bhola and Swandhip, of which 65 percent areas have already been gone under Bay of Bengal; iii). It is predicted that about percent land of Bangladesh will be inundated due to the sea-level rising of 45 cm (1.5 ft) by 2050 which may create 30 million climatic refugees/migrants from the coastal region of the county. Moreover, infrastructural development with all production systems of the inundated areas would be disrupted due to the loss of valuable agricultural land and displacement of local communities; iv). About 75 percent area of Sundarbans will be inundated due to 45 cm sea-level rising. All mangrove forests with Sundarbans will be affected due to the 1 m sealevel rising in Bangladesh at the end of this Century as a result people would deprive from the income sources at those regions; v). Due to sea-level rising, the loss associated with storm surge from future cyclone events will be more stronger; vi). The poor people of coastal belt who has no other land to build their houses will be more vulnerable; vii). The salinity problems in the coastal area of Bangladesh would further exacerbate due to SLR and reduced dry-season freshwater supply from upstream sources resulting from climate change (IPCC, 1998) Salinity Due to the climate change effect and consequent sealevel rising, southern coastal areas of Bangladesh are affected by salinity. Climate change exacerbates saline intrusion through several means such as the intrusion of

9 American Journal of Earth Sciences 2015; 2(6): the saline waterfront in the rivers, saline water interface in the groundwater aquifers, percolation from the increased saline surface waters into the ground water systems, and increased storm surges, which carry seawater inland (CDMP, 2007). In the dry season, saline water intrusion is occurred as much as about 100 km inside the Bangladesh from the Bay of Bengal along the tributary channels and rivers, and one-third land of Bangladesh (i.e. southern coast) is under tidal excursions (IPCC, 2007). About one million hectare cultivable land of Bangladesh becomes unsuitable for crop production especially in dry season due to the increased soil salinity (CDMP, 2008; Photograph 1). It is estimated that the salinity prone area of Bangladesh is being slowly increased over time. The salinity problems in the southern reach of Bangladesh would be compounded due to reduced freshwater supply during dry season from upstream sources resulting from climate change (IPCC, 1998) and some other anthropogenic reasons. It is predicted by the Bangladesh Climate Change Strategy and Action Plan (BCCSAP, 2009) of the Ministry of Environment and Forests of the Government of Bangladesh that within the next 50 years, over 20 million people could be displaced and become climate change refugees, if sea and salinity levels rise. Acknowledgments This paper is based on a study entitled Adapting social safety net programs to climate change shocks: issues and options for Bangladesh financed under the Research Grants Scheme (RGS) of the National Food Policy Capacity Strengthening Programme (NFPCSP). The purpose of the RGS was to assist in improving research and dialogue within civil society so as to inform and enrich the implementation of the National Food Policy. The NFPCSP is implemented by the Food and Agriculture Organization of the United Nations (FAO) and the Food Planning and Monitoring Unit (FPMU), Ministry of Food with the financial support of EU and USAID. The author is gratefully acknowledged Professor Ahmed A. Jamal, Managing Editor, Banglapedia, Asiatic Society of Bangladesh to give his kind permission for using a climate elements map of Bangladesh that made the article useful one. References [1] Agarwala, S., Ota, T., Ahmed, A. U., Smith, J., and Aalst, M. V., Development and Climate Change in Bangladesh: Focus on Coastal Flooding and the Sundarbans, OECD. [2] Al-Farouq and Huq, S., Adaptation to Climate Change in the Coastal Resources Sector of Bangladesh: Some Issues and Problems. In J. B. Smith et al. (eds) Adaptation to Climate Change: An International Perspective. New York: Springer- Verlag. pp [3] Ali, A., Vulnerability of Bangladesh to climate change and sea level rise through cyclones and storm surges. Water, Air and Soil Pollution 92: [4] Awal, M. A., Water logging in south-western coastal region of Bangladesh: local adaptation and policy options. Science Postprint 1(1): e00038; doi: /spp a0001. Photograph 1. Salinity affected fallow land in dry season in Shyamnagar Upazila of Satkhira District (southwest region of Bangladesh). 