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- Title
Climate controlled root zone parameters show potential to improve water flux simulations by land surface models.
- Authors
van Oorschot, Fransje; van der Ent, Ruud J.; Hrachowitz, Markus; Alessandri, Andrea
- Abstract
The root zone storage capacity (푆r) is the maximum volume of water in the subsurface that can potentially be accessed by vegetation for transpiration. It influences the seasonality of transpiration as well as fast and slow runoff processes. Many studies have shown that 푆r is heterogeneous as controlled by local climate conditions, which affect vegetation strategies in sizing their root system able to support plant growth and to prevent water shortages. Root zone parameterization in most land surface models does not account for this climate control on root development, being based on look-up tables that prescribe worldwide the same root zone parameters for each vegetation class. These look-up tables are obtained from measurements of rooting structure that are scarce and hardly representative of the ecosystem scale. The objective of this research is to quantify and evaluate the effects of a climate controlled representation of 푆r on the water fluxes modeled by the HTESSEL land surface model. Climate controlled 푆r is here estimated with the "memory method" (MM) in which 푆r is derived from the vegetation's memory of past root zone water storage deficits. 푆r,MM is estimated for 15 river catchments over Australia across three contrasting climate regions: tropical, temperate and Mediterranean. Suitable representations of 푆r,MM are implemented in an improved version of HTESSEL (MD) by accordingly modifying the soil depths to obtain a model 푆r,MD that matches 푆r,MM in the 15 catchments. In the control version of HTESSEL (CTR), 푆r,CTR is larger than 푆r,MM in 14 out of 15 catchments. Furthermore, the variability among the individual catchments of 푆r,MM (117-722 mm) is considerably larger than of 푆r,CTR (491-725mm). The climate controlled representation of 푆r in the MD version results in a significant and consistent improvement of the modeled monthly seasonal climatology (1975-2010) and inter-annual anomalies of river discharge compared with observations. However, the effects on biases in long-term annual mean fluxes are small and mixed. The modeled monthly seasonal climatology of the catchment discharge improved in MD compared to CTR: the correlation with observations increased significantly from 0.84 to 0.90 in tropical catchments, from 0.74 to 0.86 in temperate catchments and from 0.86 to 0.96 in Mediterranean catchments. Correspondingly, the correlations of the inter-annual discharge anomalies improve significantly in MD from 0.74 to 0.78 in tropical catchments, from 0.80 to 0.85 in temperate catchments and from 0.71 to 0.79 in Mediterranean catchments. The results indicate that the use of climate controlled 푆r,MM can significantly improve the timing of modeled discharge and, by extension, also evaporation fluxes in land surface models. On the other hand, the method has not shown to significantly reduce long-term climatological model biases over the catchments considered for this study.
- Subjects
AUSTRALIA; ENVIRONMENTAL engineering; WATER shortages; SOIL depth; FLUX (Energy); WATER storage; ROOT development; TROPICAL climate
- Publication
Earth System Dynamics Discussions, 2021, p1
- ISSN
2190-4995
- Publication type
Article
- DOI
10.5194/esd-2021-3