Effects of Climate Change on monsoon in Bangladesh

Climate Variability and Change in Bangladesh

The global climate is changing and it is likely to change further over coming decades due to increasing concentrations of ‘greenhouse gases’ in the earth’s atmosphere caused largely by human activities. This will result in greater variations in weather patterns, a greater frequency of extreme weather events such as floods, droughts and tropical storms, and gradual rises in average temperatures and sea-levels.

Bangladesh is extremely vulnerable to climate change impacts because of its geographical location, high population density, high levels of poverty, and the reliance of many livelihoods on climate-sensitive sectors, particularly rural agriculture andfisheries. These impacts will be falling more heavily on the women and girls of Bangladesh.

Climate change therefore threatens both previous achievements and future efforts to reduce poverty in Bangladesh to date, particularly by reducing water and food security and damage to essential infrastructure during more frequent disaster events.

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Bangladesh has always been vulnerable to climate variability. This is due to its geographical features and location, high influence of monsoon and regional flow patterns, too much water in monsoon and too little water in the dry season, etc. These have significant effects on the socio-economic realities, i.e. population density, inequity and deprivation, poverty and per capita resource endowment, and development practices. The overall impacts on Bangladesh already are and will be significant since climate variability and change will significantly affect the hydrology. The location of the country in the regional setting is in itself an element of vulnerability by giving rise to climate extremes. Further, the regional aspects of water management put additional difficulty toward adaptation to climate change and climate variability. Since climate variability and change will significantly affect the hydrology. The location of the country in the regional setting is in itself an element of vulnerability by giving rise to climate extremes. Further, the regional aspects of water management put additional difficulty toward adaptation to climate change and climate variability.

Too much water during monsoon

The climate of the country is strongly influenced by monsoon. Though Bangladesh occupies only 7% of the combined catchment area of the Ganges-Brahmaputra-Meghna river basin, the country has to drain out 92% of the flow into the Bay of Bengal. Too much water in the monsoon period affects different sectors, livelihoods and food security. Climate change scenario projections show mean monthly rainfall may significantly change over normal (i.e. current variability). Monsoon rainfall may increase by 11% by 2030 and 27% by 2070.Also, the general rise in surface average temperature will increase by 1.3 degree C by 2030 and 2.6 degree C by 2070. The number ofrainy days will increase by about 20 days. Implication of these climate change scenarios is that about 18 percent of current lowly flooded areas will be susceptible to higher levels of flooding while 12 to 16 percent new areas will be at risk to inundation. On an average about a quarter of the country’s landmass is curretly flood prone in a normal hydrological year, which may increase to 39 percent, while the frequency of a catastrophic flood (affecting over two-third of the landmass of the country) could increase under climate change scenarios. Prolongedflooding can effectively reduce overall potential for HYV Aman production.

Too little rain during dry season

During the post-monsoon to pre-monsoon cycle, rainfall diminishes while temperature increases. Low rainfall runoff reduces river flows, consequently salinity penetrates along the coastal rivers. A combination of increased temperature and reduced rainfall results in an increase in evapo-transpiration, detrimental to crop growth. Drought prone areas in Bangladesh Under climate change scenario projections, already low rainfall in the dry season will be further diminished. However, winter and premonsoon temperatures will rise significantly. The following consequences are possible:

A sharp rise in evapo-transpiration and diminishing rainfall will further reduce available flows in rivers. As a result, salinity will penetrate inland, restricting choice for the most preferred crops. Also, the lowering of rainfall runoff will either limit irrigation or put increased economic constraints on the already poor farmer. Production of wheat, HYV Aus and Boro might no longer be economically suitable under climate change. Increased surface temperature will lead to release of more carbon from the topsoil, which in turn will reduce fertility of soils. Increased water demand for irrigation will lead to increased withdrawal from the already lean surface water systems leading to further decrease in lean season flow in the rivers. An additional quarter of a million hectare land will become affected by salinity, on top of the 3.05 million hectares already affected. This will force farmers to grow crops of economically lesser returns.