Coping with climate change requires a greater understanding of the options for water storage, writes hydrology expert Matthew McCartney.
The lack of water is a major cause of food insecurity and poverty among the world's poorest people. But for many, the problem is not water scarcity per se, but the inability to manage rainfall variability.
In Sub-Saharan Africa, for example, where 95 per cent of small farms are rain-fed, the low predictability of both the amount and the timing of rainfall makes farming extremely difficult. A lack of water storage severely limits the ability of poor farmers to cope with droughts and floods, and is estimated to cost the Ethiopian economy one-third of its growth potential.
Climate change is expected to increase rainfall variability in many places, even where the total rainfall is set to rise. As a result, water management will become more difficult and many poor farmers will have less water security and become increasingly vulnerable.
In such circumstances, even small amounts of water storage can support crops or livestock during dry periods, significantly increasing agricultural and economic productivity and enhancing people's well-being. Water storage has an important role to play in poverty reduction, sustainable development and adaptation to climate change.
But water storage solutions must be fit for purpose. Water resource planning often focuses on large dams — about 40 per cent of the world's 50,000 large dams are used for irrigation. But while many of these contribute significantly to economic development, many have also incurred significant social and environmental costs and adversely affected poor people.
For agriculture, dams are just one of a wide range of possible water storage options, both on the surface and underground, including natural wetlands, enhanced soil moisture, groundwater aquifers, ponds, tanks and small reservoirs.
None of these is a panacea. Each has its own niche in terms of technical feasibility, socioeconomic sustainability, institutional requirements and impact on both public health and the environment. Consequently, the impacts of different types of water storage on poverty can vary significantly depending on the geographical, cultural and political context.
Where these contexts are adequately considered, water storage solutions can be successful. In Burkina Faso and northern Ghana, for example, thousands of small reservoirs have been built to supply water for domestic use, livestock and small-scale irrigation. Many of these have helped communities adapt to living in dry areas, making a positive contribution to reducing poverty and improving livelihoods.
But elsewhere, storage development has usually occurred in a piecemeal fashion, largely through local initiatives and with minimal planning. It is generally characterised by absent or poor data management, insufficient communication with local stakeholders and water authorities, and the lack of any integrated planning.
Too often, this ad hoc approach has resulted in inappropriate storage solutions, manifested by silted reservoirs, dry boreholes and higher incidences of diseases such as malaria.
In 2009, for example, it was estimated that most of the 4,000 or so rainwater-harvesting ponds constructed by government and non-government agencies in the Amhara region of Ethiopia between 2003 and 2008 were not working or had stopped being used. This failure stems from a range of factors, including poor site selection, design and technical problems (such as inappropriate lining materials, leading to seepage), and a lack of commitment to maintenance.
As populations grow, rainfall becomes more variable and the demand for water rises, planning and managing water storage will become increasingly difficult.
In addition, all storage options are potentially vulnerable to the impacts of climate change. Longer droughts may limit the ability of measures to increase soil moisture sufficiently to grow crops. And ponds, tanks and reservoirs may not be full enough to support agriculture, or may be at risk of damage from floods.
Maximising the benefits and minimising the costs of water storage will mean tailoring solutions to a wide range of complex and inter-related hydrological, social, economic and environmental factors. But given the uncertainties presented by climate change, planning will also need to be much more flexible and integrated across a range of levels and scales.
Solutions that combine and build on the complementarities of different storage types are likely to be more effective and sustainable than those based on a single option. For example, combinations of surface and groundwater storage, or large and small reservoirs, can dampen mismatches between supply and demand, and have already been used successfully in some parts of India and Sri Lanka.
But without greater understanding of which types of storage are best suited to specific agro-ecological and social conditions, and in the absence of more systematic planning, many schemes will fail to deliver the intended benefits and may even increase the negative effects of climate change.
Future planning must be more evidence based. Studies are needed to help understand the social and environmental impacts of different storage options, the implications of scaling up small-scale interventions, and, critically, the reasons for the success or failure of past interventions.
Systematic methods for evaluating the suitability and effectiveness of different options, both individually and within systems, must also be developed.
Matthew McCartney is a hydrologist at the International Water Management Institute in Addis Ababa, Ethiopia.