
The World Hydrological Cycle Observing System (WHYCOS) aims to strengthen national capacities in basic observation, foster basin-wide, regional and international cooperation and promote the free exchange of hydrological data.
Its ultimate goal is to support decision-making in water management through the provision of reliable data and information. It envisions bolstering sustainable socio-economic development, environmental protection, mitigation and adaptation to climate change effects, and conflict prevention, especially in transboundary catchments.
The programme underwent a full review in 2011 that highlighted the need to enhance the sustainability and effectivity of the projects achievements (both financial and operational). As a response, the WHYCOS programme is now at the core of the newly established Global Hydrometry Support Facility (WMO HydroHub).

The WHYCOS is implemented through regional components called HYCOS projects. Since its formation in 1993, over 14 HYCOSs projects have been undertaken around the world.
HYCOS projects are based on user requirements, and operate in a bottom-up approach - from the country level up through a basin, regional and global scale. They focus primarily on surface water streamflow, but also consider other elements, such as precipitation, groundwater and basic water quality variables.
These projects are implemented independently, and aim to improve the technical and institutional capacities of National Meteorological and Hydrological Services (NMHSs).

Projects
HYCOS projects have been put in place in different regions and basins of the world:
- the Mediterranean (MED-HYCOS)
- Western and Central Africa (AOC-HYCOS, Niger-HYCOS, Volta-HYCOS)
- Eastern Africa (IGAD-HYCOS)
- Southern Africa (SADC-HYCOS)
- the Arctic (Arctic-HYCOS)
- the Caribbean (Carib-HYCOS)
- the Pacific (Pacific-HYCOS)
- South East Asia (Mekong-HYCOS, Hindu Kush Himalayan-HYCOS)
Many other projects are at different stages of development (Senegal, Congo, Indian Ocean, among others). HYCOSs helped in rehabilitating and expanding observation networks to over 500 hydrological stations.
Training materials
Reinforcing staff capabilities and skills is one of the pillar of HYCOS success. Developed during the implementation of HYCOS projects, the training materials can also be used in other contexts and for different purposes. They comprise a variety of resources (manuals, guidelines, presentations) about all aspects of operational hydrology (e.g. topography, stream gauging, basic groundwater, rating curve, water quality monitoring, data management, and teletransmission).
Guidelines
Guidelines have been developed to ensure a common approach to the management of all HYCOS projects, while still responding to specific local needs and changing situations. They provide guidance for the main stages, including initiation, design, implementation and management, as well as monitoring and evaluation.