Explaining changes in rainfall–runoff relationships during and  after Australia's Millennium Drought: a community perspective

K. Fowler; M. Peel; M. Saft; T. J. Peterson; A. Western; L. Band; L. Band; C. Petheram; S. Dharmadi; K. S. Tan; L. Zhang; P. Lane; A. Kiem; L. Marshall; L. Marshall; A. Griebel; B. E. Medlyn; D. Ryu; G. Bonotto; C. Wasko; A. Ukkola; C. Stephens; A. Frost; H. Gardiya Weligamage; P. Saco; H. Zheng; F. Chiew; E. Daly; G. Walker; R. W. Vervoort; J. Hughes; L. Trotter; B. Neal; I. Cartwright; R. Nathan

doi:10.5194/hess-26-6073-2022

Hydrology and Earth System Sciences (Dec 2022)

Explaining changes in rainfall–runoff relationships during and after Australia's Millennium Drought: a community perspective

K. Fowler,
M. Peel,
M. Saft,
T. J. Peterson,
A. Western,
L. Band,
L. Band,
C. Petheram,
S. Dharmadi,
K. S. Tan,
L. Zhang,
P. Lane,
A. Kiem,
L. Marshall,
L. Marshall,
A. Griebel,
B. E. Medlyn,
D. Ryu,
G. Bonotto,
C. Wasko,
A. Ukkola,
C. Stephens,
A. Frost,
H. Gardiya Weligamage,
P. Saco,
H. Zheng,
F. Chiew,
E. Daly,
G. Walker,
R. W. Vervoort,
J. Hughes,
L. Trotter,
B. Neal,
I. Cartwright,
R. Nathan

Affiliations

K. Fowler: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
M. Peel: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
M. Saft: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
T. J. Peterson: Department of Civil Engineering, Monash University, Clayton, Victoria, Australia
A. Western: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
L. Band: Department of Environmental Science, University of Virginia, Charlottesville, Virginia, USA
L. Band: Department of Engineering Systems and Environment, University of Virginia, Charlottesville, Virginia, USA
C. Petheram: CSIRO Land and Water, Sandy Bay, Tasmania, Australia
S. Dharmadi: Department of Environment, Land, Water and Planning, Melbourne, Victoria, Australia
K. S. Tan: Melbourne Water, Docklands, Victoria, Australia
L. Zhang: CSIRO Land and Water, Black Mountain, Australian Capital Territory, Australia
P. Lane: School of Ecosystem and Forest Sciences, University of Melbourne, Parkville, Victoria, Australia
A. Kiem: Centre for Water, Climate and Land (CWCL), College of Engineering, Science and Environment (CESE), University of Newcastle, Newcastle, New South Wales, Australia
L. Marshall: School of Civil and Environmental Engineering, University of New South Wales, Kensington, New South Wales, Australia
L. Marshall: ARC Training Centre Data Analytics for Resources and Environments, School of Life and Environmental Sciences, The University of Sydney, Camperdown, New South Wales, Australia
A. Griebel: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, New South Wales, Australia
B. E. Medlyn: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, New South Wales, Australia
D. Ryu: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
G. Bonotto: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
C. Wasko: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
A. Ukkola: Climate Change Research Centre, University of New South Wales, Kensington, New South Wales, Australia
C. Stephens: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, New South Wales, Australia
A. Frost: Bureau of Meteorology, Sydney, New South Wales, Australia
H. Gardiya Weligamage: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
P. Saco: Centre for Water Security and Environmental Sustainability and School of Engineering, University of Newcastle, Callaghan, New South Wales, Australia
H. Zheng: CSIRO Land and Water, Black Mountain, Australian Capital Territory, Australia
F. Chiew: CSIRO Land and Water, Black Mountain, Australian Capital Territory, Australia
E. Daly: Department of Civil Engineering, Monash University, Clayton, Victoria, Australia
G. Walker: Grounded In Water, Adelaide, South Australia, Australia
R. W. Vervoort: ARC Training Centre Data Analytics for Resources and Environments, School of Life and Environmental Sciences, The University of Sydney, Camperdown, New South Wales, Australia
J. Hughes: CSIRO Land and Water, Black Mountain, Australian Capital Territory, Australia
L. Trotter: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia
B. Neal: Hydrology and Risk Consulting (HARC), Blackburn, Victoria, Australia
I. Cartwright: School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria, Australia
R. Nathan: Department of Infrastructure Engineering, The University of Melbourne, Parkville, Victoria, Australia

DOI: https://doi.org/10.5194/hess-26-6073-2022
Journal volume & issue: Vol. 26
pp. 6073 – 6120

Abstract

Read online

The Millennium Drought lasted more than a decade and is notable for causing persistent shifts in the relationship between rainfall and runoff in many southeastern Australian catchments. Research to date has successfully characterised where and when shifts occurred and explored relationships with potential drivers, but a convincing physical explanation for observed changes in catchment behaviour is still lacking. Originating from a large multi-disciplinary workshop, this paper presents and evaluates a range of hypothesised process explanations of flow response to the Millennium Drought. The hypotheses consider climatic forcing, vegetation, soil moisture dynamics, groundwater, and anthropogenic influence. The hypotheses are assessed against evidence both temporally (e.g. why was the Millennium Drought different to previous droughts?) and spatially (e.g. why did rainfall–runoff relationships shift in some catchments but not in others?). Thus, the strength of this work is a large-scale assessment of hydrologic changes and potential drivers. Of 24 hypotheses, 3 are considered plausible, 10 are considered inconsistent with evidence, and 11 are in a category in between, whereby they are plausible yet with reservations (e.g. applicable in some catchments but not others). The results point to the unprecedented length of the drought as the primary climatic driver, paired with interrelated groundwater processes, including declines in groundwater storage, altered recharge associated with vadose zone expansion, and reduced connection between subsurface and surface water processes. Other causes include increased evaporative demand and harvesting of runoff by small private dams. Finally, we discuss the need for long-term field monitoring, particularly targeting internal catchment processes and subsurface dynamics. We recommend continued investment in the understanding of hydrological shifts, particularly given their relevance to water planning under climate variability and change.

Published in Hydrology and Earth System Sciences

ISSN: 1027-5606 (Print); 1607-7938 (Online)
Publisher: Copernicus Publications
Country of publisher: Germany
LCC subjects: Technology: Environmental technology. Sanitary engineering; Geography. Anthropology. Recreation: Environmental sciences
Website: http://www.hydrology-and-earth-system-sciences.net/

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