Rainfall—runoff model performance suggests a change in flow regime and possible lack of catchment resilience

Abstract

Climate change over the last four decades has resulted in a significant decline in streamflow in south-west Western Australia. In many streams in the region flows have reduced and perennial streams have become ephemeral. This has been accompanied by a decline in groundwater levels. To study this, a suite of five rainfall-runoff models was calibrated against observed flow in 106 gauged catchments across the region. A linear combination of two models, Sacramento and IHACRES, consistently resulted in a better model fit than any other combination of the individual models and this 'adopted model' was used to study catchment behaviour. In many of the catchments, there was a systematic and pervasive drift in model error during the latter period, indicating a change in state in the catchments that was not captured by the models. An assessment of the suitability of model structure is made on the basis of these results.