Abstract Conceptual rainfall‐runoff models are widely used for hydrological applications, yet many fail to capture multi‐annual storage dynamics that are critical during prolonged droughts or shifting climate conditions. This study investigates whether specific structural components enable models to represent such long‐term behavior. We hypothesize that three components are necessary: (a) a store responsible for long‐term behavior, (b) disconnection of that store from direct streamflow generation, and (c) a water loss mechanism from that store (e.g., evapotranspiration or groundwater export) that allows gradual depletion. We systematically tested this hypothesis using 46 daily models from the Modular Assessment of Rainfall‐Runoff Models Toolbox. Each model was tested in three Australian headwater catchments that have previously been identified as subject to multi‐annual declines in storage during the “Millennium” Drought (1997–2010). In addition, we included a synthetic scenario designed to evaluate delayed streamflow recovery after an idealized multi‐annual drought. Models with all three structural components were significantly more successful: 5 of these 9 models passed both tests, compared to much lower success rates (1 model) among the 37 without the full structure. However, structure alone was not sufficient, as some models with the hypothesized structure failed due to restrictive internal formulations or calibration outcomes that prevented activation of the intended slow‐storage processes. These findings provide guidance for identifying or adapting conceptual models in applications where hydrological memory and long‐term drought response are important.
Zhang et al. (Sun,) studied this question.