These are explained below. In each case, the minimum data required are believed to be readily available for the basins to be used. The desired level of data are also believed to be available in many basins.

Basic Required Observations for Development and Testing

Historical/retrospective data are needed for many years (as long as possible; e.g. in the U.S. the period 1948-date) at around 200 test basins which have the minimum observations and basin physical characteristics data and which cover a wide range of climate, soils and vegetation characteristics. (Where available, basins which have the additional data discussed in the following section will be selected to cover the range of characteristics.) The main types of required historical data are: hourly and daily gaged precipitation; daily maximum, minimum and average temperature; surface meteorological observations and daily average stream discharges. These minimum data requirements for MOPEX are actually quite modest, although a higher level of data would be desirable. Since the desirable level of data are unachievable for all basins, the most important requirement is the minimum level. The data requirements are summarized in Table 1.   Table 2 lists the minumum number of raingages desired for basins of given size (see Schaake, 1981).

The most basic minimum requirement is to have daily precipitation and streamflow with climatological monthly mean statistics of the following surface meteorological variables air temperature, relative humidity, wind speed and cloud cover. The surface observation statistics would be used to estimate potential evaporation for some schemes and radiative forcing for others. Experience in hydrological modelling is that good parameter estimates can be made with climatological statistics to estimate energy forcing.

TABLE 1 SUMMARY OF MINIMUM BASIN REQUIRED OBSERVATIONS

Description Requirement	Minimum	Desired
Precipitation	Daily	Hourly
Streamflow	Daily	Hourly
Surface Meteorology observations	Monthly statistics	Daily/Hourly

TABLE 2 DESIRED MINIMUM NUMBER OF RAINGAGES PER BASIN

 

Required Physical Characteristics

Supporting basin boundary, stream and land characteristics data relating to topography, soils and vegetation are also needed (Table 3). Some of these supporting data are already available on the ISLSCP CD-ROM, but additional data and refinement of the ISLSCP data to a scale greater than 0.5⁰ are required.

TABLE 3 REQUIRED BASIN PHYSICAL CHARACTERISTICS

Description Requirement	Minimum	Desired
Elevation	5 km/5 m contours	1 km/1 m
Basin Boundaries	10 km/Location	1 km
Streams	10 km/Location	1 km
Soils - texture, hydraulic properties, etc	20 km	1 km
Vegetation - type, rooting depth, phenology, etc	20 km/Monthly	1 km/Weekly
Geology	10 km	1 km

Desirable Additional Observations

Having actual measurements of meteorological surface variables at daily or hourly steps will improve the simulations of land surface schemes. If diurnal fluctuations of surface fluxes are to be simulated detailed measurements of energy forcing variables are needed. These data are not critical to estimate those parameters that can be extracted from long periods of precipitation and runoff, although they might contribute to the development of improved parameter estimation techniques and to testing the techniques developed only with the minimum required data. Daily or hourly meteorological surface observations are expected to be available for at least half of the 200 basins.

Table 4 lists the desired additional observations.

TABLE 4    SUMMARY OF DESIRED ADDITIONAL OBSERVATIONS

Description Requirement	Minimum	Desired
Snow Cover - satellite product	Seasonal statistics	Daily/1 km
Snow Water Equivalent	Seasonal statistics	Daily
Pan Evaporation	Seasonal statistics	Daily
Clouds	Daily1	3-hourly
Short Wave Radiation	Daily2	Hourly
Long Wave Radiation	Daily3	Hourly
Soil Moisture	Weekly	Daily

Notes:

¹ Cloud cover is required to estimate solar radiation.

² Short wave radiation may not be available except from satellite estimates.

³ Long wave radiation is unlikely to be available and can be estimated from surface observations.

Observations for Detailed Testing and Evaluation.

The observations for detailed testing and evaluation will make use of the enhanced observations of the detailed research areas of the CSEs. The data expected to be available would include all of the above as well as flux measurements, soil temperature and moisture profiles, etc. In addition to a higher density of point observations areal estimates of these and remote sensing data would be available from the CSEs to examine some of the scaling issues associated with land surface models.

Data Available

Data have been assembled from US basins and from international basins. Hydrometeorological data for 438 US basins are now available. Corresponding basin characteristics data have also been collected. The retrospective hydrometeorological data include hourly precipitation data and hourly meteorological forcing data for period from 1960 to 1998. The meteorological forcing data are dervied the data sets developed by Dennis Lettenmaier's group at the University of Washington (http://www.hydro.washington.edu/Lettenmaier/gridded_data/)*. Daily streamflow data are available for the same period (derived from USGS data http://www.nwis.usgs.gov). Other data include climate potential evapotranspiration (PET) based on NOAA Pan Evaporation Atlas. Twelve of the 438 basins are selected for the second and third MOPEX workshops, held respectively in April 2002 in Tucson, AZ and in July 2003 in Sapporo, Japan.

Data from other countries, including UK, France, Germany, and Australia, among others, are also obtained. Data from additional US basins and from international basins will be used for the future MOPEX workshops to be held in July 2004 in Paris, France and In April 2005 in Brazil.

Data Dissemination

MOPEX data sets are available via anonymous ftp at:

ftp://hydrology.nws.noaa.gov/pub/gcip/mopex/US_Data/

For inquiries, send email to <John.Schaake@noaa.gov>

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