Abstract
Abstract. In this study, we propose a new formulation of subsurface water storage dynamics for use in rainfall–runoff models. Under the assumption of a strong relationship between storage and runoff, the temporal distribution of catchment-scale storage is considered to have the same shape as the distribution of observed recessions (measured as the difference between the log of runoff values). The mean subsurface storage is estimated as the storage at steady state, where moisture input equals the mean annual runoff. An important contribution of the new formulation is that its parameters are derived directly from observed recession data and the mean annual runoff. The parameters are hence estimated prior to model calibration against runoff. The new storage routine is implemented in the parameter parsimonious distance distribution dynamics (DDD) model and has been tested for 73 catchments in Norway of varying size, mean elevation and landscape type. Runoff simulations for the 73 catchments from two model structures (DDD with calibrated subsurface storage and DDD with the new estimated subsurface storage) were compared. Little loss in precision of runoff simulations was found using the new estimated storage routine. For the 73 catchments, an average of the Nash–Sutcliffe efficiency criterion of 0.73 was obtained using the new estimated storage routine compared with 0.75 using calibrated storage routine. The average Kling–Gupta efficiency criterion was 0.80 and 0.81 for the new and old storage routine, respectively. Runoff recessions are more realistically modelled using the new approach since the root mean square error between the mean of observed and simulated recession characteristics was reduced by almost 50 % using the new storage routine. The parameters of the proposed storage routine are found to be significantly correlated to catchment characteristics, which is potentially useful for predictions in ungauged basins.
Highlights
The movement of groundwater to streams is an important component of catchment hydrology and simulating its movement is key to accurately reproducing the hydrograph
At the spatial scale of interest for studying the dynamics of hydrological systems, we are not able to see and learn how water is transported in the subsurface
The proposed subsurface storage model is based on linear reservoir theory and its parameters are derived directly from recession analysis, digitised maps and the mean annual runoff
Summary
The movement of groundwater to streams is an important component of catchment hydrology and simulating its movement is key to accurately reproducing the hydrograph. At the spatial scale of interest for studying the dynamics of hydrological systems (the catchment scale), we are not able to see and learn how water is transported in the subsurface. The subsurface water storage, hereafter denoted subsurface storage or storage, is to be understood as the dynamics storage, i.e. the variation in storage between the wet and dry periods (Kirchner, 2009). We will develop and test a new formulation for storage dynamics. The proposed subsurface storage model is based on linear reservoir theory and its parameters are derived directly from recession analysis, digitised maps and the mean annual runoff
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