Estimation of reference evapotranspiration and crop water use in the Arabian peninsula

Abstract EN

The present study aims principally at estimating reference evapotranspiration as well as crop water use in the Arabian Peninsula.

In order to combine the results obtained from this work with the results obtained from earlier studies in Saudi Arabia, some of the procedures that were applied then have been worked out here.

The four procedures we used for estimating the grass reference evapotranspiration were the FAO-Blaney-Criddle, Hargreaves, FAO-Penman, and FAO-Penman-Monteith methods.

The Jensen-Haise and the Jensen procedures were the only two methods used for estimating the alfalfa reference evapotranspiration.

The results obtained show clearly that the estimates obtained by the FAO-Blaney-Criddle and the FAO-Penman methods are generally 10% larger than the grass evapotranspiration given by the FAO-Penman-Monteith method.

Conversely, the Hargreaves estimates are on the average about 6% less than the Penman-Monteith estimates.

The old model of Jensen-Haise gives an average alfalfa reference evapotranspiration almost 15% larger than the grass reference evapotranspiration by Penman-Monteith, whereas the later model by Jensen gives an average difference of about 23%, but for a number of stations only and not for all of them.

The present study shows also that the results obtained from the old and more recent models, both belonging to one method of estimation, are strongly correlated.

This makes it possible to transform the old estimates, if any, to the newer ones without the need to redo the calculations.

The paper also reviews the procedure for estimating crop water use based on the already obtained estimates of either grass or alfalfa reference evapotranspiration.

Since the necessary conversion coefficients are not yet available for the Arabian Peninsula, there is no choice other than using coefficients derived in areas with climatic conditions as near as possible to those in the Peninsula.

An example for estimating the evapotranspiration requirement of sorghum in Qatar is worked out.