Title
Hydrologic non-stationarity and modelling implications - 09:00
Speaker
F.H.S. Chiew
Session
Hw15S3 - Testing simulation and forecasting models in non-stationary conditions
Author(s)
Chiew, F.H.S. 1; Potter, N.J. 1; Vaze, J. 1; Petheram, C. 1; Zhang, L. 1; Teng, J. 1; Post, D.A. 1 - 1 CSIRO
Land and Water, Australia
Abstract number
Hw15S3.02
Abstract
This paper will complement the modelling by our group for the experiments set out for the
workshop. Three of the 10+ catchments used for the workshop experiments come south-eastern
Australia. The far south-eastern Australian region is interesting because the recent prolonged 1997–
2009 “Millennium” drought exposed different types of hydroclimate and hydrologic non-stationarity.
The hydroclimate data in this region show very different rainfall-runoff relationship during the
Millennium drought at the annual and other time scales. Annual models developed using pre-1997
data significantly overestimates the post-1997 runoff. Rainfall-runoff models calibrated against pre1997 data also simulates very poorly the post-1997 runoff at all time scales.
The long drought also exposed hydrologic processes that become more dominant in long dry spells.
In particular, the reduced connectivity between surface and subsurface water and farm dams
intercepting proportionally more water during dry periods accentuate the runoff decline from lower
rainfall. Nevertheless, because the Millennium drought has highlighted the importance of these
hydrologic processes and we have now seen the changes in the climate-runoff relationship, we can
adapt hydrological models and use smarter modelling considerations to better simulate these.
Consistent with the focus of this workshop, we will present some of the modelling methods, and
show that these models will then be able to predict near-term changes to runoff resulting from
changes in the climate inputs.
However, predicting changes to runoff further into the future will remain difficult. This is because
future runoff will be impacted by higher temperature and atmospheric CO2 concentrations not seen
in past records, as well as the complex interactions and feedbacks between various variables and
processes (many of which are not yet known) in a warmer and higher CO2 environment.