Integrated and sustainable management of water, energy, food and ecosystems is challenging, even more so in transboundary river basins. The CGIAR Initiative on NEXUS Gains, one of two CGIAR Research Initiatives led by the International Water Management Institute (IWMI), recognizes that systems approaches – facilitating integration across sectors to identify positive synergies and manage trade-offs – are a prerequisite for sustainable development. The initiative promotes systems thinking to realize multiple benefits across the water–energy–food–ecosystems nexus.

As NEXUS Gains completes its first year, we highlight three of the initiative’s activities, which demonstrate why a systems approach is needed to tackle some of the most pressing global challenges.

Role of sand dams in an integrated storage network

Water storage is essential for building climate resilience and underpins many nexus interventions. To date, storage has largely been synonymous with man-made or gray infrastructure, such as dams and tanks, but there is growing interest in broader storage assessments which would also integrate natural or green infrastructure, such as aquifers and soil moisture. These storage solutions already retain large amounts of water and are of particular importance in semi-arid regions and with increasing climate change.

An assessment of water storage possibilities in the Shashe catchment – a sub-basin of the Limpopo River Basin shared by Botswana and Zimbabwe – indicated that sand dams present a promising yet underutilized water storage option. Sand dams – concrete barriers constructed in ephemeral sand rivers – combine gray and green infrastructure. Inflowing water is stored within the sand dam during the wet season; the sand reduces evaporation losses, and the water can be abstracted during the dry season.

In partnership with the Dabane Trust, researchers working under NEXUS Gains assessed the impact of 20 sand dams in the Shashe catchment. The results showed that the existence of sand dams ensured that water was available for an average of 4.4 additional months a year, and 3.9 additional months during a drought year.

While the study identified some risks to be investigated further, such as issues with the quality of abstracted water and infrastructure sustainability, the benefits suggest that sand dams are a promising innovation. Coupled with other storage options, sand dams can, in the right circumstances, play a key role in ensuring rural water security and building drought resilience.

Roadmap for solarization in Pakistan

South Asia is the global hub of solar irrigation, though it remains concentrated in India and Bangladesh. With funding from the World Bank, NEXUS Gains is developing a solarization roadmap for Pakistan’s Punjab region, where 95% of irrigation wells run on diesel. While the case for solarization seems clear, a nexus approach is essential for identifying, assessing and responding to the multiple trade-offs.

With no running costs, farmers can extract as much groundwater as they can access using solar pumps, potentially overexploiting and depleting aquifers. Through NEXUS Gains, IWMI has developed strategies to reduce the risk of overexploitation of aquifers. A key prerequisite to implementing these strategies is groundwater vulnerability mapping, which allows policymakers to customize solar irrigation business models and deploy strategies that fit local contexts.

Another innovation is the solar irrigation pump sizing tool, which calculates the optimum pump size for cropland–crop combinations, reducing the risk of overdesign with pumps that are too large or too small and fail to meet farmers’ needs.

In some locations, a feed-in-tariff offered to farmers can act as an instrument to manage groundwater and energy: during dry periods, higher tariffs can encourage farmers to use less energy (and groundwater) for irrigation, and instead feed surplus electricity back into the grid. This would contribute to the government’s renewable energy targets and enhance smallholder farmers’ climate resilience.

Whole systems solutions for Nepal

Globally, irrigation uses 70% of all water abstracted by humans. Even in a country such as Nepal, where water is abundant during the monsoon season, there is a growing recognition that irrigation water must be used more efficiently to ensure year-round water availability, for other sectors as well as for the environment.

To help the country better understand irrigation water use, researchers from NEXUS Gains partnered with government departments to gather data from three irrigation projects in Western Nepal. Although researchers concluded that there was sufficient water for irrigation, the water user associations and farmers consulted indicated that water was not being used efficiently and some stated they did not have enough water throughout the year.

Having analyzed the data, researchers identified a variety of reasons for this unavailability of water. For example, over-irrigation by farmers upstream leaves insufficient water for those downstream. This could be resolved with better management, plans and infrastructure, as well as enforcement of water allocation rules. Poorly planned maintenance schedules cause water supply issues during the dry months, while a lack of awareness of irrigation requirements for different stages of crop development means that farmers are not optimizing irrigation schedules.

The findings demonstrated the need for collaboration between government entities responsible for irrigation and agriculture in order to optimize water use in food production. NEXUS Gains has also helped to enhance the capacity of policymakers in the country to include a nexus approach in the government’s new irrigation policy.

We gratefully acknowledge CGIAR for funding the CGIAR Initiative on NEXUS Gains.