PROGRAM TITLE:  	Scale Effects of Hydrological Processes
ACTIVITY STREAM: 	Understanding
SCIENCE ELEMENTS:  	Climate and Hydrologic Systems

 U.S. DEPARTMENT OF AGRICULTURE
Agricultural Research Service

SCIENTIFIC MERIT:  Research addresses the critical problem of scale in 
modeling terrestrial hydrologic and atmospheric processes and their 
interactions at point, watershed, and regional scales 
(1 square m to 1000 square km) as well as at the mesoscale (greater than 1000 
square km).  Research includes field experimentation and data collection 
using existing ARS research watersheds, remote sensing and GIS techniques, 
water and energy balance models that are merged with mesoscale 
meteorological models and current and future EOS remotely sensed data.  
Identification of water and energy flux controls on watershed processes at 
different scales  provides information on the relative importance of model 
process components at each scale.  The resulting improvement in 
understanding of linkages and interactions at different scales permits 
quantitative assessment of the effects of global change on the hydrologic 
system and the effects of terrestrial hydrology on the global environment.  
Research results from this program are applicable to TERRA (Which is 
described in greater detail in the USDA/ARS program on Ecosystem 
Modeling.

The Agricultural Research Service (ARS) has carried out a large number of 
plot and field scale and small watershed experiments over the past 30 years to 
estimate water and energy fluxes as functions of vegetation cover and soil 
water status.  Similar information is available for range and timbered sites 
from USGS, FS, and BLM.  The time is right to launch a concerted effort to 
aggregate these fluxes over regional and even mesoscale areas.  A 
considerable volume of pertinent data exists, but a few largeŠscale field 
experiments may be necessary to simultaneously collect measurements of 
water and energy fluxes from hierarchical nests of stations over GCM 
subgrids.  ARS hydrologists are closely linked to a global network of other 
hydrologic scientists dealing with these issues, and are providing important 
leadership to major hydrologic modeling efforts.

STAKEHOLDERS:   The research benefits all of society through application of 
research results to insure food and fiber production for the Nation on a 
sustainable basis.

POLICY RELEVANCE:  This research is linked with USDA agencies (FS, 
CSRS, and SCS) and with other CEES agencies as opportunities present 
themselves.  Benefits will primarily be scientific information on which to 
develop policies and aid decision making at local, regional, and national 
scales involving the impact of climate and global change on the sustainability 
of food and fiber supplies and the health of the natural resource base.

PROGRAM CONTACT:  R. Dennis Child    Phone (301)  504-5618     FAX   
(301) 504-6231