This special edition is a compilation of papers delivered orally at the workshop on regionalization of models for operational purposes in developing countries held during the joint International Association of Hydrological Sciences (IAHS) and International Association of Hydrogeologists (IAH) International Convention in Hyderabad, India during September 2009. The overall theme of the convention was ‘Water: A vital resource under stress – how can science help?’ How science can help solve practical water resources management problems and regionalization of models have been recurring themes in hydrological science over the last few decades. If anything, however, the gap between scientific developments and their application in practice has widened, notably in developing countries where financial and institutional constraints continue to be difficult to overcome. While data scarcity remains a major problem, a combination of developments in models, availability of remotely sensed data and an understanding of the treatment of uncertainty implies that we can overcome many of the data deficiency issues. Unfortunately, this does not seem to be the case in practice, and effective and sustainable technology transfer remains elusive in many developing countries.
Keywords: developing countries, hydrological models, operational hydrology, regionalization