Vegetation Response to Climatic Variability: Implications for Root Zone Storage and Streamflow Predictions

Tempel, Nienke Tessa; Bouaziz, Laurene; Taormina, Riccardo; van Noppen, Ellis; Stam, Jasper; Sprokkereef, Eric; Hrachowitz, Markus

doi:10.5194/egusphere-2024-115

Cited by 3 publications

(6 citation statements)

References 33 publications

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“…The overall estimated magnitudes fall with S umax ~ 95 -115 mm well within the range of long-term average values reported previously for the greater region (e.g. Bouaziz et al, 2021;Hrachowitz et al, 2021;Tempel et al, 2024) and other temperate, humid environments (e.g. Kleidon, 2004;Gao et al, 2014b;de Boer et al, 2016;Wang-Erlandsson et al, 2016;Stocker et al, 2023;van Oorschot et al, 2023).…”

Section: Multi-decadal Changes In Root Zone Storage Capacity Sumaxsupporting

confidence: 88%

“…precipitation and transpiration (e.g., Donohue et al, 2012;Gentine et al, 2012;Gao et al, 2014b;De Boer-Euser et al, 2016;Nijzink et al, 2016a;Dralle et al, 2021;McCormick et al, 2021;Hrachowitz et al, 2021;Stocker et al, 2023;van Oorschot et al, 2021van Oorschot et al, , 2023. For applications of hydrological and land-surface models S umax (or equivalent parameters) has, except for very few exceptions (Wagener et al, 2003;Merz et al, 2011;Bouaziz et al 2022;Tempel et al, 2024) been assumed constant over time. As a major knowledge gap, it remains so far unknown if S umax follows climatic variability and evolves over time, thereby reflecting vegetation adaptation to changing conditions.…”

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confidence: 99%

“…However, several studies have demonstrated that catchments in many regions world-wide experience deviations ΔI E from their expected new I E following a change in I A (e.g. Jaramillo and Destouni 2014;van der Velde et al, 2014;Jaramillo et al, 2018a;Reaver et al, 2022;Tempel et al, 2024).…”

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confidence: 99%

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Multi-decadal fluctuations in root zone storage capacity through vegetation adaptation to hydro-climatic variability has minor effects on the hydrological response in the Neckar basin, Germany

Wang,

Hrachowitz,

Schoups

2024

Preprint

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Abstract. Climatic variability can considerably affect the catchment-scale root zone storage capacity (Sumax) which is a critical factor regulating latent heat fluxes and thus the moisture exchange between land and atmosphere as well as the hydrological response and biogeochemical processes in terrestrial hydrological systems. However, direct quantification of changes in Sumax over long time periods and the mechanistic drivers thereof at the catchment-scale are missing so far. As a consequence, it remains unclear how climatic variability, such as precipitation regime or canopy water demand, affects Sumax and how fluctuations in Sumax may influence the partitioning of water fluxes and therefore, also affect the hydrological response at the catchment-scale. The objectives of this study in the Upper Neckar river basin in Germany are therefore to provide a detailed analysis of multi-decadal changes in Sumax that can be observed as a result of changing climatic conditions over a 70-year period and how this further affects hydrological dynamics. More specifically, we test the hypotheses that (1) Sumax significantly changes over multiple decades reflecting vegetation adaptation to climate variability, (2) changes in Sumax are a dominant control on the evaporative index IE = EA/P and thus on the partitioning of water into drainage and evaporative fluxes as described by deviations ΔIE from parametric Budyko curves over time, (3) changes in Sumax also affect short term hydrological response dynamics and a time-dynamic implementation of Sumax as parameter in a hydrological model can improve the performance of a hydrological model. In this study, based on long-term daily hydrological records (1953–2022) and a stepwise approach over multiple consecutive 20-year periods, we found that variability in hydroclimatic conditions, with aridity index IA (i.e. EP/P) ranging between ~ 0.9 and 1.1 over the study period was accompanied by deviations ΔIE between -0.02 and 0.01 from the expected IE inferred from the long-term parametric Budyko curve. Similarly, fluctuations in Sumax, ranging between ~ 95 and 115 mm or 20 %, were observed over the same time period. While uncorrelated with long-term mean precipitation and potential evaporation, it was shown that the magnitude of Sumax is controlled by the ratio of winter or summer precipitation (p < 0.05). In other words, Sumax in the study region does not depend on the overall wetness condition as for example expressed by IA, but rather on how water supply by precipitation is distributed over the year. However, fluctuations in Sumax were found to be uncorrelated with observed changes in ΔIE. Consequently, replacing a long-term average, time-invariant estimate of Sumax with a time-variable, dynamically changing formulation of that parameter in a hydrological model did not result in an improved representation of the long-term partitioning of water fluxes, as expressed by IE (and fluctuations ΔIE thereof), nor in an improved representation of the shorter-term response dynamics. Overall, this study provides quantitative mechanistic evidence that Sumax significantly changes over multiple decades reflecting vegetation adaptation to climatic variability. However, this temporal evolution of Sumax cannot explain long-term fluctuations in the partitioning of water (and thus latent heat) fluxes as expressed by deviations ΔIE from the parametric Budyko curve over multiple time periods with different climatic conditions. Similarly, it does not have any significant effects on shorter term hydrological response characteristics of the upper Neckar catchment. This further suggests that accounting for temporal evolution of Sumax with a time-variable formulation of that parameter in a hydrological model does not improve its ability to reproduce the hydrological response and may therefore be of minor importance to predict the effects of a changing climate on the hydrological response in the study region over the next decades to come.

