Location
Pick the field on the map or type its coordinates. The location decides which weather and soil data the app can fetch (gridMET covers the contiguous United States; SSURGO soils cover the United States), and latitude and elevation enter the reference ET calculation.
Location: the science
Latitude sets day length and the radiation reaching the top of the atmosphere (FAO-56 1998, Eq. 21). Elevation sets air pressure, which enters the psychrometric constant (Eqs. 7 and 8).
Outside the United States you can still run a simulation by uploading your own weather file and entering soil properties by hand.
The values on this page
- Latitude
-
Site latitude in decimal degrees (north is positive).
Sets day length and extraterrestrial radiation (FAO-56 1998, Eq. 21), which feed the net radiation term of reference evapotranspiration.Source: Allen et al. (1998), FAO-56. Eq. 21
- Longitude
-
Site longitude in decimal degrees (east is positive, so the United States is negative).
Used to locate weather and soil data; it does not enter the daily calculations.
- Elevation
-
Site elevation above sea level.
Sets atmospheric pressure and the psychrometric constant (FAO-56 1998, Eqs. 7 and 8) and clear-sky radiation (Eq. 37) in reference evapotranspiration. An error of a few hundred metres changes ETo only slightly.Source: Allen et al. (1998), FAO-56. Eqs. 7, 8 and 37