Preprints
https://doi.org/10.5194/esd-2021-3
https://doi.org/10.5194/esd-2021-3

  16 Feb 2021

16 Feb 2021

Review status: this preprint is currently under review for the journal ESD.

Climate controlled root zone parameters show potential to improve water flux simulations by land surface models

Fransje van Oorschot1,2, Ruud J. van der Ent1, Markus Hrachowitz1, and Andrea Alessandri2,3 Fransje van Oorschot et al.
  • 1Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands
  • 2Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands
  • 3Institute of Atmospheric Sciences and Climate, National Research Council of Italy (CNR-ISAC), Bologna, Italy

Abstract. The root zone storage capacity Sr 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 Sr 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 Sr on the water fluxes modeled by the HTESSEL land surface model. Climate controlled Sr is here estimated with the memory method (MM) in which Sr is derived from the vegetation's memory of past root zone water storage deficits. Sr,MM is estimated for 15 river catchments over Australia across three contrasting climate regions: tropical, temperate and Mediterranean. Suitable representations of Sr,MM are implemented in an improved version of HTESSEL (MD) by accordingly modifying the soil depths to obtain a model Sr-MD that matches Sr,MM in the 15 catchments. In the control version of HTESSEL (CTR), Sr,CTR is larger than Sr,MM in 14 out of 15 catchments. Furthermore, the variability among the individual catchments of Sr,MM (117–722 mm) is considerably larger than of Sr,CTR (491–725 mm) The climate controlled representation of Sr 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 Sr,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.

Fransje van Oorschot et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2021-3', Anonymous Referee #1, 15 Mar 2021
    • AC1: 'Reply on RC1', Fransje van Oorschot, 23 Apr 2021
  • RC2: 'Valuable contribution to the climate – hydrology interaction topic', Stefan Hagemann, 17 Mar 2021
    • AC2: 'Reply on RC2', Fransje van Oorschot, 23 Apr 2021
  • RC3: 'Comment on esd-2021-3', Andrew Guswa, 17 Mar 2021
    • AC3: 'Reply on RC3', Fransje van Oorschot, 23 Apr 2021

Fransje van Oorschot et al.

Fransje van Oorschot et al.

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Short summary
The roots of vegetation largely control the Earth's water cycle by transporting water from the subsurface to the atmosphere, but are not adequately represented in land surface models, causing uncertainties in modeled water fluxes. We replaced the root parameters in an existing model with more realistic ones that account for a climate control on root development, and found an improved timing of modeled river discharge. Further extension of our approach could improve modeled water fluxes globally.
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