Satellite-derived spatiotemporal data on imperviousness for improved hydrological modelling of urbanised catchments

Conceptual rainfall-runoff models have been used extensively to simulate streamflow in urban catchments. However, spatiotemporal changes in the impervious surface area, as an important land use indicator for urban environment, has not been used explicitly as input into conceptual rainfall-runoff models. In this study, spatiotemporal impervious surface fraction (ISF) data were incorporated into two lumped and distributed (1 km) models, namely SIMHYD and AWBM in an urbanized catchment in southeast Queensland, Australia. A sub-pixel classification technique was used to derive ISF from 6 LandSat images between 1988 and 2015. Daily rainfall -runoff models were calibrated with ISF as an input variable. To evaluate model performance for different simulation periods, four model runs including M1 (lumped models with constant ISF), M2 (lumped models with temporally varying ISF), M3 (distributed models with fixed spatial ISF) and M4 (distributed models with spatiotemporal ISF and climate data). Results showed that (1) the sub-pixel classification algorithm can be used to accurately derive ISF data with a mean absolute error (MAE) ranging from 0.07 to 0.12 for 6 images, (2) ISF in the catchment has increased gradually from 12.2% to 34.6% from 1988 to 2015, (3) the performance of SIMHYD and AWBM were not improved noticeably when distributed climate and ISF data were used, (4) simulation capability of lumped and distributed SIMHYD and AWBM were improved (e.g., increase in NSE from 0.68 to 0.73, and decrease in PBIAS from-30.2% to 1.2% for lumped SIMHYD) when temporal (M2) and/or spatio-temporal (M4) ISF data (5-year) were used, (5) difference in model performance is small and insignificantly whether annual or 5-yearly ISF data were used and (6) annual streamflow would increase by 6.9-7.3 mm (equal to 2.9-3%) in response to every 1% increase in ISF for the catchment tested. The methodology developed in this study can be applied for assessment of the effect of urbanisation on regional water balance.