Symptoms of performance degradation during multi-annual drought: a
large-sample, multi-model study
Abstract
Hydrologic models are essential tools to understand and plan for the
effect of changing climates; however, they are known to underperform in
transitory climate conditions. Research to date identifies the
inadequacy of models to perform during prolonged drought, but falls
short on pinpointing how and which specific aspects of model performance
are affected. Here, we study five conceptual rainfall-runoff models and
their performance in 155 Australian catchments which recently
experienced a 13-year long dry period, with a focus on a wide range of
performance metrics. We show that model performance degrades extensively
during the drought across most metrics, with overestimation of flow
volumes driving the decline and representation of shape and variability
of the hydrograph and the flow-duration curve being more resilient to
the prolonged dry climate. This indicates that the overestimation is not
linked to specific flow regimes, but is the result of proportional flow
decline throughout the hydrograph, suggesting engagement of multiple
catchment processes in determining the changes in flow during the
drought across high and low flow periods as well as through faster and
slower flow routes. Additionally, we show that in most cases model
performance does not recover after the end of the drought and that the
multi-annual nature of the drought is the likely reason for exacerbated
performance decline due to accumulation and aggravation of errors over
subsequent dry years. By promoting detailed investigation of models’
shortcomings, we hope to foster the development of more resilient model
structures to improve applicability within climate change scenarios.