Abstract
AbstractUnderstanding the interactions of vegetation and soil water under varying hydrological conditions is crucial to aid quantitative assessment of land‐use sustainability for maintaining water supply for humans and plants. Isolating and estimating the volume and ages of water stored within different compartments of the critical zone, and the associated fluxes of evaporation, transpiration, and groundwater recharge, facilitates quantification of these soil–plant‐water interactions and the response of ecohydrological fluxes to wet and dry periods. We used the tracer‐aided ecohydrological model EcH2O‐iso to examine the response of water ages of soil water storage, groundwater recharge, evaporation, and root‐uptake at a mixed land use site, in northeastern Germany during the drought of 2018 and in the following winter months. The approach applied uses a dynamic vegetation routine which constrains water use by ecological mechanisms. Two sites with regionally typical land‐use types were investigated: a forested site with sandy soils and a deep rooting zone and a grassland site, with loamier soils and shallower rooting zone. This results in much younger water ages (<1 year) through the soil profile in the forest compared to the grass, coupled with younger groundwater recharge. The higher water use in the forest resulted in a more pronounced annual cycle of water ages compared to the more consistent water age in the loamier soil of the grasslands. The deeper rooting zone of the forested site also resulted in older root‐uptake water usage relative to soil evaporation, while the grassland site root‐uptake was similar to that of soil evaporation. Besides more dynamic water ages in the forest, replenishment of younger soil waters to soil storage was within 6 months following the drought (cf. >8 months in the grassland). The temporal evaluation of the responsiveness of soil and vegetation interactions in hydrologic extremes such as 2018 is essential to understand changes in hydrological processes and the resilience of the landscape to the longer and more severe summer droughts predicted under future climate change.
Highlights
Many regions worldwide have been under increasing duress from warmer, drier summers, with long-term projections showing likely future exacerbation of these conditions (King & Karoly, 2017; Quesada, Vautard, Yiou, Hirschi, & Seneviratne, 2012)
At the grassland and forest plot sites in northeast Germany examined in this study, green water fluxes of evaporation and transpiration were dominant in the summer drought of 2018, with only limited blue water fluxes to groundwater recharge following rainfall events
Despite the recovery of soil moisture in the grassland following the drought, fractional water ages in the deeper soil layers suggest that the grassland had not fully recovered from the drought more than half a year after the end of the drought
Summary
The study site is in an agriculturally-dominated catchment, with longterm monitoring for hydrology and stream water chemistry, known as the Demnitzer Millcreek catchment (Smith, Tetzlaff, Gelbrecht, Kleine, & Soulsby, 2020). The performance of the model against MODIS datasets were evaluated only using the MAE due to the uncertainty of variability, the relatively large grid encompassing multiple vegetation and soil types, and the larger time-step of the MODIS datasets The KGE and NSE were used simultaneously to optimize the simulations to soil moisture (%q) dffiffiffiaffiffiffitffiaffiffiffisffiffieffiffitffiffisffiffiffiffiwffiffiffiffiiffitffiffihffiffiffiffiffisffiffiiffigffiffinffiffiffiiffifffiffiifficffiffiaffiffiffinffiffitffiffiffi temporal variability. To test the principal factors in the quantity and responsiveness of storages, fluxes, and water ages, different combinations of soil (sandy loam (grassland) and loamy sand (forest)) and vegetation (grass and forest) were evaluated against the calibrated simulations (referred to as the baseline conditions). The effects of changing the soil under the grass (sandy loam to loamy sand) and vegetation on sandy loam (grass to forest) was evaluated using the 100 “best” calibrated simulations at the grassland site as baseline conditions. The percent change and significance levels were estimated for the whole time-series and the drought and recovery periods
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
