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Evapotranspiration Data

Data are available as tab delimited files

Download data summary and data files for Everglades Et sites, 1996-2003 as one zipped file (25.5 MB)


A regional evaluation of evapotranspiration (Et) in the Florida Everglades began in 1996 with operation of 9 sites at locations selected to represent the sawgrass or cattail marshes, wet prairie, and open-water areas that constitute most of the natural Everglades system. The Bowen-ratio energy-budget method was used to measure Et at 30-minute intervals. Site models were developed to determine Et for intervals when a Bowen ratio could not be accurately determined. Regional models were then developed for determining 30-minute Et at any location as a function of solar intensity and water depth using data from the 9 sites for 1996-97.

Five of the original 9 sites continued in operation after 1997 for various periods. Two of these sites were operated continuously until September 2003. Three new sites were installed in the western part of Shark Valley in November 2001 for the purpose of testing regional model transferability. Additionally, an evaporation pan was installed at one site in April 2001 for comparing actual Et determined by the Bowen-ratio site with potential pan evaporation. All data collection ended in September 2003.

This document describes the format of data files of meteorological and evapotranspiration data. Additionally, tables listing model coefficients and goodness-of-fit statistics for site models for the period 1998-2003 are included, and tables listing a comparison for measured Et and Et estimated from the regional models.

This latest data release is different in format from the original release for all data from 1998 on. No changes were made in the 1996-97 data.

One change made in reporting format is that Et data from 1998 on are not smoothed by averaging over one or more measurement intervals. Although the Bowen-ratio method provides Et at 30-minute intervals, Et totals were previously (1996-97) smoothed by computing sums for 60-minute intervals at vegetated sites, and 180-minute intervals at open-water sites. This smoothing helps to remove "noise" from the Et data caused chiefly by imprecision in the determination of water heat storage and/or Bowen ratio during some measurement intervals. This imprecision is likely greater during periods of high water level, when small errors in estimating the temperature of the surface water column account for relatively large parts of the energy budget. Another factor is that the Bowen ratio is difficult to determine accurately during night-time or other periods when temperature and/or vapor pressure gradients are small. Because the Bowen ratio is the quotient of the air temperature and vapor pressure gradients, small errors in determining either of these gradients can cause relatively large variation in the computation of the Bowen ratio.

With this release data are provided at the measurement interval so that users may use whatever smoothing technique that is appropriate for the intended use. It should be emphasized that the 30-minute Et sums may at time indicate short-term variation that is probably not realistic. Averaging over several intervals is likely to produce a more realistic pattern of Et variation. Averaging Et at a daily interval has the advantage of removing most of the uncertainty in the water heat storage term, because water temperatures generally increase during the day and then decrease at night, with little net change in temperature (and water heat storage) for the entire day.

Another change in format for data from 1998 on is that Et sums are provided for "raw" and "edited" 30-minute periods. The "raw" data refer to Et sums that have not been edited from computed results, although the Et sum may be an actual measurement that has passed all input-data screening tests (see WRI 00-4217), or may be a "gap-filled" value computed from the Priestley-Taylor site mode that was developed using only data that passed all screening tests. Data in the "edited" column have been edited graphically by comparing each value to the pattern of Et defined by the entire set of data during part of a day. For example, if a spike in Et at night did not seem to be "real" in relation to available energy measurement and other Et values before and after the spike, the value was adjusted graphically by selecting the plotted value and "dragging" it into line with the pattern defined by the other data. This editing procedure is, of course, subjective, so the raw, unedited data are provided for those who prefer to use unedited data, or to use their own editing technique, such as data averaging or some other form of smoothing.

The final change in format for data from 1998 on is that a flag indicator is provided to show which 30-minute Et data are measured and which are model derived because the input data did not pass screening criteria.

Details concerning data collection, Et computation, and site information are given in:

German, E.R., 2000, Regional evaluation of evapotranspiration in the Everglades:
U.S. Geological Survey Investigations Report 00-4217, 48p.

This report can be downloaded from the following internet site:

(Please use the links on the left for additional information pertaining to this data.)

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Last updated: 15 January, 2013 @ 12:42 PM(TJE)