Time-Space Trend Analysis in Pan Evaporation over Kingdom of Thailand

Abstract

To grasp the temporal and spatial distribution characteristics of the pan evaporation amount in the Chao Phraya River basin, in the Kingdom of Thailand, the writers performed an analysis over a period of 19 years, from 1982 to 2000, where data related to the target area were available. Geographic, seasonal, and annual changes were studied. As a result of performing trend tests on annual changes, negative trends were found in 24 out of 27 observation stations. Furthermore, nine of those locations had a significant negative trend. As a result of performing tests of concurrent rainfall over the same period, although there were positive trends in 8 locations and negative trends in 19 locations, no significant trend—either positive or negative—was obtained. This result does not match a finding that precipitation increase decreases pan evaporation in the United States, a finding that can be derived from the complementary relationship.