Assessing the value of high-resolution isotope tracer data in the stepwise development of a lumped conceptual rainfall-runoff model

A study was undertaken in a small agricultural catchment in north east Scotland with the objective of assessing the value of high-resolution isotope data for integration within a lumped, conceptual hydrological model to improve calibration and aid evaluation. Daily samples of precipitation and stream flow, collected over a year, were analysed for deuterium using new laser spectroscopy technology. The utility of such high-resolution isotope data was evaluated in relation to the associated uncertainty which was contextualized in relation to uncertainties over hydrometric data and the influence of different sampling resolutions. The simulations were evaluated against model and data errors using auxiliary stream deuterium time series in addition to discharge. The lumped conceptual catchment isotope model (CIM) was developed and adequately reflects flow dynamics and deuterium peaks, but a simple assumption of 'good mixing' is not able to fully reproduce the daily stream deuterium dynamic. Using auxiliary data for model evaluation, however, significantly constrained acceptable behavioural parameter sets and therefore reduces the model's degree of freedom. The data indicate that isotopic variability in the stream response is not adequately captured using weekly tracer data. The input resolution of precipitation deuterium concentrations, which were much more variable, proved to be crucial. This approach has provided further assessment of the value of tracers in hydrological modelling, demonstrating their usefulness in terms of model conceptualization, development and calibration, which outweighs the additional uncertainty. Copyright (C) 2010 John Wiley & Sons, Ltd.