Developing sustainable river basin management under a changing climate is particularly important for transboundary rivers. The rivers that feed the Aral Sea provide a classic example, flowing through the five countries of Central Asia. Some countries, such as Tajikistan, are home to the snow and glaciers that are the source of the Amudarya and the Syrdarya rivers. Others, such as Uzbekistan and Turkmenistan are considered downstream countries and extract more water than they contribute to Amudarya.

IWMI aims to reduce transboundary competition for water by improving water-use efficiency while strengthening regional water cooperation and the means to adapt to and mitigate climate change. The effort is vital, because irrigated agriculture is the foundation of the region’s economies, while at the same time, changing availability brings unprecedented challenges in meeting all the other growing demands for water.

Integrated river basin planning depends crucially on sound data about water availability and use. One of IWMI’s main activities in 2019 was to produce a better model of the hydrology of the entire Aral Sea Basin. The new model uses a combination of ground-based measurements of water flows with remotely sensed land-use maps and soil data, along with climate information. During testing, it proved accurate enough to improve predictions that could form the basis for future water resources management.

An important element in these models is the rate of water loss through evaporation and transpiration by plants. The standard method for estimating evapotranspiration requires several measurements, such as solar radiation, air temperature, wind speed and humidity. As there are few weather stations in Central Asia that can provide the necessary data, we investigated a simpler method, which uses only air temperature, in southern Uzbekistan. During most of the year, the method provides a sufficiently accurate estimate, except in the summer when the figures were too low. A simple modification to the calculation, however, makes it considerably more accurate.

In addition to models, we have also provided evidence to improve irrigation. In 2019, we reported on experiments to compare the impacts of three different methods of irrigation on cotton yields in the Karshi Steppe, Uzbekistan: traditional flooded furrows, gated irrigation pipes and drip irrigation. At the end of the season, drip irrigation had used less than half the water of flooded furrows. It had also produced a larger cotton crop from fewer seeds in a shorter time. Overall, the efficiency of drip irrigation was almost three times greater than conventional flood irrigation, with additional benefits such as lower fertilizer use and reduced runoff.

Clearly, cotton and wheat farmers would benefit more by using drip irrigation. However, that requires substantial investment. The water for irrigation is raised about 135 meters from the Amudarya River by a series of seven pumping stations. Currently, the pumping stations consume 70% of the budget of Uzbekistan’s Ministry of Agriculture and Water Resources and generate 420 kilotons of carbon dioxide (CO₂) equivalent per year. Part of our advice to the government is to support better irrigation technology rather than the provision of water. This shift would help adaptation to climate change while also mitigating 120 kilotons of CO₂ equivalent.

As a result of IWMI’s research, the Government of Uzbekistan agreed to expand the area of drip irrigation. It is offering a subsidy of 50% of the cost of drip irrigation equipment, and farmers who install drip irrigation are exempt from the land tax for five years. The government is also withdrawing energy subsidies from farmers who do not adopt drip irrigation, a further incentive. It is also planning other changes to improve water-use efficiency in the Karshi Steppe.

The sharing of reliable and agreed data is a crucial aspect of transboundary water management for informed decision-making and evidence-based management. To support this, in 2019, we released a series of Digital Diagnostic Atlases for three administrations in the area. The atlases compile biogeographic, economic and social information with predictions of a changing climate, and offer a sound basis for improved water planning and management.

IWMI’s research in Central Asia continues to provide the evidence needed to support climate change adaptation practices and resilience building throughout the region. Research objectives also include smarter agricultural water management bringing increased yields, freeing more water to restore ecosystem services and meet domestic water needs.

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This work is carried out under the United States Agency for International Development (USAID) Partnerships for Enhanced Engagement in Research (PEER) Cycle 4 project: ‘Mitigating the competition for water in Amudarya River Basin, Central Asia, by improving water use efficiency’ and is funded by USAID.

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