Issues Magazine

Adapting to Climate Change by Banking on Water Storage

By Matthew McCartney

Rainfall variability, a key constraint to agricultural production in many countries, is likely to be exacerbated by climate change. If planned and managed correctly, various forms of water storage can increase water security and help safeguard livelihoods and reduce rural poverty.

In recent months, extreme weather events have wreaked havoc around the world, such as floods in Australia, Pakistan, Brazil, Sri Lanka and the Philippines, and severe drought and very high temperatures in Russia. In all cases, people suffered greatly and agriculture has been badly affected.

A recent report launched by the International Water Management Institute (IWMI) warns that increasingly erratic rainfall related to climate change will pose a major threat to food security and economic growth, especially in Africa and Asia. The report recommends increased investment in diverse forms of water storage as an effective remedy. The reasoning behind this is that, just as modern consumers diversify their financial holdings to reduce risk, smallholder farmers need a wide array of “water accounts” to buffer against climate change impacts. In this way, if one water source dries there are others to fall back on.

Millions of farmers in communities that depend on rain-fed agriculture are already at risk from decreasing and erratic availability of water. Planning and managing water storage will become more difficult as a consequence of climate change, even where total rainfall increases.

An integrated approach is needed that combines large- and small-scale storage options, including the use of water from natural wetlands, water stored in the soil, groundwater beneath the earth’s surface and water collected in ponds, tanks and reservoirs. IWMI and its research partners estimate that up to 500 million people in Africa and India can benefit from such techniques in agricultural water management.

In Asia, where irrigation greatly expanded in recent decades, rain-fed agriculture is still extensive, accounting for 66 per cent of the total cropped area according to the IWMI study. In sub-Saharan Africa the proportion is far greater at 94 per cent.

Yet these are precisely the regions where rainfall variability is greatest and water storage infrastructure is least developed. Unless the uncertainties in rain-fed agriculture can be overcome through better water storage, many farmers in developing countries will face a losing battle with a more hostile and unpredictable climate.

The IWMI study advocates giving more weight to a continuum of small-scale storage options, citing strong evidence that, when such measures are well-planned, they can contribute significantly to local food security and economic growth. Field studies in various semi-arid environments, for example, have proven the effectiveness of using small planting basins to “harvest” water, together with targeted application of organic or inorganic fertiliser. In Zimbabwe, such basins have boosted maize yields whether rainfall is abundant or scarce, while in Niger they have permitted three- or fourfold increases in millet yields.

In the north-east of India’s Rajasthan state, the construction of about 10,000 water-harvesting structures – intended mainly to recharge groundwater – has made it possible to irrigate about 14,000 hectares, benefiting some 70,000 people. Previously, farmers barely had enough water to produce grains but can now grow vegetables and other cash crops as well. Similarly, the construction of more than 90,000 underground water storage tanks in China is benefiting a million farmers.

Case studies suggest that combinations of different storage options can be particularly effective. In southern Sri Lanka, the construction of a large water storage reservoir, which was then linked to five previously created small reservoirs, brought about a 400 per cent increase in crop production.

But in some places the results of major water storage initiatives have been uneven. In Ethiopia, for example, one study showed that groundwater wells and small dams reduced poverty by 25–50 per cent. However, in the country’s Amhara region most of the approximately 4000 water-harvesting ponds constructed from 2003 to 2008 were no longer functioning, mainly because of poor site selection, technical failures and weak community involvement in maintenance.

Governments need to assume greater responsibility for more integrated planning of water storage systems. In the past, storage schemes were often conceived in a piecemeal fashion at the local level that was based more on political expediency than on evidence. Well-planned water storage can help lift people out of poverty and provide them with an effective way to cope with climate change.

In many places, water will be the principal medium by which the impacts of climate change will be manifested in agriculture. Water storage in all its forms offers a way to manage risks during these times of increasing uncertainty.