Assessing the Catchment Storage Function Through a Dual‐Storage Concept

Abstract

AbstractCatchment storage controls most ecohydrological processes by modulating, among other things, the hydrological connectivity between landscape units. However, little is known about the internal dynamics of storage and its feedback with hydraulic connectivity. Here we evaluate the capability of a combined lumped approach (i.e., combining catchment water balance and recession analysis) to partition total dynamic storage (from the water balance) into hydraulically connected (the part feeding stream estimated from recession analysis) and hydraulically disconnected components (i.e., the remaining storage driven by precipitation and evapotranspiration). Results from our combined approach were compared to a point measurement‐based estimation (using wells and soil moisture data) from the experimental Weierbach catchment in Luxembourg (0.45 km2). We found good agreement for the hydraulically connected storage but contrasted results for the hydraulically disconnected storage. During wet periods, the latter were characterized by opposite dynamics and our lumped approach showed step‐by‐step deviations. Overall, these results indicated a good capability of our approach to partition storage, as well as its sensitivity to systematic and random deviations. Considering these possible deviations, this new conceptualization of storage provides relevant and quantifiable information about catchment state (i.e., storage dominated or release dominated). This is further highlighted when represented in a dual‐storage plot (hydraulically disconnected vs. connected storage). Compared to classic storage‐discharge relationships, it allows catchment efficiency (capacity of the catchment to convert storage into streamflow) to be assessed without the need for additional data. We expect that this mechanistic conceptualization of the storage function will provide new opportunities for assessing catchment functioning and catchment classification.