Fuchun Huang

Potential improvements to statistical downscaling of general circulation model outputs to catchment streamflows with downscaled precipitation and evaporation

An existing streamflow downscaling model (SDM(original)), was modified with the outputs of a precipitation downscaling model (PDM) and an evaporation downscaling model (EDM) as additional inputs, for improving streamflow projections. For this purpose, lag 0, lag 1 and lag 2 outputs of PDM were individually introduced to SDM(original) as additional inputs, and then it was calibrated and validated. Performances of the resulting modified models were assessed using Nash-Sutcliffe efficiency (NSE) during calibration and validation. It was found that the use of lag 0 precipitation as an additional input to SDM(original) improves NSE in calibration and validation. This modified streamflow downscaling model is called SDM(lag0_preci). Then lag 0, lag 1 and lag 2 evaporation of EDM were individually introduced to SDM(lag0_preci) as additional inputs and it was calibrated and validated. The resulting models showed signs of over-fitting in calibration and under-fitting in validation. Hence, SDM(lag0_preci) was selected as the best model. When SDM(lag0_preci) was run with observed lag 0 precipitation, a large improvement in NSE was seen. This proved that if precipitation produced by the PDM can accurately reproduce the observations, improved precipitation predictions will produce better streamflow predictions.

Time-varying character of storm intensity frequency and duration curves

Abstract Recent climate change impact studies suggest that current rainfall intensity-frequency-duration (IFD) curves are likely to change as a result of climate change. In this paper, an effort was made to quantify the changing character of storm IFD curves using data of four consecutive 30-year time slices from 1880 to 2010. The Melbourne Regional Office rainfall data were used for the purposes of the study. Annual maximum series and generalised extreme value distribution were employed to derive the IFD curves using the data of different time slices and the whole period. Results of IFD curves produced from data for the whole period and the current IFD procedure in Australia, described in Australian Rainfall and Runoff (ARR), showed that the former had produced higher intensities for all sub-hourly storms of return periods of 10 to 100 years compared to the latter, and vice versa for return periods below 10 years. For all other storm durations (ie. 1–72 hours) and for short return periods (<10 years), the current ARR method had generated more intense storms. The above results demonstrate that there is a need to conduct further analysis to investigate changing character of storm IFD curves using rainfall data at several stations.