Data collection

Knowledge of water availability and its distribution and variability in space and time is an essential prerequisite for a number of activities ranging from the forecasting of floods to the management of water resources and assessment of the potential impact of climate change. The collection and continuous supply of reliable and timely data, as well as the establishment and maintenance of historical data series, are basic requirements for acquiring information for planning and management purposes.

Inspite of the wide recognition that such information is needed, the past two decades have seen a worldwide decline in the coverage and reliability of systems for the collection of hydrological data.

To counteract this trend, WMO is supporting the National Hydrological Services in strengthening and updating their observation networks, in adopting modern data collection and transmission technologies and in developing their data management capabilities. The National Hydrological Services of WMO Members operate over 475 000 hydrological stations worldwide.

In addition to national projects, the main vehicle by which WMO supports the improvement of such information systems is the World Hydrological Cycle Observation System (WHYCOS). This is a global programme of WMO, structured into regional and national components, and aimed at improving countries' capacity to supply reliable water-related data to resource planners, decision-makers, scientists and the general public. Regional components of WHYCOS are presently being implemented in the Mediterranean Basin (MED-HYCOS), in Southern Africa (SADC-HYCOS), and in Western and Central Africa (AOC-HYCOS). Components for many other regions of the globe are in various stages of development.