The concept of the water storage continuum to increase ecohydrological resilience of mesoscale catchments

Subsurface storage is inherently difficult to quantify, but strongly affect the ecohydrological resilience of landscapes, which can be defined as the degree to which catchment can maintain key aspects of physical functionality in terms of water resource provisioning and biomass production in response to climatic and other stressors such as drought. These functions, and in particular storage dynamcis, are commonly studied in small-scale experimental settings, at larger regional scales or from purely modelling perspectives. To move the field forward, we urgently need to better characterise and quantify the 3-dimensional water storage continuum at mesoscale catchment (10¹-10² km²), as its this scale which is most tangible and relevant for land managers, and where physical process-based evidence can still be obtained to understand how sensitivities change between zones of deficit and storage during periods of drought. We present findings from a long-term, drought sensitive experimental catchment in Germany. We integrated extensive hydrometric and water stable isotope approaches into tracer-aided modelling to quantify spatial and temporal storage dynamics. We argue that a spatially distributed understanding of how underlying ecohydrological processes affect drought evolution at the mesoscale is fundamental for future assessment of water storage dynamics, water availability and provision of wider ecosystem services in a changing climate. As such, this proposed approach can form science-based evidence for new concepts on the regulation of catchment ecosystem services and help building societal resilience to droughts.