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A strategic programme for NERC Lowland catchment research
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New methods to estimate catchment evaporation

Title

New methods to estimate grid or catchment evaporation using satellite and ground based measurements.

Aims

This study tested the hypothesis that: while field scale measurements may be most accurate at the point of measurement, the errors introduced by their extrapolation when looking at the catchment as a whole, outweigh the errors involved in applying remote sensing techniques.

The overall hypothesis is founded on three issues, which must be addressed if we are to claim a complete knowledge and understanding of the hydrology of the LOCAR catchments:

Main findings and outputs

  • There is considerable variability of evaporation across the landscape linked to land cover, soils and meteorology
  • Uncertainties in our estimates of evaporation tend to reduce as we go to catchment averages
  • There is considerable potential for the estimation of catchment average evaporation using available gridded data sets
  • The LOCAR data set is proving extremely powerful - for the first time (in the UK at least) we have simultaneous measurements of soil moisture, evaporation and hydrological measurements
  • successful ground-truthing of satellite-derived net radiation estimates for clear skies has been achieved.

Description of activities

Newly available satellite measurements were combined with conventional and novel surface measurements, using geographical information system (GIS) techniques. An important facet of the study was a thorough analysis of error at every stage that allowed a quantitative assessment of techniques.

Related and future work

Development of a longwave algorithm to estimate the down-welling longwave radiation at the surface is continuing as part of the NERC funded project NE/C52038X/1 which focuses on the impact of Saharan dust aerosol on the surface radiation budget.

Scintillometry work is continuing with the development of a microwave instrument (which measures evaporation directly) under NERC grant number NE/B506143.

Researchers' details

Principal Investigator:

Co-investigators:

Other researchers:

  • Dr E Blyth, Centre for Ecology and Hydrology
  • Dr J Evans, Centre for Ecology and Hydrology
  • Professor J E Harries, Imperial College London

Publications

All publications from this and other LOCAR projects are listed in the publications database.

Refereed journal papers

Bantges, R.J., Harries, J.E., Evans, J.G., Estimates of the total net energy flux at the surface from satellite observations - A case study. In preparation.

Blyth, E.M., Evans, J.G., Finch, J.W., Bantges, R. and, Harding, R.J., 2006. Spatial variability of the English agricultural landscape and its effect on evaporation. Agricultural and Forest Meteorology, 138, 19-28

Conference proceedings

Evans, J.G., Bantges, R ,Finch, J.W., Blyth, E.M., Harding, R.J and Murray,T., 2005 Large Aperture Scintillometry over Complex Terrain:Results from Chalk Down-land. European Meteorological Society Conference 2005.

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