Streamflow decline in southwestern Australia, 1950–2008

Abstract

Southwest Western Australia (SWWA) has experienced a 15–20% reduction in rainfall since the 1970s with severe reductions in inflows to Perth drinking water reservoirs. To quantify rainfall and runoff patterns, we used trend and change point analyses for a 50 year record (1950–2008) and in the last two decades (1989–2008). From 1950–2008, trend tests showed significant declines in annual rainfall and runoff with corresponding change points for both rainfall and flow in the late 1960s or mid‐1970s. In the more recent record (1989–2008), runoff declined in the majority of catchments, but rainfall did not show a significant downward trend. Rather, streamflow decline was observed as a step change in response to the occurrence of below‐average rainfall years. A shift from perennial to ephemeral streams and a decline in the runoff coefficient (runoff/rainfall) in the last decade suggests a new hydrologic regime has developed with important implications for future surface water supply.

Vegetation plays an important role in mediating future water resources

“…Some of these reductions are precipitation-driven, particularly in south-western Australia, and exacerbated by increasing PET ( figure S2). South-western Australia has experienced declining streamflow since the mid-1970s (Petrone et al 2010) and our results thus suggest this trend is likely to continue into the future. A comparison of Budyko and LPX projections shows that the reductions in runoff in south-western Australia are further aggravated when vegetation processes are considered (figure 2).…”

Sudden forest canopy collapse corresponding with extreme drought and heat in a mediterranean-type eucalypt forest in southwestern Australia

“…Decreases in precipitation have corresponded with significant decreases in streamflow and groundwater levels in forested catchments (Croton and Reed 2007;Kinal and Stoneman 2011). Formerly perennial streams are now ceasing to flow for considerable periods each year (Petrone et al 2010), while groundwater levels have fallen up to eleven meters in some regions since 1975 (Croton and Reed 2007). and 1970-2011 illustrating a climate shift described in Bates et al 2008 Corresponding with a prolonged heatwave (nine days greater than 35°C) in late February 2011(BOM 2011b) midstorey and overstorey tree crowns suddenly began dying (collapsing) in several ecosystems in SWWA (Matusick et al 2012).…”

How streamflow has changed across Australia since the 1950s: evidence from the network of hydrologic reference stations

“…Statistical significance testing is commonly used to assess the changes in hydrological datasets (Helsel and Hirsch, 2002;Monk et al, 2011;Hannaford and Buys, 2012). The Mann-Kendall (MK) trend test (Mann, 1945;Kendall, 1975) was adopted in this study to identify statistically significant monotonic increasing or decreasing trends (Petrone et al, 2010;Zhang et al, 2010;Miller and Piechota, 2008). In order to ensure the assumption of independence was met for the MK test, the non-parametric median crossing and rank difference tests (Kundzewicz and Robson, 2000) were applied to entire datasets.…”

“…Several other studies investigated trends of selected streamflow statistics in a particular region, e.g. southwest Australia (Petrone et al, 2010;Durrant and Byleveld, 2009), southeast Australia or Victoria (Tran and Ng, 2009;Stewardson and Chiew, 2009). All these studies addressed the trend analysis of Australian rivers with a limited spatial or temporal coverage of flow data.…”