Evaporation Measurement Exercise

Evaporation measured by pans will not always reflect actual evaporation.  Actual evaporation is measured by an Energy Balance with Bowen Ratio method or Eddy Covariance method.  Pan evaporation is still used as a surrogate.  To see how these measurements can differ, you can plot the two methods versus time and see how they differ.

Actual evaporation is available from the Atmospheric Radiation Measurement experiment from the US Department of Energy: https://www.arm.gov.

Pan evaporation can be found for sites throughout the country from the National Climatic Data Center: https://www.ncdc.noaa.gov.

You may also be interested in two articles that discuss the differences between evaporation measurements:

Kahler, D. M., and W. Brutsaert (2006), Complementary relationship between daily evaporation in the environment and pan evaporation, Water Resour. Res., 42, W05413, doi:10.1029/2005WR004541.

Hobbins, M. T., J. A. Ramírez, and T. C. Brown (2004), Trends in pan evaporation and actual evapotranspiration across the conterminous U.S.: Paradoxical or complementary? Geophys. Res. Lett., 31, L13503, doi:10.1029/2004GL019846.

Evaporation measurements by pan (pink circles) and EBBR or ECOR (blue triangles) versus aridity index as defined in Kahler and Brutsaert (2006).

If the ARM data archive is having problems, you can download the EBBR data for Cement, OK (data are in W m^{-2}).  The data are provided purely as a convinience and no guarantees on quality are made.  The data are the product of ARM and DoE.  If the NCDC data archive is having problems, you can download the pan evaporation data for Chickasha, OK (data are in hundredths of inches).  The data are provided purely as a convenience and no guarantees on quality are made.  The data are the product of the NCDC and NOAA.