Water Cycles Across Scales

Dr. Roy Rasmussen - Project Lead

WCAS:

Water Cycles Across Scales

While the water cycle is a global problem, increased knowledge over the continental US will lead to significantly better understanding and prediction of key aspects, on scales ranging from storm-scale to climatic fluctuations. This improvement has the potential to dramatically alter the public's ability to plan for and react to significant weather events. We begin this effort by seeking to understand how water vapor, precipitation, and land-surface hydrology interact across scales to define the hydrological cycle up to a continental scale, and thus improve large-scale prediction models. A key area of research will be to better understand and measure the components of the water cycle work together as a coupled system. Our long-term objectives are to:

• Translate our expertise on small-scale processes into effective representations of these processes at large scales;
• Improve our knowledge of the space and time distribution of water vapor across scales and its role in the initiation, growth, and dissipation of cloud and precipitation systems;
• Conduct systematic analyses of precipitation processes with observations and models;
• Improve our basic knowledge and modeling capability of the hydrological cycle, and quantify runoff, soil moisture, and recycling of moisture for various time and space scales;
• Provide a physical basis for the hydrological cycle and associated extremes in precipitation related to droughts and floods and also climate change;
• Improve the treatment of the water cycle in models across scales, from cloud-resolving to global;
• Improve the prediction of the water cycle using expert systems in the 1-12 hr interval, where a critical gap exists between observations and the predictive skill of models.

Methodology

WCAS is focused on how the various components of the water cycle interact over a specific geographical area, rather than on the details of any individual process over different locations. For instance, the formation of a flash flood is due to high volumes of rain falling in a small geographic area over a short period of time. The formation of the rain involves microphysical processes, while the dynamical triggering mechanisms for cloud formation may be due to mesoscale or synoptic forcing on large scales, while the rapid accumulation of water into a flood involves intermediate scales. In addition, interactions between convective scale processes and the local environment, such as between convective outflows and vertical shear, or the atmospheric response to convective heating, can control the evolution and movement of convective systems. Therefore, we adopt a multidisciplinary, multi-scale strategy that straddles four NCAR Divisions ( ATD - CGD - MMM - RAL).