100 M. Smith Agricultural and Forest Meteorology 103 2000 99–108
1. Introduction
The great challenge for the coming decades will be the task of increasing food production to ensure food
security for the steadily growing world population, par- ticularly in countries with limited water and land re-
sources. While on a global scale water resources are still ample, serious water shortages are developing in
the arid and semi-arid regions. An increasing number of countries face serious water deficiencies as exist-
ing water resources are fully exploited. The depen- dency on water for future development has become a
critical constraint for development. Over 30 arid and semi-arid countries are expected to be ‘water scarce’ by
2025, meaning an annual water availability of less than 1000 m
3
per capita annually, which will slow down de- velopment, threaten food supplies and aggravate rural
poverty. The situation is aggravated by the declining quality
of water and soil resources, caused to a great extent by human activity. There is an urgent need to arrest this
human-induced degradation of water and soil resources and reclaim those that have been already degraded in
order to meet the present and future food requirements and other needs of the human population.
To focus attention on the growing problem of wa- ter scarcity in relation to food production, the World
Food Summit of November 1996, drew attention to the importance of water as a vital resource for future de-
velopment. Within the framework of the UN Agenda 21, FAO is closely cooperating with other agencies of
the United Nations to address this important issue. A global initiative for concerted action is established in
the Global Water Partnership where national and inter- national agencies and institutions from different sectors
are working together to find solutions for a looming global water crisis.
The concepts and options that can lead to a more effective use of water for crop production are reviewed
in this paper. Estimation of crop water use from cli- matic data is an essential element to achieve better wa-
ter use efficiency. The new perceptions included in the revised FAO guidelines on crop evapotranspiration will
contribute to this. Practical examples are presented to demonstrate in which way more effective planning and
management of irrigated and rainfed agriculture can be achieved. The compilation, processing and analy-
sis of agrometeorological information is a key element in this. Further studies to obtain a better insight in the
interaction between climate and water for crop pro- duction need to become a well defined priority area for
agrometeorological activities.
2. Water for crop production
