Five years’ ago I visited Tonle Sap, a large inland lake in the central part of Cambodia near to Angkor Wat. The lake is connected to the Mekong River by the Tonle Sap River, which depending on the time of year, will flow in different directions. This unique phenomena was only discovered relatively recently and is caused by the tremendous amount of glacial meltwater that flows down the Mekong River, during the summer months, originating from the Himalaya. The quantity of water is significant enough to raise the water level in the Mekong River to the extent that the Tonle Sap River essentially flows upstream, filling up the lake. This coupled with the large rainfall that engulfs Cambodia in the later part of the year results in the water levels in the lake rising by several metres each year.
Many Cambodians rely on the ecosystem of the lake for their lifestyle. People live in the so-called floating villages, and have to use boats at certain times of the year as their only means of transport. Many of the houses do not actually float but are built on tall stilts approximately 8m or so above the bottom of the canals that lead away from the lake. At the end of the ‘wet’ season water levels are normal up near to the floor of the houses but over the year the water levels fall to such an extent that the houses emerge onto dry land.
So at the end of November 2011, I remember visiting a beautiful lake, with high water levels and observing daily life in boats, boats and more boats. The colours and light were spectacular on the pristine clear water producing beautiful reflections on the water surface.
So move forward to December 2016 when I was expecting to have the same experience and you can understand my surprise that what we found were water levels approximately 5m below what I had seen previously with much of the village now on dry land. Instead of the clear waters, the water colour was a distinct muddy brown. Essentially it was the same time of year, only about 4 weeks difference in the season. So why the change?
The first aspect to note was that the wet season in 2011 was exceptionally wet resulting in very high water levels. Our guide in 2016 was still pointing out how high the water had reached during the 2011 season. The peak water level occurred towards the beginning of November in 2011 and while we didn’t observe the peak, it was still very high at the end of November. Secondly water levels do recede quickly and within the space of a few weeks water levels can fall by several metres.
Having said that water levels in 2015 and 2016 have been much lower than they have been historically. This is partly due to the fact that there has not been as much rainfall in Cambodia in the last couple of years but this is only part of the story as the glacier meltwaters also provide a significant contribution to the lake water. Due to global warming the glaciers are melting at ever fast rates so really the lake should be full of water regardless of whether there has been an overall drought.
Upon talking to a few local people it appears that there is less water flowing down the Mekong River in Cambodia and it is speculated that this is due to the dams that are being built upstream along the Mekong, in China. The Mekong River originates in Tibet and crosses other parts of China before flowing through Myanmar, Laos, Thailand, Cambodia and Vietnam. According to internationalrivers.org at the end of 2014 China had built seven hydropower dams on the upper Mekong River (known as Lancang in China) and had plans to build 21 more. This is already having a significant impact on water flows down stream in the Lower Mekong, affecting the lives of millions of villagers as the river floodplain, and therefore the prime agricultural land on which they rely, is significantly reduced. Another impact is the decrease in water temperature, which together with the reduced flow, affects the fish stocks within the river downstream, again having a negative impact on the villagers who live in the lower reaches.
It is easy to blame China for all of these problems but we need to step back before we cast the finger of blame. At the turn of the millennium China had a significant world polluter as millions of Chinese burnt ‘dirty’ coal to heat homes and their increased affluence put an ever-increasing demand for the generation of electricity. China originally built a significant number of coal-fired power station to keep up with demand for electricity. With this came global pressure to reduce carbon dioxide emissions and a drive towards green, renewable energy. China, for its part has taken up this challenge and the construction of the hydroelectric dams is part of this drive. China, along with much of the world, has a long way to go before the problems of climate change are solved. But we must start to think about the short-term consequences some of the alternative ‘green’ technologies have on people and the environment.
The Three Gorges Dam in China
But there is one more issue that needs to be considered which is a direct consequence of climate change. As weather patterns change and the glaciers melt more and more water ends up in the world’s oceans and essentially becomes ‘contaminated’ with salt. Increased heavy rainfall events such as the storms observed in the UK (and many other countries) over the last few years result in large quantities of water draining quickly into our rivers and out to sea without the chance for the water to infiltrate into the ground and recharge our aquifers (an important source of drinking water). With an increasing human population greater demand is being placed on our precious freshwater. Who owns the water? Is it ok for countries along the upper reaches of rivers to construct dams to store water if it means that people living further down the rivers lose their water source? This is something that the world will have to come to terms with. Europe and North America are unlikely to feel these effects any time soon but we are starting to see the consequences of these action already in Asia, the Middle East and Africa and signs are that these issues will only increase over time. What will happen when large numbers of people have reduced access to water? This is something that the international community will have to come to terms with.