Detectability of day‐to‐day variability in the evaporative flux ratio: A field examination in the Loess Plateau of China

Abstract

The ratio of latent heat flux to available energy, termed the evaporative fraction (EF), and the ratio of latent heat flux to downward shortwave radiation (ES), are two useful evaporative flux ratios (EFR) for estimating daily evaporation. Both EF and ES remain relatively constant during daytime, but their value varies from day to day. It is yet unclear if long‐term change signals are detectable given the uncertainty associated with the diurnal variations. Using EF and ES data obtained during the major rainy seasons on a tableland of the Loess Plateau of China, we showed that day‐to‐day variability in the EF or ES was detectable given diurnal variation. The EF and ES showed slight increasing trends from midmorning to afternoon, but the ES was superior to the EF for satellite‐based monitoring of long‐term evaporation trends.