4.7 Article

Implementation of Dynamic Effective Rooting Depth in Evapotranspiration Model Deepens Understanding of Evapotranspiration Partitioning Under Soil Moisture Gradients in China

Journal

WATER RESOURCES RESEARCH
Volume 58, Issue 11, Pages -

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2022WR032962

Keywords

plant rooting depth; transpiration; evapotranspiration; soil moisture; PT-JPL model; vegetation change

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Evapotranspiration (ET) is an important process in the water cycle, influenced by below-ground and above-ground vegetation dynamics. This study focuses on the effects of Zr, a measure of rooting depth, on ET and improves modeling performance by incorporating Zr in the PT-JPL model. The results show that the PT-JPLzr model performs better than the PT-JPLsm model, with lower error between modeled and observed ET. Zr influences the sensitivity of transpiration to soil moisture deficit, and soil moisture and LAI are key drivers of T/ET variability in different regions.
Evapotranspiration (ET) is a key component of water cycle and is strongly modulated by below-ground (e.g., dynamic effective rooting depth, Zr) and above-ground (e.g., LAI and canopy height, CH) vegetation dynamics. Existing studies mainly focus on the effect of above-ground vegetation dynamics on ET, while it is still unclear how Zr affects ET. Moreover, it is challenging to parameterize Zr dynamically in large-scale hydrological and biogeochemical models due to data scarcity. Here, we estimate Zr in China from 1982 to 2015 based on Guswa's carbon cost-benefit model, and update ET partitioning algorithm by replacing CH with Zr in PT-JPLsm model to form the PT-JPLzr model. We find that root mean square error (RMSE) between modeled (based on PT-JPLzr model) and observed ET is 8.25% lower than that of PT-JPLsm model at 16 in-situ ET observation sites. Comparing with T/ET from the satellite-based products, our results highlight the improved performance of PT-JPLzr (R-2 = 0.66) due to incorporated Zr, which is superior to that of PT-JPLsm model (R-2 = 0.62). Transpiration (T) limited by changes in soil moisture (SM) is more sensitive to Zr than CH. Thus, Zr improves the PT-JPL model performance by affecting the sensitivity of T to soil moisture deficit. Moreover, SM and LAI are main drivers of T/ET spatial variability in drier and wetter regions, respectively. These findings highlight the critical role of Zr in regulating the effects of soil moisture deficit on ET.

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