Assessment of spatial and temporal distribution of reference evapotranspiration and pan evaporation in Taiwan

Evapotranspiration (ET) is an important process of water transfer in the hydrosphere and atmosphere; it plays an active role in the hydrological cycle. Evaporation pan (E_pan) data are often used to estimate reference evapotranspiration (ET_ref) for use in water resource planning. Generally, ET_ref is estimated as the product of the Epan data and a pan coefficient (K_p) (ET_ref = K_p×E_pan). In recent years, due to global climate change, the early studies on Kpan have not reflected the current climatic situation. In this study, the Penman-Monteith reference evapotranspiration, pan evaporation, and pan coefficient are calculated, compared, and regionally mapped at twenty meteorological stations during 1990-2008 in Taiwan. Their spatial and temporal distributions are examined and discussed. The results show the reference evapotranspiration and pan evaporation have similar regional distribution patterns in the Taiwan area both with the highest values being in the southwestern region and the lowest values being in the central region. This distribution pattern provides valuable information for regional hydrological studies since it is a key parameter in regional water resources assessment and water management.