A SIMPLE PRACTICAL EVAPORIMETER - COMPARISON OF ANDERSSON EVAPORIMETER WITH CLASS-A PAN, PICHE ATMOMETER, AND PENMAN EVAPORATION

A simple but effective evaporimeter, developed by Andersson (1969) but which has not received wide international attention, was compared wit h regard to evaporation with the standard methods Class A pan, Piche a tmometer, and Penman calculation. The Andersson evaporimeter, made of Plexiglas, consists of a lidded cylindrical water reservoir of 0.15 L and can be placed on a pole in the terrain at chosen heights above gro und level. Evaporation takes place through circular holes in the upper part of the reservoir. The reading is performed to an accuracy of 0.0 1 mm. Measurements were made at two meteorological stations in differe nt climate zones. Sidi Bouzid in Tunisia in an arid climate and Kulums a in Ethiopia in a dry subhumid climate. Each site covered 2 year of d aily recordings. At Sidi Bouzid a 1:1 linens relationship was found be tween the Andersson evaporimeter and the Class A pan, whereas at Kulum sa a 0.8:1 relationship was obtained. Furthermore, 1:1 relationships w ere found at both sites between the Andersson evaporimeter and the Pen man calculated values, when the latter were corrected to cope with hea t exchange between device wall and air. The evaporation from the Ander sson evaporimeter at Sidi Bouzid was 0.8-0.9 of that from the Piche at mometer. Any discrepancies were explained by differences in reservoir volume and function of the devices. The small volume of water and the cheapness and convenience of the device in studies of spatial variabil ity of potential evaporation at field scale make it a worthwhile alter native to those currently used.