Phases of GEWEX

GEWEX’s history is marked by three past 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 5 to 10 years and which contribute directly to these.

The current Phase IV (2022-2032) focuses around three overarching goals. In recognition of the emerging challenges in understanding how the water cycle is changing in response to different pressures, and in an attempt to make progress in addressing the issues central to them, GEWEX formulated three science goals with each specific topics of special interest. The full document describing the GEWEX Science Plan for 2022 – 2032 can be found here.

Each phase of GEWEX is described more fully below.

Phase IV: 2022-2032

Phase IV of GEWEX is an extension of the work done within the GEWEX community over the last 30 years where a strong refocus is on process observations, understanding and modeling and where significantly more attention is given to the non-geophysical aspects of the Earth’s system. A summary overview is given below a more extensive treatment can be found in the GEWEX Science Plan 2022-2032.

Goal # 1: Determine the extent to which Earth’s water cycle can be predicted.
This Goal is framed around making quantitative progress on three related areas posed in terms of the following questions:

1. Reservoirs
What is the rate of expansion of the fast reservoirs (atmosphere and land surfaces), what is its spatial character, what factors determine this and to what extent are these changes predictable?

2. Flux exchanges
To what extent are the fluxes of water between Earth’s main reservoirs changing and can these changes be predicted and if so on what time/space scale?

3. Precipitation Extremes
How will local rainfall and its extremes change under climate change across the regions of the world?

Goal # 2: Quantify the inter-relationships between Earth’s energy, water and carbon cycles to advance our understanding of the system and our ability to predict it across scales:

1. Forcing-feedback understanding
How can we improve the understanding of climate forcings and feedbacks formed by energy, water and carbon exchanges?

2. ABL process representation
To what extent are the properties of the atmospheric boundary layer (ABL) defined by sensible and latent energy and water exchanges at the Earth’s surface versus within the atmosphere (i.e., horizontal advection and ABL-free atmosphere exchanges)?

3. Understanding Circulation controls
To what extent are exchanges between water, energy and carbon determined by the large-scale circulations of the atmosphere and oceans?

4. Land-atmosphere interactions
How can we improve the understanding of the role of land surface-atmospheric interactions in the water, energy and carbon budgets across spatiotemporal scales?

Goal # 3: Quantify anthropogenic influences on the water cycle and our ability to understand and predict changes to Earth’s water cycle.

1. Anthropogenic forcing of continental scale water availability
To what extent has the changing greenhouse effect modified the water cycle over different regions and continents?

2. Water management influences
To what extent do water management practices and land use change (e.g., deforestation) modify the water cycle on regional to global scales?

3. Variability and trends of water availability
How do water & land use and climate change affect the variability (including extremes) of the regional and continental water cycle?

Phase III: 2013-2022

Phase III built on the results and experiences from the Phases I and II. The GEWEX Science Questions (GSQs) 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. The GSQs are outlined below; the full text can be found here.

  1. Observations and Predictions of Precipitation: How can we better understand and predict precipitation variability and changes?
  2. Global Water Resource Systems: How do changes in land surface and hydrology influence past and future changes in water availability and security?
  3. Changes in Extremes: How does a warming world affect climate extremes, esp. droughts, floods, and heat waves, and how do land area processes, in particular, contribute?
  4. Water and Energy Cycles and Processes: How can understanding of the effects and uncertainties of water and energy exchanges in the current and changing climate be improved and conveyed?

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 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.