DEFINING WATERSHED‐SCALE EVAPORATION USING A NORMALIZED DIFFERENCE VEGETATION INDEX¹

Abstract

Monthly composites of the Normalized Difference Vegetation Indices (NDVI), derived from the National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVILRR), were transformed linearly into monthly evaporation rates and compared with detailed hydrologic‐model simulation results for five watersheds across the United States. Model‐simulated monthly evaporation values showed high correlations (mean R2= .77) with NDVI‐derived evaporation estimates. These latter estimates, used in a classical water balance model, resulted in equally accurate simulations of monthly runoff than when the model was run to estimate monthly evaporation via soil moisture accounting. Comparison of NDVI‐derived evaporation estimates with pan data showed promise for transforming NDVI values into evaporation estimates under both wet and water‐limiting conditions without resorting to the application of any kind of calibrated hydrologic models.

PRIESTLEY‐TAYLOR ALPHA COEFFICIENT: VARIABILITY AND RELATIONSHIP TO NDVI IN ARCTIC TUNDRA LANDSCAPES1

“…In order to estimate α at these spatial scales while accounting for seasonal changes described in previous studies (i.e., 15-days) (Rovanesk et al, 1996) the only suitable satellite data available at the time were from the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) suite of satellites. Therefore, NDVI values were extracted from the NOAA AVHRR maximum value composite (MVC) images that have been used as a data input in a number of other ET studies (e.g., Szilagyi and Parlange, 1999). The MVC NDVI images are twice monthly or biweekly (depending on the year) composites of the highest NDVI values, derived on a pixel-by-pixel basis and extracted from a georeferenced, multitemporal data set (Holben, 1986).…”

Vegetation Indices to Aid Areal Evapotranspiration Estimations

“…With the emer-gence of space technology, satellite-derived vegetation indices, such as the Normalized Difference Vegetation Index (NDVI ϭ͓NIR-R͔/͓NIRϩR͔, where NIR and R are the spectral responses of the vegetated surface at the near-infrared and red bands, respectively͒, have become essential for gathering biophysical information on the vegetation status of large, arbitrarily defined regions. Since the vegetation status ͑e.g., greenness͒ integrates the effects of numerous environmental factors, these indices can be correlated with different hydrological variables, such as AET ͑Seevers and Ottmann 1994; Nicholson et al 1996;Szilagyi et al 1998;Szilagyi and Parlange 1999;Szilagyi 2000͒. Different authors drew differing conclusions about the applicability of NDVI to estimate AET. For example, Seevers andOttmann ͑1994͒ andNicholson et al ͑1996͒ pointed out that the NDVI-AET relationship is strong mainly in humid environments.…”

Evaporation from cultivated and semi-wild Sudanian Savanna in west Africa

“…The partition of net radiation into sensible heat, evaporation, and soil heat flux drives global atmospheric processes and is controlled by interacting surface and atmospheric conditions (Foken, 2008;Szilagyi and Parlange, 1999).…”

“…The evaporative fraction, the ratio of latent heat flux to available energy, is useful to estimate total daily evaporation with measurements of a single component of the energy balance and to upscale surface measurements using remote sensing products (Brutsaert and Sugita, 1992;Compaore, 2006;Porte-Agel et al, 2000;Shuttleworth et al, 1989;Szilagyi et al, 1998;Szilagyi and Parlange, 1999). Using evaporative fraction to calculate the total daily evaporation is based on the concept of self-preservation in the diurnal evolution of the surface energy budget (Brutsaert and Sugita, 1992;PorteAgel et al, 2000), stating that the diurnal cycle of each of the energetic fluxes will resemble that of available energy, even if there is variation in the quantity, allowing for exploiting satellite data that are typically only obtainable once a day at best.…”