Events

Streamflow Decline in South-west Western Australia: Groundwater and Surface Water Threshold Response in a Changing Climate

Dr Kevin Petrone
CSIRO Land and Water
Water for a Healthy Country Flagship

Abstract

A 10-20% reduction in rainfall in the catchments of the Darling Plateau
of south-west Western Australia (SWWA) over the last thirty years has
resulted in a 50 to 70% decline in streamflow to Perth dams. This
decline is most pronounced in small headwater catchments, and streams
that were once perennial have recently ceased to flow in the winter
months. The cause of the amplified streamflow decline is the subject of
a major project funded by the WA Water Foundation (formerly WA Premier’s
Water Foundation). Here we examine a 20 year runoff and rainfall record
for 14 catchments in the high rainfall zone. We found that 13 of 14
catchments showed a significant negative trend in runoff. While rainfall
decline is well documented over the last 50 years in SWWA (BoM 2009), we
did not observe significant rainfall decline since the late 1980s. This
observation suggests that other catchment factors may be driving recent
non-linearity between rainfall and runoff.

To examine the specific hydrologic mechanism for hydrologic response, we
examined a minimally disturbed catchment with a continuous record of
rainfall, runoff and groundwater depth. For this catchment, we observed
a significant decrease in annual runoff (270 to 102 mm), runoff ratio
(0.48 to 0.18), and average depth to the watertable (2.1 to 4.3m) over
the 1989 to 2008 period. Further, negative relationships between depth
to groundwater and runoff ratio suggest that changes catchment storage
and the mechanism for streamflow generation may have changed appreciably
in small headwater catchments with important implications for water
yield. Simple hydrologic modelling (IHACRES) supports this assertion,
with residual error between modelled and observed runoff increasing
steadily over the last decade. We hypothesize that a reduction in the
saturated area adjacent to the stream has created a threshold response
that has accentuated the runoff decline in a changing climate in SWWA.

About the speaker

Kevin Petrone is a research scientist with CSIRO Land and Water in
Perth. He received his Bachelor of Arts in Biology from Hampshire
College, Amherst in Massachusetts, USA in 1993 and was awarded a
doctorate from the University of Alaska, Fairbanks, Alaska, USA in 2005.
Before joining CSIRO, he was a Carl Tryggers Postdoctoral Fellow at the
Swedish University of Agricultural Sciences. His work has focused on
climate change in pristine catchments in Alaska and Sweden, where he
examined the effects of permafrost, fire, wetlands and snowmelt
processes on carbon, nitrogen and solute flux from boreal forests.

More recently Dr Petrone’s work has focused on disturbed catchments in
Western Australia and Tasmania with varying degrees of forest,
agriculture and urban-dominated land-use. He is currently examining how
different land uses influence water, energy and nutrient transport in
natural and modified catchments. This research, being delivered through
CSIRO’s Water for a Healthy Country Flagship, is guiding the restoration
of Australian catchments in the face of changing climate and hydrologic
conditions.



This event is free of charge

For further details email Anne McKenzie < This e-mail address is being protected from spambots. You need JavaScript enabled to view it '; document.write( '' ); document.write( addy_text89014 ); document.write( '<\/a>' ); //--> This e-mail address is being protected from spambots. You need JavaScript enabled to view it >
or phone (08) 9333 6221