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.

Links to Other Programs

GEWEX is the core project in WCRP concerned with studying the dynamics and thermodynamics of the atmosphere and interactions with the Earth's surface. 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.  These linkages are expected to increase in response to the recent WCRP strategy for international research and collaboration, the Coordinated Observation and Prediction of the Earth System.

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.

Research Foci

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

• Radiation - Determine atmospheric and surface radiation fluxes and heating with the precision needed to predict transient climate variations and decadal-to-centennial climate trends.
• Hydroclimate - Demonstrate 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.
• Modelling and Prediction - Develop accurate global model formulation of the energy and water budget and demonstrate predictability of their variability and response to climate forcing.

GEWEX -- A Phased Project

From the beginning, GEWEX has been a phased project, initially conceived to take advantage of the development of the new series of environmental satellites (e.g., TERRA, AQUA, TRMM, ENVISAT, ADEOS I and II). Phase I (1990-2002) was designed as a buildup phase maximizing the climate use of the current operational and research satellite data prior to the new satellites. Phase II (2003-2012) is designed to begin the scientific exploitation of the data from the new satellite sensors. See Water and Energy Cycles:  Investigating the Links, for a brief overview of the GEWEX Program and its two phases.

Phase I Objectives

• 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 assimiliation systems for operational application to long-range weather forecasts, hydrology, and climate predictions.

Phase I Results

Phase I of GEWEX has shown the usefulness and critical value of satellite data in addressing vital Intergovernmental Panel on Climate Change (IPCC) questions. International Satellite Cloud Climatology Project (ISCCP) data have, for the first time, have been able to show a global impact and view of the indirect aerosol effect (on clouds) a special concern of the IPCC.   Also, the use of the Global Precipitation Climatology Project (GPCP) and Global Water Vapor Project (GVaP) data sets have been able to begin addressing the atmospheric residence time of water vapor and the key IPCC questions regarding the acceleration of the global hydrologic cycle.

GEWEX has been able to show the linkage between the local process, global model predictions, and the downscaling to the local scale necessary to determine the impacts on local water resources and society. This process also emphasizes the need for satellite 4DDA, as well as the implementation of the new ensemble prediction approach in linking to the water resource applications activities.

The GEWEX emphasis on improved coupled land-surface and atmosphere representations in prediction models at all scales has illustrated the direct links to the water cycle and has provided increased importance of both existing and future satellite sensing of the land and near surface parameters. This is leading the way for greater direct use of satellite sensed skin temperature, surface vegetation characteristics, snow, soil moisture, etc., as well as the atmospheric profiling requirements.

Phase I Results Summarized

• 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.

GEWEX Accomplishments - Phase I

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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.

Phase II

GEWEX is in Phase II (2003-2012), which in the context of the original objectives, is addressing the following principal scientific questions.

• Are the Earth's energy budget and water cycle changing?
• How do processes contribute to feedback and causes of natural variability?
• Can we predict these changes on up to seasonal to interannual?
• What are the impacts of these changes on water resources?

In Phase II  there will also be increasing interaction with the water resource and applications communities to ensure the usefulness of GEWEX results.  This will require the development and use of a wide range of modeling tools ranging from the full global climate models to regional and mesoscale models, and to downscaling methods suitable for the smaller spatial and temporal scales generally associated with hydrological models used in local water resource management.

Phase II Objectives

• 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.