56. PENMAN MONTEIT CALCULATION

Guidelines for the calculation of Reference Crop Evapotranspiration

Penman Monteith Calculation assignment details.

The aim of the assessment is to gain an understanding of the way climate data determine the reference crop evapotranspiration and of the way FAO have implemented the Penman- Monteith equation.

You are required to calculate reference crop evapotranspiration for one month. The calculation should follow the FAO 56 procedure and consists in filling in the blank boxes on the enclosed calculation sheet. In general the original climatic data are on the left of the form and the calculated values towards the right. Note that there is a sequence to the calculations in that boxes you calculate near the beginning are used later in the calculations.

The basis of the procedure is outlined in the document “Calculation of Reference Crop Evapotranspiration”.

Please see the following attached documents to be able complete this task by filling out Document 3-3 (all of the documents named below are attached.

Document 1-1 HARARE’s Monthly mean data for the contrasting station (use the month of January)

Document 2-2 Calculation of Reference Crop Evapotranspiration FAO 56. (use the FAO Penman-Monteith equation. FAO Penman-Monteith equation

From the original Penman-Monteith equation (Equation 3) and the equations of the aerodynamic (Equation 4)

and surface resistance (Equation 5), the FAO Penman-Monteith method to estimate ETo can be derived (Box

6):

Document 3-3 Calculation Sheet for Eto (FAO Penman Monteith) using Meteorological tables of Annex 2-blank sheet

Document 4-4 TABLES 2.1 through 2.8 Atmospheric pressure (P) for different altitudes (z) (to fill out calculation sheet 3-3)

Document 5-5 TABLE 2.6. Daily extraterrestrial radiation (Ra) for different latitudes for the 15th day of the month

Document 6-6 Completed Answer sheet for BANGKOK- Calculation sheet (you can reference to this guide and see how The Bangkok mean Data question was calculated – For guide only

Document 7-7 Bangkok Data – For guide only