Estimates of water partitioning in complex urban landscapes with isotope‐aided ecohydrological modelling

Abstract

Urban green space is increasingly viewed as essential infrastructure to build resilience to climate change by retaining water in the city landscape and balancing ecohydrological partitioning into evapotranspiration for cooling and groundwater recharge. Quantifying how different vegetation types affect water partitioning is essential for future management, but paucity of data and the complex heterogeneity of urban areas make water balance estimates challenging. Here, we provide a preliminary assessment of water partitioning from different sized patches of trees and grass as well as from sealed surfaces. To do this, we used limited field observations together with an advanced, process‐based tracer‐aided ecohydrological model at a meso‐scale (5 km2) in central Berlin, Germany. Transpiration was the dominant green water flux accounting for over 50% of evapotranspiration in the modelled area. Green water fluxes were in general greater from trees compared with grass, but grass in large parks transpired more water compared with grass in small parks that were intensively used for recreation. Interception evaporation was larger for trees compared with grass, but soil water evaporation was greater for grass compared with trees. We also show that evapotranspiration from tree‐covered areas comprise almost 80% of the total evapotranspiration from the whole model domain while making up less than 30% of the surface cover. The results form an important stepping‐stone towards further upscaling over larger areas and highlights the importance of continuous high‐resolution hydrological measurements in the urban landscape, as well as the need for improvements to ecohydrological models to capture important urban processes.

Enhancing urban runoff modelling using water stable isotopes and ages in complex catchments

“…The actual evapotranspiration estimated within the model (Table S2) was within the range of estimates for previous study sites in Berlin (Gillefalk et al, 2021, 2022; Kuhlemann et al, 2021); however, the water loss estimates were at the low‐end of feasible ranges. The estimates may be lower than expected due to multiple factors, including the lower influence of green space sensitivity due to the calibration bias to blue water fluxes at the sub‐catchment scale, and the differences in model structure on estimation (e.g.…”

“…The actual evapotranspiration estimated within the model (Table S2) was within the range of estimates for previous study sites in Berlin (Gillefalk et al, 2021(Gillefalk et al, , 2022Kuhlemann et al, 2021); however, the water loss estimates were at the low-end of feasible ranges.…”

“…To improve understanding of process interactions and water partitioning in urban landscapes, there has been an increased use of more complex ecohydrological modelling approaches to characterize flux dynamics in urban green spaces (Gillefalk et al, 2022; Ichiba et al, 2018; Meili et al, 2020). Relatively few of these modelling approaches utilize tracers such as water stable isotopes to better constrain water flux estimations (e.g.…”

Integrated monitoring and modeling to disentangle the complex spatio-temporal dynamics of urbanized streams under drought stress

“…Consequently, more hydrological studies are moving towards integrating a more process-based understanding of the spatio-temporal dynamics of the urban water cycle components across the urban critical zone (Arden et al, 2014 ; Cristiano et al, 2020 ; Gillefalk et al, 2022 ; Salvadore et al, 2015 ). Studies investigating urban catchment hydrology have shown significantly lower water ages (Mean Transit Times – MTTs) and higher fractions of young water than non-urban catchment as a result of artificial storm drainage and reduced recharge and groundwater storage under impervious surfaces (Bonneau et al, 2018 ; Kuhlemann et al, 2022 ; Parajulee et al, 2019 ; Soulsby et al, 2015 ; Stevenson et al, 2022 ).…”

“…Ecohydrological processes in urban green spaces have been investigated across scales, ranging from the street scale (Meili et al, 2020 ), to plot and sub-district level (Gillefalk et al, 2021 , 2022 ) for addressing soil water storage dynamics and evapotranspiration, and integrating specific urban effects on ecohydrological fluxes (Meili et al, 2020 ; Ring et al, 2023 ). Urban impacts on groundwater recharge have also been investigated.…”