Abstract
Long-term variation in pan evaporation and its origins in Sri Lanka were investigated using trend analyses of several observations. Time series data related to pan evaporation show decreasing trends during 1951-1973 and during 1974-1993 over most climatic zones. In 1974-1993, the decreasing trend was attributed to solar dimming with increasing cloud amounts in view of the following evidence: (1) outgoing long-wave radiation decreased around Sri Lanka; (2) pan evaporation decreased, although it is in a wet climatic zone; (3) sunshine duration decreased; and (4) the radiative term in the Penman equation has a large portion in potential evaporation because of typical circumstances over Sri Lanka.
