Evaporation trends

Summary

Lake-evaporation rates Eo around the world have been deduced in three ways, using land-based data. The estimates indicate generally decreasing rates of 0.08, 0.13 and 0.05 mm/day per decade respectively, i.e. of the order of 0.1 mm/d·dec. One method of estimation involves a simplified version of the Penman evaporation formula, which shows that the reduction of Eo is due chiefly to the general lessening of solar radiation at the surface. In consequence of the decline of Eo, a two-regime model of the evaporation from land surfaces shows that there has been a decrease in the rate of actual evaporation from land surfaces Ea also, at places where rainfall exceeds Ep, the rate of water loss from a US Class-A pan evaporimeter. This implies increased runoff there. On the other hand, there is a slight increase of Ea in drier seasons and places, which are more common, implying a little more soil moisture.