Sir

In the Commentary “Agriculture of the future” (Nature 428, 215; 2004), T. C. Tso discusses the problems faced by China's agricultural sector and suggests several possible approaches to the problem of feeding the world's largest population. We support many of the suggested solutions, such as reducing farmers' costs, providing more funds for agricultural research and adopting new techniques to improve agricultural products.

However, we strongly oppose Tso's proposal to divert water from southwest China to its northern and eastern areas, especially the idea of diverting water from the ‘big U-turn’ of the Yarlung Zangbo river in Tibet.

The ‘big U-turn’ is located in the geologically fragile region of the Himalaya mountains where the Indian Plate meets the Eurasian Plate. The problems of geologic instability and frequent landslides alone are enough to make any huge hydraulic projects difficult or even impossible. Additionally, the Yarlung Zangbo is an international river, passing through China, India and Bangladesh. A diversion project will undoubtedly change the hydrological conditions, especially the volume of water available to the lower countries, and is likely to cause an international dispute. Moreover, the ‘big U-turn’ is located in one of the world's biodiversity hotspots. Tso's proposed water-diversion project would irreversibly damage the ecosystems of the world's deepest and longest canyon, particularly the aquatic fauna.

Finally, we believe that China's water problems would be best addressed by the adoption of sound water planning and management, water conservation and efficient irrigation techniques — not by large-scale diversions.