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 (click here for a map of the sites, and here 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:
And that meet the following criteria:
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).