Preprints
https://doi.org/10.5194/hess-2020-539
https://doi.org/10.5194/hess-2020-539

  31 Oct 2020

31 Oct 2020

Review status: a revised version of this preprint is currently under review for the journal HESS.

Upscaling land-use effects on water partitioning and water ages using tracer-aided ecohydrological models

Aaron A. Smith1, Doerthe Tetzlaff1,2,3, Lukas Kleine1,2, Marco Maneta4, and Chris Soulsby3 Aaron A. Smith et al.
  • 1IGB Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin, Berlin, Germany
  • 2Humboldt University Berlin, Berlin, Germany
  • 3Northern Rivers Institute, School of Geosciences, University of Aberdeen, UK
  • 4School of Geosciences, University of Montana, USA

Abstract. Quantifying how vegetation mediates water partitioning at different spatial and temporal scales in complex, managed catchments is fundamental for long-term sustainable land and water management. Estimations from ecohydrological models conceptualizing how vegetation regulates the inter-relationships between catchment water storage dynamics, evapotranspiration losses, and recharge/runoff fluxes are needed to assess water availability for a range of ecosystem services; and evaluate how these might change under increasing extreme events, such as droughts. Currently, the feedback mechanisms between water and mosaics of different vegetation/land cover are not well understood across spatial scales and the effects of scale on the skill of ecohydrological models needs to be clarified. We used the tracer-aided ecohydrological model EcH2O-iso in an intensively monitored 66 km2 mixed land-use catchment in NE Germany to quantify water flux-storage-age interactions at four model-grid resolutions (250, 500, 750, and 1000 m). This used a fusion of field (including precipitation, soil water, groundwater, and stream isotopes) and remote sensed data in the calibration. Multi-criteria calibration across the catchment at each resolution revealed some differences in the estimation of fluxes, storages, and water ages. Larger grid-resolutions were unable to replicate observed streamflow and distributed isotope dynamics in the way smaller pixels could. However, using isotope data in the calibration still helped in constraining the estimation of fluxes, storage and water ages at coarser resolutions. Despite using the same data and parameterisation for calibration at different grid resolutions, the modelled proportion of fluxes differed slightly at each resolution, with coarse models simulating higher evapotranspiration, lower relative transpiration, increased overland flow, and slower groundwater movement. Although the coarser resolutions also revealed higher uncertainty and lower overall model performance, the overall results were broadly consistent. The study shows that tracers provide effective calibration constraints on larger resolution ecohydrological modelling and help understand the influence of grid-resolution on the simulation of vegetation-soil interactions. This is essential in interpreting associated uncertainty in estimating land-use influence on large-scale blue (ground and surface water) and green (vegetation and evaporated water) fluxes, particularly for future environmental change.

Aaron A. Smith et al.

 
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Aaron A. Smith et al.

Aaron A. Smith et al.

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Short summary
We used a tracer-aided ecohydrological model mixed land-use catchment in NE Germany to quantify water flux-storage-age interactions at four model-grid resolutions. The model's ability for reproducing spatio-temporal flux-storage-age interactions decreases with increasing model grid sizes. Similarly, larger model grids showed vegetation influenced changes in blue and green water partitioning. Simulations reveal the value of measured of soil and stream isotopes for model calibration.