Wednesday, September 29, 2010

Harnessing the benefits of groundwater

Source: International Water Management Institute 

This policy brief, published by the International Water Management Institute (IWMI), explores the role of groundwater storage in providing communities with wider access to water in the face of climate change.
The use of groundwater for domestic water and irrigation has already lifted millions of small farmers out of poverty. But, for many regions, including the world's biggest groundwater user, India, supplies are dwindling because of overextraction, pollution and growing competition for use from cities or hydropower.
Climate change will add to the pressure because the more variable rainfall predicted will inevitably further stimulate groundwater use but could change the natural rate of aquifer recharge.
A coherent strategy for recharging aquifers is essential to ensure groundwater supplies in a changing climate. There are several technical options for managing groundwater recharge, say the authors. These include direct surface methods, where water from reservoirs or canals seeps into aquifers, or where irrigation water is left to infiltrate into shallow aquifers. Subsurface methods include digging flooding pits or 'injecting' water into aquifers through deep boreholes.
The best results will often be obtained through a managed mix of seepage, infiltration and injection methods, say the authors. But achieving this will require policymakers and water managers to move towards co-managing surface water and groundwater, rather than treating the two as separate domains.
Co-management strategies could help, for example, in Central Asia, where competition between users has led to political conflicts, and where large-scale surface irrigation has resulted in waterlogging, soil salinisation and other environmental problems. Water supplies here could become more sustainable if farmers switch from using surface water to groundwater for their summer irrigation needs, and use the winter runoff to recharge aquifers before the next growing season.
With climate change, access to water will be increasingly vital for irrigation. Groundwater storage could provide the answer. Investments in relatively inexpensive engineering could enhance and stabilise groundwater aquifers to provide storage capacity that is both accessible to large numbers of small farmers when and where they need it, and is more resilient to dry spells.
The full policy brief was written by a team of IWMI researchers.