Mission: To observe, understand and model the hydrological cycle and energy fluxes in the Earth's atmosphere and at the surface.

The Global Energy and Water Cycle Exchanges Project (GEWEX) is an integrated program of research, observations, and science activities that focuses on the atmospheric, terestrial, radiative, hydrological, coupled processes, and interactions that determine the global and regional hydrological cycle, radiation and energy transitions, and their involvement in climate change. The International GEWEX Project Office (IGPO) is the focal point for the planning and implementation of all GEWEX activities.

The goal of GEWEX is to reproduce and predict, by means of suitable models, the variations of the global hydrological regime, its impact on atmospheric and surface dynamics, and variations in regional hydrological processes and water resources and their response to changes in the environment, such as the increase in greenhouse gases. GEWEX will provide an order of magnitude improvement in the ability to model global precipitation and evaporation, as well as accurate assessment of the sensitivity of atmospheric radiation and clouds to climate change.

GEWEX is the core project in the World Climate Research Programme (WCRP) concerned with studying the dynamics and thermodynamics of the atmosphere, its interactions with the Earth's surface, and the effects on the global energy and water cycle.

By virtue of this central role, GEWEX has links with all other WCRP projects, in particular, the Climate Variability and Predictablity (CLIVAR) Project, the Stratospheric Processes and their Role in Climate (SPARC) Project, and the Climate and Cryosphere (CIiC) Project.  

GEWEX plays a central role in the interaction of WCRP with many international organizations and programs dealing with climate observations. As part of WCRP's input to the Group on Earth Observations (GEO) Global Earth Observation System of Systems (GEOSS), GEWEX brings its unique expertise in two specific societal benefit areas, climate and water. GEWEX is leading in the development of plans for the global data reprocessing effort and a observation strategy, and serves as a demonstration project for future climate observational networks in GEOSS. GEWEX supports the Integrated Global Water Cycle Observations (IGWCO) Theme developed under the Integrated Global Observing Strategy Partnership (IGOS-P) and currently part of GEO (activities were merged in 2008).

GEWEX also maintains close links to the International Land Ecosystem-Atmospheric Processes Study (iLEAPs) of the International Geosphere-Biosphere Program (IGBP). 

GEWEX is composed of several components designed to address the elements of the scientific focus, the global energy and water cycle.

• Data and Assessment - Determine atmospheric and surface radiation fluxes and heating with the precision needed to predict transient climate variations and decadal-to-centennial climate trends.
• Hydroclimatology - Demonstrate - in particular at the regional scale - skill in predicting changes in water resources and soil moisture on time scales up to seasonal and annual as an integral part of the climate system.
• Modeling and Prediction - Develop accurate global model formulation of the energy and water budget and demonstrate predictability of their variability and response to climate forcing. See the Global Atmospheric System Studies (GASS) Panel and the Global Land/Atmosphere System Study (GLASS) Panel.

GEWEX Cross-Cutting Themes:

In the implementation of GEWEX, priority continues to be given to three main cross-cutting themes:

1. Assembly of global climatological data sets based on merging in situ measurement and satellite observations in order to determine the atmospheric and surface fluxes that drive the climate system, to provide benchmark values for the present climate, to document interannual variability and climate change, and to validate models.
2. Atmospheric and land surface process studies to improve understanding of the main thermodynamic forces driving the climate system of energy exchanges in the atmosphere, characterizing the regional global and water energy budgets, to evaluate the role of evaporation and precipitation processes in regional rainfall anomalies, to examine changes in soil moisture and ground water balance, and to improve paramertization of these processes in models.
3. Application of GEWEX data and process studies in models as a basis for developing extended range precipitation forecasts, studying water resource variability, improving the realism of simulations of the climate response to anthropogenic forcing and global warming assessments, and for providing input to other WCRP activities.