Water and Energy Cycle
The availability of fresh water on planet Earth affects billions of people. Floods and drought can be life-threatening. The following questions guide research within the Water and Energy Cycle Focus Area:
- How are global precipitation, evaporation, and the cycling of water changing?
- What are the effects of clouds and surface hydrologic processes on Earth's climate?
- How are variations in local weather, precipitation and water resources related to global climate variation?
- How will water cycle dynamics change in the future?
As these water and energy cycle questions are addressed, we gain the understanding and observing capabilities to better contend with the hydrologic, water resource, and related weather issues that underlie habitability of the planet.
The Water and Energy Cycle Focus Area studies the distribution, transport, and transformation of water and energy within the Earth system. Since solar energy drives water and energy exchanges, the energy cycle and the water cycle are intimately entwined. Thus, research focuses on the closely linked budgets of energy and moisture. Focus area research is aligned with national and international programs including the Global Energy and Water Cycle Experiment and the water cycle activities of the U.S. Climate Change Science Program.
The overarching, long-term goal of the Water and Energy Cycle Focus Area is to develop capabilities to observe, model, and predict the water and energy cycles, including phenomena at regional scales and extreme events such as drought and floods. This goal requires an accounting of the key reservoirs and fluxes within the global water and energy cycles, including their spatial and temporal variability, through integration of all necessary observations and research tools. Further, this goal requires not only documenting and predicting trends in the rate of the Earth's water and energy cycling, but also changes in the frequency and intensity of related meteorological and hydrologic events.
Chart: The Water and Energy Cycle Roadmap will yield improved overall knowledge of the water cycle and improved predictions of the changing of the water and energy cycles.
The approach to these goals rests on a combination of observations, understanding, modeling, prediction, and decision-support systems presented in the Water and Energy Cycle Roadmap. This integrated approach will yield improved overall knowledge of the water cycle and improved predictions of the changing of the water and energy cycles. Future missions on the roadmap will provide key measurements for this focus area including: soil moisture, ocean water storage and flux, global precipitation, ground-water storage, tropospheric water storage, and atmospheric water and energy storage.
Precipitation has only recently been measured from space by the Tropical Rainfall Measuring Mission. The Global Precipitation Measurement (GPM) mission will extend remote sensing of precipitation globally, allowing estimation of this input term in Earth's water budget. Evaporation cannot be measured directly, but can be estimated using models based on estimates of the amount of radiation absorbed by the land, oceans, and atmosphere and validated using selected satellite measurements including ocean salinity from Aquarius and soil moisture from HYDROS. The Water and Energy Cycle Focus Area concentrates on storage as soil moisture, ground water, surface water, and snow.
Other missions whose primary measurements address the needs of other focus areas will provide inputs on sea ice, atmospheric water content, land use and land cover, and total ocean water content. Simultaneous measurements over a two- to three-year period are critical to balancing the water and energy budgets. Measurements of soil moisture with two- to three-day frequency set the highest required temporal resolution within the budgets.
Algorithms for future sensors that can provide better spatial and temporal resolution and coverage are developed through airborne and in situ campaigns and a robust research and analysis program. In situ measurements are used to validate spaceborne measurements and model results. Future measurements, high-resolution soil moisture measurements on a global scale, surface water in rivers and lakes, and snow water equivalent will require some new technologies to be developed, in larger apertures for both passive and active microwave instruments. Higher resolution soil moisture measurements on a global scale will also require improved downlink capabilities.
Water and energy cycle modeling requires projections of future changes in surface hydrological parameters (soil moisture, runoff, evapotranspiration) due to changes in land use and land cover as well as enhancements to radiative transfer models to support finer details of atmospheric interactions.
Water and energy cycle research activities should augment and help connect the goals of the Weather Focus Area, where fast processes are studied, and the Climate Variability and Change Focus Area, where longer term process are studied. To achieve the desired accuracy in characterizing the water budget requires several key climatic inputs including sea-ice extent, as well as atmospheric water content at all levels. The energy budget requires significant inputs on solar radiation and Earth radiation.
By 2015, research within the Water and Energy Cycle Focus Area is expected to improve intermediate range forecasts for droughts and seasonal water supply and predict global scale energy storage and transport in the atmosphere by meeting two goals:
- Enable seasonal precipitation forecasts with greater than 75% accuracy at 10's of km resolution; and
- Balance global water and energy budgets.