Climate-controlled root zone parameters show potential to improve water flux simulations by land surface models
<p>The root zone storage capacity (<span class="inline-formula"><i>S</i><sub>r</sub></span>) is the maximum volume of water in the subsurface that can potentially be accessed by vegetation for transpiration. It influences the seasonality of transpi...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-06-01
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| Series: | Earth System Dynamics |
| Online Access: | https://esd.copernicus.org/articles/12/725/2021/esd-12-725-2021.pdf |
| Summary: | <p>The root zone storage capacity (<span class="inline-formula"><i>S</i><sub>r</sub></span>) 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 <span class="inline-formula"><i>S</i><sub>r</sub></span> 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 and is based on lookup tables that prescribe the same root zone parameters worldwide for each vegetation class. These lookup 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 <span class="inline-formula"><i>S</i><sub>r</sub></span> on the water fluxes modeled by the Hydrology Tiled ECMWF Scheme for Surface Exchanges
over Land (HTESSEL) land surface model. Climate-controlled <span class="inline-formula"><i>S</i><sub>r</sub></span> is estimated here with the “memory method” (MM) in which <span class="inline-formula"><i>S</i><sub>r</sub></span> is derived from the vegetation's memory of past root zone water storage deficits. <span class="inline-formula"><i>S</i><sub>r,MM</sub></span> is estimated for 15 river catchments over Australia across three contrasting climate regions: tropical, temperate and Mediterranean. Suitable representations of <span class="inline-formula"><i>S</i><sub>r,MM</sub></span> are implemented in an improved version of
HTESSEL (Moisture Depth – MD) by accordingly modifying the soil depths to obtain a model
<span class="inline-formula"><i>S</i><sub>r,MD</sub></span> that matches <span class="inline-formula"><i>S</i><sub>r,MM</sub></span> in the 15 catchments. In the control version of HTESSEL (CTR), <span class="inline-formula"><i>S</i><sub>r,CTR</sub></span> is larger than
<span class="inline-formula"><i>S</i><sub>r,MM</sub></span> in 14 out of 15 catchments. Furthermore, the variability
among the individual catchments of <span class="inline-formula"><i>S</i><sub>r,MM</sub></span> (117–722 <span class="inline-formula">mm</span>) is considerably larger than of <span class="inline-formula"><i>S</i><sub>r,CTR</sub></span> (491–725 <span class="inline-formula">mm</span>). The climate-controlled representation of <span class="inline-formula"><i>S</i><sub>r</sub></span> in the MD version results in a significant and consistent improvement of the modeled monthly seasonal climatology (1975–2010) and interannual anomalies of river discharge compared with observations. However, the effects on biases in long-term annual mean river discharge 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 interannual 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 <span class="inline-formula"><i>S</i><sub>r,MM</sub></span> 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 been shown to significantly reduce long-term climatological model biases over the catchments considered for this study.</p> |
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| ISSN: | 2190-4979 2190-4987 |