Applications of a Thermal-Based Two-Source Energy Balance Model Coupling the Sun-Induced Chlorophyll Fluorescence Data

Quantifying and monitoring land surface evapotranspiration (ET) is an essential task for understanding the earth's water, energy, and carbon cycles. ET, specifically plant transpiration ( T ), is closely linked to the photosynthesis, which is coupled through stomatal function. However, the mechanistic links between sun-induced chlorophyll fluorescence (SIF) information indicating canopy photosynthetic activity and $T$ are complex and difficult to derive empirically. An empirical SIF- $T$ relationship at ecosystem scale was developed and coupled to the two-source energy balance model (TSEB-SIF) to estimate the ET and its components, $T$ and soil evaporation, E . By comparing model predictions with observations from an irrigated cropland site located in a semiarid region, the TSEB-SIF model shows a slightly better performance to the TSEB model in estimating ET, especially under water deficit conditions. Moreover, the TSEB-SIF model more reliably partitioned the $T$ from ET, while the TSEB model tended to overestimate the contribution of T to ET.