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Section: Multi-decadal Changes In Root Zone Storage Capacity Sumaxsupporting

confidence: 88%

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confidence: 99%

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Multi-decadal fluctuations in root zone storage capacity through vegetation adaptation to hydro-climatic variability has minor effects on the hydrological response in the Neckar basin, Germany

Wang,

Hrachowitz,

Schoups

2024

Preprint

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Wang

2024

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Global patterns in vegetation accessible subsurface water storage emerge from spatially varying importance of individual drivers

van Oorschot,

Hrachowitz,

Viering

et al. 2024

Environ. Res. Lett.

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Vegetation roots play an essential role in regulating the hydrological cycle by removing water from the subsurface and releasing it to the atmosphere. However, the present understanding of the drivers of ecosystem-scale root development and their spatial variability globally is limited. This study investigates the varying roles of climate, landscape, and vegetation on the magnitude of root zone storage capacity (Sr) worldwide, which is defined as the maximum volume of subsurface moisture accessible to vegetation roots. To this aim, we quantified Sr and evaluated 21 possible climate, landscape, and vegetation controls for 3612 river catchments worldwide using a random forest machine learning model. Our findings reveal climate as primary, but spatially varying, driver of ecosystem scale Srwith landscape and vegetation characteristics playing a minor role. More specifically, we found the mean inter-storm duration as most dominant control of Sr globally, followed by mean temperature, mean precipitation, and mean topographic slope. While the inter-storm duration, temperature, and slope exhibit a consistent relation with Sr globally, the relation between precipitation and Sr varies spatially. Based on this spatial variability, we classified two different regimes: precipitation driven and energy limited. The precipitation-driven regime exhibits a positive relation between precipitation and Sr for precipitation of up to 3 mm/day, above which the relation flattens and eventually becomes negative. The energy-limited regime exhibits a strictly negative relation between precipitation and Sr. Using the random forest model based on these three dominant climate variables and the landscape variable slope, we generated a global gridded dataset of Sr, which closely resembles other global datasets of root characteristics. This suggests that our parsimonious approach based on four globally available variables to estimate Sr on a global scale has the potential to be readily and easily integrated into the parameterization of Sr in global hydrological and land surface models. This may enhance the accuracy of global predictions of land-atmosphere exchange fluxes and hydrological extremes by providing a robust representation of both spatial and temporal variability in vegetation root characteristics.

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Vegetation Response to Climatic Variability: Implications for Root Zone Storage and Streamflow Predictions

Cited by 3 publications

References 33 publications

Multi-decadal fluctuations in root zone storage capacity through vegetation adaptation to hydro-climatic variability has minor effects on the hydrological response in the Neckar basin, Germany

Multi-decadal fluctuations in root zone storage capacity through vegetation adaptation to hydro-climatic variability has minor effects on the hydrological response in the Neckar basin, Germany

Reply on RC2

Global patterns in vegetation accessible subsurface water storage emerge from spatially varying importance of individual drivers

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