Water The abundant resource or a planners headache

Water, so critical to life on our planet, is everywhere, but unevenly so. Its fickle nature - water falls and flows when and where it chooses - hinders long-term planning for its availability and use. Globally, the water cycle provides about 40,000 cubic kilometres of renewable fresh water annually (Shiklomanov, 2000); but such a number is of little value to the water resources planner in a country or at the local level since the differences in rainfall, evaporation (from land and water) and transpiration (from plants)1 vary greatly by region and over time. Some regions experience heavy precipitation for parts of the year followed by long stretches of near total dryness (monsoonal and some temperate climates), while others such as Africa's Sahel region have large multi-annual or multi-decadal variability. Only some parts of the temperate zone enjoy fairly stable and reliable precipitation and benefit from low evapotranspiration.

The basin, national or local scales are more relevant for water resources planning. The water available in a basin (whether rain or water in a river, the soil or underground) is what humans and nature can access and use. Understanding the seasonal, annual and long-term variability at the basin scale is therefore essential for good management and planning.

In the basin, water's mobility challenges us. Water, both surface and groundwater, moves continuously through the basin landscape, although for planners, reality is different. Water boundaries do not define political borders; yet water availability in a country or a part of a country is reported according to the political boundaries. Thus, for most planners it is the city, district, county, provincial or national political divisions that serve as the starting point for most water management policies and strategies.

Complicating this is that water is often shared by countries. Rain is the dominant water source in some countries (in the temperate zone, or the most upstream country in a river basin); but for others it is the inflow of water from upstream countries that dominates (Egypt receives 97 per cent of its available water resources from upstream countries in the Nile Basin). This transboundary dimension greatly affects the degree of control and freedom of use in planning.

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