Floods in the south, drought in the north: it is the same ecological challenge every year in China. This summer will be no different as the Yellow River turns into a trickle while the Yangtze River overflows. Yet this is only partly the result of natural forces; mismanagement of the two rivers is also to blame.
In the case of the Yellow River, which was so named because of the huge quantity of sediment it carries, the natural shortage caused at this time of year has been exacerbated by the growth of water-intensive industries and agriculture - and large population centres - downstream. Add to this overgrazing of prairies closer to the river's source and water-pricing schemes that sell water at below cost - providing no economic incentives for conservation - and the result is a river that often runs dry before reaching the ocean.
In the case of the Yangtze, which splits China down the middle and has been responsible for the loss of hundreds of thousands of lives and incalculable economic damage over the years, deforestation and soil erosion have worsened its destructive power.
China's answer to both challenges has been to build large, ambitious civil engineering projects. The damming of the Yangtze at the Three Gorges began in 1993 and will not be completed until 2009, at a cost of 180 billion yuan. Meanwhile, a plan to divert water from the south to the parched north is under way; its most technically challenging portion, the western route, may never be built, but the project has a 500 billion yuan budget approved by the State Council, and the middle and eastern routes are proceeding apace.
The nation's leaders are not alone in grappling with water supply and management issues. Around the world, many countries are waking up to the fact that water, as much as land or air, is an environmental resource that has to be conserved, renewed and managed carefully, and that failure to live up to these requirements has dire health and economic consequences. Unesco estimates that more than 1 billion people lack an adequate supply of water or access to clean water - and that Asia is home to 65 per cent of the former and 80 per cent of the latter.
Water is such an integral part of our economies and our everyday lives. It is needed for sanitation, to grow food, to sustain wildlife and to power electricity generators, including those now being installed at the Three Gorges Dam. The UN notes that diseases like malaria and dengue fever, which still affect far too many parts of the developing world, are made much worse by lack of access to clean water. Others have been sounding the alarm for years about how shortages will lead to military conflict and grain shortfalls.