Evaportion from U.S. Class A Pan of Hill-Evergreen Forest at Doi Pui, Chiengmai

Abstract

Evaporation was measured by U.S. Class A Pan from 1965 through 1970 at Kog-Ma Watershed Research Station, in which locating approximately 1350 meters from mean sea level at latitude 18C 45N. and longitude 98C55E. It was found that summer (February to May) showed higher monthly evaporation approximately 116.6- 189.4 mm, with maximum value in march, wet season (June to October )the second with 68.8-82.8 mm, and winter(November to January) the least. The details were summarized in Table l. High solar radiation and low atmospheric humidity indicated larger amount of monthly evaporation in summer, and also including longwave radiation influenced the vaporization from pan. Cloudy sky and fog caused less evaporation in wet condition. Winter evaporation mostly affected by solar radiation, low humidity,longwave radiation from soil and surrounding stands of climatic station.