potential-impacts-of-climate-change-on-the-swan-and-canning-rivers

<strong>of</strong> 1964 is considered a 1-in-50 year fl ood event, but was the combination <strong>of</strong> two very wet winter
months followed by a 1-in-20 year rainfall event. Antecedent wetness and regional groundwater
levels are generally lower since the rainfall decrease <strong>of</strong> the mid 1970s. Monitoring <strong>of</strong> bauxite catchments
has shown signifi cant falls in regional groundwater levels (Croton, pers. comm.). This will
have consequent implications for future fl ood magnitudes <strong>of</strong> all frequencies.
Extreme summer rainfall events as a cause <strong>of</strong> summer flooding
Research to date has not found a statistically signifi cant trend in the <strong>change</strong> in summer rainfall extremes
over time (e.g. Li et al. 2005 and other unpublished IOCI related studies).
Water Quality
In the recent report <strong>of</strong> water quality trend analysis for the Swan Canning river system, Henderson
and Kuhnert (2004) used regression models to investigate the spatial and temporal trends <strong>of</strong> environmental
variables from 1995 to 2004. The results are summarised in Table 9 for the major areas
<strong>of</strong> the Swan Canning river system. The results suggest a decreasing trend in total and oxidised
nitrogen and phosphorus throughout most <strong>of</strong> the system. There was also a general decreasing trend
in chlorophyll-a.
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