Rainfall Variability in the Shoalhaven River Catchment and its Relation to Climatic Indices

The management of the Shoalhaven River, in southern Australia, is important for water supply and floodplain issues including flooding and acid sulphate soil management. Analysis of the spatial variation in rainfall was performed in order to assess temporal and geographical variability within this east Australian catchment and its relationship to large-scale climate drivers, such as the Southern Oscillation Index (SOI), the Interdecadal Pacific Oscillation (IPO), particularly in its negative phase, and the Atmospheric Blocking Index. A total of 141 rain gauges located within a 10-km buffer around the perimeter of the Shoalhaven catchment provided rainfall information spanning from 1885 to 2011. The highest annual mean was in 1950 (1670 mm), with other wet years in 1959 (1564 mm) and 1974 (1571 mm), and the lowest mean was in 1982 (440 mm) and 1944 (446 mm). In the calendar year of 2011 (922 mm), March accounted for 14.5 % of the annual rainfall while April, May and September accounted for less than 5 %. Interpolation between rainfall gauges indicated that the highest rainfall areas occurred in the lower catchment, adjacent to the coast, where there is a pronounced orographic effect. Although it has been implied that drought in this region is related to El Niño years, there was only a weak positive correlation between catchment rainfall and SOI which was moderately enhanced during negative phases of IPO. Seasonal influence of Atmospheric Blocking could be detected on the rain-gauge records during April–October. These findings provide insights not only for this catchment but also for other parts of southeast Australia, implying that coastal catchments may not have strong linkages to key climatic drivers as previously inferred, and management actions and planning on the basis of these climatic indices are not recommended.