New Mexico State University
Potential and Actual Crop Evapotranspiration Wizard
Using Samani's Equation with Output Formatted for Peman Excel Irrigation Spreedsheet
This system calculates the Potential Evapotranspiration for a given set of data for a given latitude. This page is a compilation of several databases, some global some local to NM, and is fairly involved... not complicated. So if you are new to this system please read the instructions fully.
Step 1: Getting daily weather data: Data can be acquired from the following places or you can enter the data by hand into the Wizard. The data needed is Date, maximum & minimum temperature, and precipitation (optional). NOTE: Do not paste raw data from Excel into this wizard. Formatting issues will prevent this tool from converting the data properly. Please use a plain text editor (e.g. Notepad) as a source of pasted raw data.
Getting the latitude
1. The latitude for the site location must be acquired from the internet site having the maximum and minimum temperature.
2. For the NOAA stations latitude can be acquired from this document,
Note: Value is given as a 4 digit number, i.e. 3241, type this in the box below with a colon ':' between the first two and last two digits,
3. Now you have all the information that this equation requires! Click here to finish.
Notes on kt coefficient:
Reference: Z. A. Samani and M.Pessarakli, 1986: Estimating Potential Crop
Evapotranspiration with Minimum Data in Arizona,
Transactions of the ASAE Vol. 29, No. 2, pp. 522-524
Figure 1 give a comparison between Samani method of calculating Pet and Penman's method for Las Cruces NM
Copyright © 2011 New Mexico State University
Last Updated: October 3 2011
Department of Plant and Environmental Sciences
Box 30003 MSC 3Q
Las Cruces, N M 88003-8003