4. Conclusion Commensurating with global atmosphere, the climate of Bangladesh is also changing over time. Temperature is gradually increasing and predicted to be increased more to the future years. More variability is associated with rainfall, and consequently some regions of the country are at high risk to stronger drought events due to decrease of rainfall but some other regions to flood due to heavy rains. Entire southern reach is at high risk to sea-level rise, water congestion and salinity as the elevation of the region is much lower than the other part of Bangladesh. Proper adaptation and mitigation strategies are essentials as most changes in climate are beyond to human control. [5] BCAS-RA-Approtech, Vulnerability of Bangladesh to Climate Change and Sea Level Rise: Concepts and Tools for Calculating Risk in Integrated Coastal Zone Management (Summary report, Main reports and Institutional report). Bangladesh Centre for Advanced Studies (BCAS), Resource Analysis (RA), and Approtech Consultants Ltd., Dhaka. [6] BCCSAP, Bangladesh Climate Change Strategy and Action Plan. Ministry of Environment and Forests (MoEF), Government of the People's Republic of Bangladesh. [7] CCC, Climate change and Bangladesh. Climate Change Cell. Department of Environment (DoE), Government of the People s Republic of Bangladesh. [8] CCC, 20011a. Climate Change and Agriculture. Climate Change Cell, DoE, Paribesh Bhaban, Agargaon, Dhaka 1207, Bangladesh. [9] CCC, 20011b. Climate Change and Vulnerability in Bangladesh. Climate Change Cell, DoE, Paribesh Bhaban, Agargaon, Dhaka 1207, Bangladesh. [10] CCC, 20011c. Climate Change and Rice. Climate Change Cell, DoE, Paribesh Bhaban, Agargaon, Dhaka 1207, Bangladesh.

10 188 M. A. Awal: Climate Changes Over Bangladesh Delta: I. Slow-Onset Courses and Their Consequences [11] CDMP, Baseline Study on Disaster Risk Management and Climate Change Impacts Knowledge and Understanding among CDMP Stakeholders. Comprehensive Disaster Management Programme (CDMP). United Nations Development Programme (UNDP), Disaster Management & Tran Bhaban, Mohakhali C/A, Dhaka [12] CDMP, Climate Change and Bangladesh Risk Reduction and Adaptation. Comprehensive Disaster Management Programme, Climate Change Cell, DoE, Paribesh Bhaban, Agargaon, Dhaka 1207, Ministry of Food and Disaster Management (MoFDM), Government of the People s Republic of Bangladesh. [13] Crowley, T. J., Ice age terrestrial carbon changes revisited. Global Biogeochemical Cycles 9(3): [14] GPF, Climate Change. Global Policy Forum. URL: accessed on July 25, [15] Hall, S., Climate change is now more certain than ever, new report says. URL: accessed on July 25, [16] IPCC, The Regional Impacts of Climate Change: An Assessment of Vulnerability. Cambridge University Press. IPCC, Climate Change 2001: Impacts, Adaptations, and Vulnerability, Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change. McCarthy, J. J., Canziani, O. F., Leary, N. A., Dokken, D. J. and White K. S. (eds.). Cambridge University Press, Cambridge, UK. [17] IPCC, Climate Change IPCC Third Assessment Report (TAR). Contribution of Working Groups I, II and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK. [18] IPCC, IPCC Fourth Assessment Report (AR4): Climate Change Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK. [19] Karzon, S. H. R. and Mehtab, F. H., Critically looking at the just international environmental order from developing countries perspective. The Chittagong University Journal of Law XI: [20] Meehl, G. A., Washington, W. M., Collins, W. D., Arblaster, J. M., Hu, A., Buja, L. E., Strand, W.G. and Teng, H., How much more global warming and sea-level rise? Science 307: [21] Ridley, M., Why climate change is good for the world. Don't panic! The scientific consensus is that warmer temperatures do more good than harm. The Spectator, 22 Old Queen Street, London, SW1H 9HP. URL: accessed on July 25, [22] Schiermeier, Q., Floods: holding back the tide. Nature 508: doi: /508164a. [23] Selvaraju, R., Implementation of climate and agriculture programmes in developing countries. Workshop on improving resilience: Mobilizing solutions for adaptation, US State Department and US Environment Protection Agency (EPA), New Orleans, USA. [24] Wigley, T. M. L., The climate change commitment. Science 307: