What is this?

CEOP, the GEWEX Coordinated Enhanced Observing Period, has as its overarching goal "To understand and model the influence of continental hydroclimate processes on the predictability of global atmospheric circulation and changes in water resources ...". The first of two CEOP objectives is "To use enhanced observations to better document and simulate water and energy fluxes and reservoirs over land and diurnal to annual temporal scales and to better predict these on temporal scales up to seasonal for water resource applications." One major element of CEOP is a set of reference sites, which per the Implementation Plan, are to be "Well-instrumented locations of small to intermediate scales area (10,000 km^2 or less) distributed around the globe in different climatic regimes [that] will provide the data needed on a mesoscale or smaller scale for research in land area and hydrology proceses and model validation." To date, about 40 sites have been identified (see www.joss.ucar.edu/ghp/ceopdm/ref_site.html for a map of the sites, and www.joss.ucar.edu/ghp/ceopdm/rsite.html for a summary of their characteristics).

Few of these sites have a surface hydrologic context, however, which for sake of discussion, we define as being the ability to observe directly most of components of the surface water budget (precipitation, streamflow, evapotranspiration, and surface and subsurface storage change). Most of the CEOP reference sites are in fact flux towers, or groups of flux towers, at which precipitation and other surface meteorological variables may also be measured. Very few lie within gaged catchments, hence arguably the most hydrologically important variable is not observed at more than a small handfull of the sites. Clearly, the surface flux information collected at the reference sites is extremely useful for a variety of purposes related to CEOP objectives, but it cannot, at least alone, fulfill the stated purpose of the reference sites related to hydrological processes.

We are attempting to augment the CEOP tower flux sites with a small set of hydrological reference sites that will have the following purposes:

To serve as validation sites for the land surface parameterizations in coupled land-atmosphere-ocean models, essentially at a point or small area scale;
To serve as "tie points" or ground truth reference sites for remote sensing products

And that meet the following criteria:

Stream gauge information should be available for a reference catchment within which the other (e.g., tower) observation sites lie. The catchment drainage area ideally should be in the range 100-1000 km^2, recognizing that for some sites drainage areas as small as 10 km^2 and as large as 10,000 km^2 may be acceptable;
Precipitation data, either from gauges or radar, sufficient to resolve the major modes of spatial variability within the catchment;
Tower flux observations available for at least one site within the catchment, and land cover, soul and other ancillary data sufficient to support flux transfer methods such as those utilized by Betts(?) and Nijssen and Lettenmaier which could provide spatial interpolation of tower evapotranspiration estimates;
Ideally, multiple year time series of the major water and energy balance terms.

Although we expect that in most cases streamflow observations would focus attention on a drainage area, there may be some situations where other observations would meet the requirement. This might be the case, for instance, in areas of very low relief, where drainage catchments are not well defined and hence stream discharge measurments are problematic, but where soil moisture and/or water table measurments could provide direct estimates of storage change.

This web site summarizes some attributes of a set of global sites that have been identified as the candidates for official CEOP hydrology reference sites, and that meet most, if not all, of the above criteria. The sites currently are:

Brief summaries are accessible from this page for each of the sites, as is a data entry from for entering summary information for new sites. For further information, contact Dennis Lettenmaier (University of Washington, dennisl@u.washington.edu) or Eric Wood (Princeton University, efwood@princeton.edu). If you have any problems when using/viewing this page, please email lluo@princeton.edu .