Phases of GEWEX

GEWEX’s history is marked by three phases. Initially, GEWEX was created to take advantage of the new Earth observational satellites being developed in the 1980s. Phase I (1990-2002) of GEWEX focused on the developing analysis tools and models, using operational and research satellites, regional analyses of continental scale basins, and process studies to support the development of parameterizations of feedback processes (relating to clouds and land) for global climate models. The scientific exploitation of the data from the new satellite sensors began in Phase II (2003-2012).

There are a number of evolutionary changes that have occurred within GEWEX that have set the stage for Phase III (2013-2022). Building upon the results and experience from Phases I and II, new GEWEX Vision and Mission Statements were developed, and an Imperatives document that provides the activities necessary to accomplish these was created. In response to the WCRP Grand Challenges, GEWEX also developed four Science Questions to be addressed in the next 5 to 10 years and which contribute directly these. Each phase of GEWEX is described more fully below.

Phase I: 1990-2002


  • Determine the hydrological cycle and energy fluxes by means of global measurements of atmospheric and surface properties.
  • Model the global hydrological cycle and its impact on the atmosphere, oceans and land surfaces.
  • Develop the ability to predict the variations of global and regional hydrological processes and water resources, and their response to environmental change.
  • Advance the development of observing techniques, data management, and assimilation systems for operational application to long-range weather forecasts, hydrology, and climate predictions.


  • 10-25 year global data sets of clouds, precipitation, water vapor, surface radiation, and aerosols–indicating no large global trends, but with evidence of regional variability.
  • Implementation of the land surface and cloud parameterization upgrades suggested for most regional and global models–showing improved precipitation.
  • Initial results from the GEWEX Continental-Scale Experiments–approaching closure of the regional water and energy budgets and determining the importance of recycling and diurnal processes for regional predictions.

A comprehensive summary of Phase 1 is available as GEWEX Accomplishments – Phase I.

Phase II: 2003-2012


  • Produce consistent research quality data sets complete with error descriptions of the Earth’s energy budget and water cycle and their variability and trends on interannual to decadal time scales, and for use in climate system analysis and model development and validation
  • Enhance the understanding of how energy and water cycle processes function and quantify their contribution to climate feedbacks
  • Determine the geographical and seasonal characteristics of the predictability of key water and energy cycle variables over land areas and through collaborations with the wider WCRP community determine the predictability of energy and water cycles on a global basis.
  • Develop better seasonal predictions of water and energy cycle variability through improved parameterizations encapsulating hydrometeorological processes and feedbacks for atmospheric circulation models
  • Undertake joint activities with operational hydrometeorological services and hydrological research programs to demonstrate the value of new GEWEX prediction capabilities, data sets and tools for assessing the consequences of global change.

For an overview of Phase I and II, see Water and Energy Cycles: Investigating the Links, published in the WMO Bulletin, April 2005.

Phase III: 2013-2022

Phase III, currently ongoing, builds on the results and experiences from the Phases I and II. The GEWEX Science Questions provide a near-term framework for the program for the next 5-10 years, and the GEWEX Imperatives provide a longer-ranging framework for the program’s future.