CREW's mission is to quantify and predict water cycle and environmental consequences of earth system variability and change through focused research investments in observation, modeling, and application.
Earth is a unique, living planet due to the abundance and vigorous cycling and replenishing of water throughout the global environment. The water cycle operates on a continuum of time and space scales and exchanges large amounts of energy as water undergoes phase changes and is moved from one part of the Earth system to another. Water is essential to life and is central to society’s welfare, progress, and sustainable economic growth. However, global water cycle variability which regulates flood, drought, and disease hazards is being continuously transformed by climate change, erosion, pollution, salinization, and agriculture and civil engineering practices. The water cycle delivers the consequences of climate change. In fact, Asrar et al., 2001 states that “ the most significant manifestation of climate change for humans and the environment is an intensification of the global water cycle, leading to increased global precipitation, faster evaporation, and a general exacerbation of extreme hydrologic regimes, floods, and droughts”. And the U.S. National Research Council report Research Pathways for the Next Decade recognized that “Water is at the heart of both the causes and the effects of climate change. It is essential to establish current rates of, and possible changes in precipitation, evapotranspiration, and cloud water content” (NRC, 1999). An intensified water and energy cycle would be expected to produce more frequent or severe weather disturbances. We have observed a significant global mean temperature increase over the last 20 years (Bengtsson et al. 1999), and United States precipitation has increased by about 10% during the last century, with much of the change resulting from heavy rainfall frequency and intensity increases (Morel, 2001).The most visible manifestation that could be expected from climate warming would be changes in the distribution of precipitation and evaporation, and the exacerbation of extreme hydrologic events, floods and droughts. From both scientific and practical perspectives, the key question is whether projected climate change will entail significant changes in the Earth’s global water cycle. Beyond the traditional goal of climate research to predict expected changes in the equilibrium state of the climate system, CREW aims to quantify and predict the energy sources and sinks that feed baroclinic weather systems, the general circulation of the atmosphere, global water transport, rainfall, and the renewal of fresh water resources. There are three distinct reasons to quantify and predict the global water cycle:
1. Water vapor is by far the largest and most variable contributor to the global greenhouse effect. In fact, uncertainty caused by natural variability in infrared absorption by atmospheric water vapor and measurement or modeling errors dwarf any uncertainty associated with projected concentrations of all other (largely passive) greenhouse gases. For this reason, developing physics-based predictions of atmospheric water vapor distribution under modified climate regimes is a crucial requirement for reducing the uncertainty of model simulated climate change projections.
2. Latent heat fluxes associated with water vapor transport, precipitation and evaporation are the principal mode of energy exchange between the Earth surface and the atmosphere, as well as the main driver of weather processes. Since weather is part of climate, quantifying the energy fluxes associated with water cycling at the Earth surface and in the troposphere should be a core objective of modern climate research.
3. Constant renewal of fresh water reserves is a crucial condition for the existence of life on Earth as well as agricultural and industrial activities of major economic importance. Global evaporation, atmospheric transport and precipitation are the processes that control the renewal of fresh water resources. Quantifying these processes is a prerequisite for extending the applications of hydrologic sciences into the future when information based on past climate statistics could not be relied upon any more.
The Center: CREW integrates research across traditional disciplines in an end-to-end program that transitions theoretical research to academic/public education and real-world application, through partnerships with universities, government, and international agencies. The center goal of improved and applicable predictions of the water and energy cycles will require decisive progression from observations to improved understanding and modeling, and eventually to better prediction and application. The center can not possibly hope to achieve this objective alone, but rather conducts focused activities aimed at improving existing partner capabilities. For example, among others, the Land Data Assimilation System (LDAS) is a core center focus that enables partner capabilities through focused research on data assimilation and initialization. To focus CREW on making decisive progress toward quantifying and predicting water cycle and environmental consequences of earth system variability and change, we adopt three central CREW elements: (1) Observation, (2) Modeling & Prediction, and (3) Solutions. We establish a progressive path from deriving knowledge from water and energy cycle observations that can be transitioned into useful prediction skill, and demonstrated in practical end-use solutions. The three CREW elements can be summarized as follows:
Observation: Quantify long-term water cycle trends & variability; enable progression toward a coordinated water cycle observation system; extract knowledge and understanding from diverse observations to enhance prediction capability.
Modeling & Prediction: Use multiple state-of-the-art, operational, earth-system models; conduct sensitivity and predictability experiments; infuse process-scale understanding to predict water cycle extremes. Enhance prediction through observational constraints; explore limits of water cycle predictability.
Solutions: Enhance operational decision support tools with improved prediction; Engage in public and research community education; application; link to other earth system components.
References:
Asrar, G.; Kaye, J.A.; Morel, P., 2001.NASA research strategy for earth system science: climate component, Bull. Am. Meteorol. Soc., pp. 1309-1329
Bengtsson, L., E. Roeckner and M. Stendel, 1999. Why is global warming
proceeding much slower than expected?, J. Geophys., Res., 104, 3865-3876.
Morel, P., 2001. Why GEWEX? The agenda for a
global energy and water cycle program, GEWEX News, Vol. 11, No.1, WCRP.
NRC, 1999. Global change research pathways for the next decade, Committee on Global Change Research, National Research Council, National Academy Press,
