Up-scaling the latent heat flux from instantaneous to daily-scale: A comparison of three methods

Abstract

Study region: Two typical flux towers and surrounding 100 km × 100 km areas in Northern China. Study focus: Up-scaling the instantaneous latent heat flux (LE) to daily-scale is an important step for estimate daily evapotranspiration based on satellite observations. This study evaluated the performance three up-scaling methods: constant evaporation fraction (CEF), diurnal LE variation (DLEV) and geosynchronous satellite (GS) by using flux tower and satellite observations at site-scale and regional scales, respectively. The purpose was to improve the accuracy of up-scaling LE. New hydrological insights for the region: The results suggested that: (1) DLEV showed slightly better accuracy (rRMSE = 16.27–26.33%) in estimating daily LE than CEF (rRMSE = 17.21–25.14%) at site-scale; (2) At regional scale, GS showed best accuracy (rRMSE = 34.05%), followed by DLEV (rRMSE = 36.46%), CEF had the worst accuracy (rRMSE = 38.96%); (3) DELV can accurately describe the LE variation during the 8:00–17:00 and show a good agreement with flux tower observations and GS observations, but DLEV cannot guarantee the estimation accuracy outside of this period. In general, this study provided a reference for understanding diurnal LE variation during a single day. Additionally, The DLEV proposed in this study can provide a better up-scaling accuracy of regional LE estimation than the CEF which is currently commonly used.

Keywords

• Up-scaling
• Instantaneous
• Geosynchronous satellite
• Diurnal variation
• Evaporation fraction