Jul 12, 2014

Asia - A Flood of Challenges: Climate Change and the Mekong Delta

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As loyal readers of ExSE have probably noticed by now, this site, at its core, is dedicated to Mekong River and the people who are connected to it. Thus it seems odd that so little attention has been given to the Mekong Delta on ExSE. As is the case with most international coverage of the Mekong, the upper and lower reaches of the river are largely ignored in favor of stories about hydropower projects and the livelihoods they will affect.

However, the challenges that the Mekong Delta (MKD) is currently facing and will face in the future are also serious. These challenges are directly related to global warming and are shared with other deltas, though the unique geography and ecology of the Mekong makes the consequences of climate change here even graver.

The Delta itself is an astounding place. Completely contained within the borders of Vietnam, the region is an agricultural powerhouse. The Delta accounts for half of Vietnam’s rice production, three-fourths of its fish catch and 70% of the national fruit harvest while occupying 36,000 square kilometers, only 12% of Vietnam’s total area. While much of the fish is consumed domestically, rice and fruit are shipped to countries in Southeast Asia and beyond, contributing to Vietnam’s status as the world’s second-largest rice exporter.
Historically, most of the 22 million inhabitants of the Mekong Delta have settled densely along the three main branches of the Mekong and 90,000 km of canals and waterways that crisscross the region, with boats greatly outnumbering cars. The Delta is a highly aquatic environment and the human inhabitants wholly depend on the local water resource regime for their livelihoods. Unfortunately for them, the region’s hydrology is changing rapidly.

Precipitation modification is one area that is affecting the MKD. According to projected data from the Delta’s Can Tho University, the rainy season in the 2030′s will start two weeks later on average and annual total precipitation will decrease by 20% when compared with measurements from  the 1980′s. In addition, the distribution of precipitation over the rainy season months of May through October has changed. There is now less rain during the early and middle stages of the season and heavier rain during the later months of August, September and October. This runs counter to the water needs of paddy rice.

Monthly Rainfall Distribution in the Delta: Changes between 1980′s and 2030′s

All across Southeast Asia, people rely on the May through August rice crop both for year-round personal consumption and outside income. Like many crops, paddy rice has specific water needs during each stage of growth. During the first stage, large amounts of water are needed to soften the fields for plowing. Much less water is needed during planting, but the required amount increases as the rice buds and finally flowers in late July andwhen the rice ripens in August, the need for water decreases. Traditionally, precipitation patterns and water needs of paddy rice correlated well, however this has changed in recent years. The new of pattern of drought in the first half of the rainy season and heavy rain in the later months unbalances the paddy rice cycle and as a result, farmers in the Delta have been experiencing lower yields of their most vital crop.
Along with precipitation distribution, the amount of rainfall the Delta receives is also changing. As mentioned before, modeling indicates that average annual precipitation the 2030′s will have fallen by 20 mm when compared with 1980 levels. Coupled with modified distribution patterns, farmers will be forced to resort to expensive water pumping and revised irrigation techniques in an effort to maintain yields. However, this drop in rainfall will be short-lived. Research done by the International Panel on Climate Change (IPCC) shows that this trend will reverse in the 2050′s and average precipitation will double by 2070, posing completely different challenges for farmers.

Predicted change in precipitation for 2030′s when compared with data from 1980′s.

Unfortunately, changing precipitation levels are not the only aspect of climate change that is affecting the Delta. Across the world, temperatures are increasing and southern Vietnam is no exception. Based on modeling by the IPCC the average temperature in the MKD will increase by 1°C between 2010 and 2039. Further modeling indicates that the Delta will become an oven by 2080, with average temperatures 3-4°C higher than 2010 levels. Furthermore, the annual number of days over 35°C is set to double by 2030, when compared with numbers from the 1980′s.

Aside from more active sweat glands and a boon for the air conditioner industry, these numbers have real consequences for the people of the Mekong Delta, especially because hotter temperatures affect their crops. According to research done in the last decade, the average minimum temperature of an area and its rice production are correlated; for every 1°C increase in minimum temperature, average rice yields fall by 10%. When coupled with the data on climate change in the MKD, the future of the region’s rice production is bleak. Average yields will decrease by almost 10% by the 2030s and by the 2080s, and the Delta’s rice production will only be 60% of its 2010 levels. In addition, changes in precipitation patterns might also have a negative effect on rice harvests, only exacerbating the impacts of rising temperatures.

However, Delta farmers in the 2070s may not have to worry about crop yields because by then, there might not even be fields to plant seeds in. There are two interrelated reasons for this possibility: salinity intrusion and coastal and riverbank erosion. Salinity intrusion poses a danger to agriculture because almost all crops, like rice and tropical fruit, need fresh water to grow; saltwater intrusion damages the water table and the land above it used for farming. In recent years, salinity intrusion has increased in intensity and scope. Comparing levels measured in 2005 and 2010, researchers from Can Tho University found that salinity intrusion more than doubled, reaching 70 km upstream. What used to be a problem only for the most coastal of Delta farmers has now become a danger to almost half the region.

With increased sea levels rise (SLR), saltwater makes deeper incursions into the Delta, leading to overall higher salinity levels (measured in grams/liter).

Rising sea levels and a changing river course both contribute to salinity intrusion.  Rising sea levels are a global phenomenon that has been well documented but its effects vary by location and the MKD is an especially hard hit area. It is ranked as the most vulnerable delta in the world by the IPCC, and with good reason as the Delta could lose significant portions of livable land in the coming decades. Based on geography and population distribution, the MKD will lose 25% of its land with one meter of sea level rise and a two meter rise will take away half. With livable land already scarce, just a one meter rise would leave 3.5 million Delta residents homeless.

As the sea levels rise, more salt water enters into the farmland, especially during times when high tides are stronger. Salinity intrusion is only exacerbated by the Mekong’s flow modification. Increased irrigation and a string of already-built and planned hydropower projects on the Mekong and its tributaries are decreasing the flow rate of the river in the MKD. This weakens the Delta’s capacity to resist incursions by the sea. What’s more, the same irrigation and hydropower projects also decrease the amount of sediment that reaches the Delta. Thus when the tides finally retreat from the Delta, vital nutrients that could help replenish the soil are lacking.

Unfortunately for the 22 million residents of the Delta and tens of millions more that depend on their crops, these are only a few of the environmental problems facing the region. Increasingly erratic flood cycles and intense tropical storms are just two more. Socio-economic problems also plague the region and from the look of environmental modeling, the window to solve these issues is rapidly closing. At the same time, such a dynamic environment offers great opportunities for study and experimentation, both of which could benefit delta regions globally. The forecast for the MKD is not good, but there are possible solutions, some more conventional than others. In the coming weeks, look for more discussion on the issues facing the Mekong Delta, only from ExSE.


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