This book is the product of an international workshop supported by UNESCO and co-sponsors under the G-WADI initiative. G-WADI is UNESCO's Global Network for Water and Development Information for Arid Lands. It has the strategic objective of strengthening global capacity to manage water resources in arid and semi-arid areas and seeks to provide a global forum for the exchange of experience, information, and tools. Its specific objectives include:

• improved understanding of the special characteristics of hydrological systems and water management needs in arid areas;

• capacity building of individuals and institutions;

• broad dissemination of understanding of water in arid zones to the user community and the public;

• sharing data and exchanging experience to support research and sound water management;

• raising awareness of advanced technologies for data provision, data assimilation, and system analysis;

• promoting integrated basin management and the use of appropriate decision support tools.

Information on G-WADI products and a news-watch service can be found on the G-WADI web-site (www.g-wadi.org).

Hydrological modelling is playing an increasingly important role in the management of catchments with respect to floods, water resources, water quality, and environmental protection. G-WADI identified a particular gap in the information available to support hydrological modelling for arid and semi-arid areas and hence designed an international workshop, bringing together some of the world's leading specialists in data products, modelling and arid-zone hydrology, to provide state-of-the-art material to workshop participants from arid regions world-wide, including South America, the Middle East, North Africa, Southern Africa, Australia and, particularly, Asia, where the workshop was hosted.