Bangladesh: Slipping into the sea?

A slightly backwards post today, the film below is quite long, but gives an excellent introduction to the problems Bangladesh is having with Climate Change and particularly SLR. For those without the time to watch the film the main body of the post is below:

  

So why so much interest in Bangladesh? As the film suggests Bangladesh is stuck in the middle of SLR and flooding by its great rivers due to increased melting in the Himalayas as a result of climate change. It is often cited as the country most at risk of Climate Change, and essentially the majority of the country is one large floodplain (see below). Karim & Mimura, (2010) find that only a small rise in sea level could be catastrophic to significant areas of the coastal zone, and similar to the USA as mentioned in my recent post, storm surging during tropical cyclones could exacerbate this effect. From the map below it is clear that any SLR could lead to catastrophic flooding.

Land height above SL in Bangladesh. Source

As I mentioned in my post on groundwater depletion, the subcontinent is one of the areas that undertakes a lot of groundwater extraction which can lead to SLR. This is a further pressure on the country meaning SLR could have a greater effect with land subsidence leading to more area becoming at risk of SLR (Brammer, 2014). The majority of Bangladeshis rely on agriculture for their income, running subsistence farms. With the projected loss of land expected to especially hit agricultural areas, people will be squeezed out of their livelihoods (Dasgupta et al., 2007). 

Bangladesh at least has begun to implement a National Adaptation Programme of Action (NAPA), based on UN standards to try and have a country wide project to mitigate against climate change. However as one of the Least Developed Countries with a GDP/capita of just $1,211, they lack the funding to implement large schemes such as those seen in the Netherlands or other developed countries. Therefore as outlined in the NAPA it is likely that Bangladesh will be forced to rely on aid to implement any adaption or mitigation programmes. This raises the question which I have not touched on too often: the main contributors to the climate change that is causing SLR. Bangladesh has contributed very little to climate change in terms of greenhouse gas emissions, but will be one of the first countries to feel the catastrophic effects. Considering projections suggest 17% of the land area is expected to be submerged by 2050, displacing 18 million people in the process, this is a ticking time-bomb. The response of the government is considered by many to be inadequate, with dredging programs and building of levees possibly exacerbating the situation.

Pethick & Orford, (2013) present an interesting study that suggests rates of SLR in Bangladesh are not actually the critical pressure on Bangladesh, more that increasing population and the lack of available land, but that SLR will affect increasing numbers of people. They project SLR in Bangladesh to be significantly above the global average meaning even more people could be at risk in the near future. This is due to an expanding tidal range due to both GMSL rise and subsidence of deltas. The study appears somewhat doubtful in the magnitude of SLR but is clear in needing an integrated action plan to help adapt and mitigate to the problems Bangladesh face. This is supported by Brammer (2014) who believes SLR at its current rate will not make a massive difference to Bangladesh but population pressures are again the critical problem. 

For me it is apparent that population pressures are crucial in Bangladesh but the studies still downplay the potential impacts of SLR; many other countries have population pressure but Bangladesh's problem with SLR means it is one of the most at risk and SLR will continue to compound it.

Contributions to Sea Level Rise: Direct Human Impact

The past few posts have focused on the variety of contributions to SLC that are as a feedback response to Global Warming and the current climate change we are experiencing. This post looks at how humans directly affect SLC through water impoundment and reservoir building.

This is the least studied section of SLC due to significant uncertainties about the future levels of groundwater extraction and depletion (IPCC, 2013). Groundwater is extracted from aquifers for agriculture and supply water for urban areas. Its unsustainable extraction means aquifers are not replenished and therefore reduces water supply, and this has started to gain more attention in the press due to its effect on SLC.

Current situation

Groundwater depletion is assessed to currently contribute 0.57mm/yr to SLC, a significant increase since 1900 when it was only projected to have contributed 0.04 mm/yr (Wada et al., 2012). This increase is attributed to increased water demand as a result of increased population and more intensive farming methods. This also fits with Konikow (2011) who suggested since 1900 there has been an average of 0.11mm/yr. Church et al., (2011) found similar values to those of Wada et al., (2012) but found significant uncertainty (±27%) in these estimates as it relies on a combination of groundwater models and observations that are difficult to constrain. In addition there is significant global spatial variability (see graph below). 

Groundwater depletion since 1960 with individual regional depletion. Source

Possibly more importantly the majority of studies have noted a recent acceleration due to increased groundwater uptake. As the video below shows, groundwater depletion is increasing rapidly in India, an area of significant groundwater depletion (above) which will affect both SLC and water security. 

This is offset by increased water impoundment behind dams for hydroelectric power or as a water source. Dams are thought to have reduced sea level by up to 30mm since 1900, as a result of preventing water from the sea. This will have reduced the impact of mountain glacier melting (see previous post) but not to the extent to have a massive effect on SLC. The projected proliferation of dam building across the world, expecting a 25% in global dam building means water movement will be even more controlled (Zarfl et al., 2015).

The future

It is likely that for the next couple of decades groundwater depletion will continue to increase. Over the next 50 years some projections suggest it will be of equal importance of melting glaciers and ice sheets to SLR. However there will become a point where groundwater is so depleted (see graph below) to a point where groundwater extraction is limited. 

Past Groundwater depletion contribution to SLC (black) and projected future groundwater depletion contribution to SLC from a range of models. Source

This is riddled with uncertainty due to a lack of knowledge of current groundwater reserves. The more concerning aspect of groundwater depletion is the potential impact on water resources, many countries with limited resources and rapidly growing urban areas rely almost entirely on groundwater extraction for water and agriculture. The majority of studies suggest that all of the extracted water will eventually end in the ocean; however more recent research has put that figure at more like 80% (Wada et al., 2016). This would greatly decrease potential SLC contribution, and has suggested the IPCC projections of SLC as a result of groundwater depletion are overestimated by a factor of 3.