495 research outputs found
Robust optimisation of urban drought security for an uncertain climate
Abstract
Recent experience with drought and a shifting climate has highlighted the vulnerability of urban water supplies to ârunning out of waterâ in Perth, south-east Queensland, Sydney, Melbourne and Adelaide and has triggered major investment in water source infrastructure which ultimately will run into tens of billions of dollars. With the prospect of continuing population growth in major cities, the provision of acceptable drought security will become more pressing particularly if the future climate becomes drier.
Decision makers need to deal with significant uncertainty about future climate and population. In particular the science of climate change is such that the accuracy of model predictions of future climate is limited by fundamental irreducible uncertainties. It would be unwise to unduly rely on projections made by climate models and prudent to favour solutions that are robust across a range of possible climate futures.
This study presents and demonstrates a methodology that addresses the problem of finding âgoodâ solutions for urban bulk water systems in the presence of deep uncertainty about future climate. The methodology involves three key steps: 1) Build a simulation model of the bulk water system; 2) Construct replicates of future climate that reproduce natural variability seen in the instrumental record and that reflect a plausible range of future climates; and 3) Use multi-objective optimisation to efficiently search through potentially trillions of solutions to identify a set of âgoodâ solutions that optimally trade-off expected performance against robustness or sensitivity of performance over the range of future climates.
A case study based on the Lower Hunter in New South Wales demonstrates the methodology. It is important to note that the case study does not consider the full suite of options and objectives; preliminary information on plausible options has been generalised for demonstration purposes and therefore its results should only be used in the context of evaluating the methodology. âDryâ and âwetâ climate scenarios that represent the likely span of climate in 2070 based on the A1F1 emissions scenario were constructed. Using the WATHNET5 model, a simulation model of the Lower Hunter was constructed and validated. The search for âgoodâ solutions was conducted by minimizing two criteria, 1) the expected present worth cost of capital and operational costs and social costs due to restrictions and emergency rationing, and 2) the difference in present worth cost between the âdryâ and âwetâ 2070 climate scenarios. The constraint was imposed that solutions must be able to supply (reduced) demand in the worst drought. Two demand scenarios were considered, â1.28 x current demandâ representing expected consumption in 2060 and â2 x current demandâ representing a highly stressed system. The optimisation considered a representative range of options including desalination, new surface water sources, demand substitution using rainwater tanks, drought contingency measures and operating rules.
It was found the sensitivity of solutions to uncertainty about future climate varied considerably. For the â1.28 x demandâ scenario there was limited sensitivity to the climate scenarios resulting in a narrow range of trade-offs. In contrast, for the â2 x demandâ scenario, the trade-off between expected present worth cost and robustness was considerable. The main policy implication is that (possibly large) uncertainty about future climate may not necessarily produce significantly different performance trajectories. The sensitivity is determined not only by differences between climate scenarios but also by other external stresses imposed on the system such as population growth and by constraints on the available options to secure the system against drought.
Recent experience with drought and a shifting climate has highlighted the vulnerability of urban water supplies to ârunning out of waterâ in Perth, south-east Queensland, Sydney, Melbourne and Adelaide and has triggered major investment in water source infrastructure which ultimately will run into tens of billions of dollars. With the prospect of continuing population growth in major cities, the provision of acceptable drought security will become more pressing particularly if the future climate becomes drier.
Decision makers need to deal with significant uncertainty about future climate and population. In particular the science of climate change is such that the accuracy of model predictions of future climate is limited by fundamental irreducible uncertainties. It would be unwise to unduly rely on projections made by climate models and prudent to favour solutions that are robust across a range of possible climate futures.
This study presents and demonstrates a methodology that addresses the problem of finding âgoodâ solutions for urban bulk water systems in the presence of deep uncertainty about future climate. The methodology involves three key steps: 1) Build a simulation model of the bulk water system; 2) Construct replicates of future climate that reproduce natural variability seen in the instrumental record and that reflect a plausible range of future climates; and 3) Use multi-objective optimisation to efficiently search through potentially trillions of solutions to identify a set of âgoodâ solutions that optimally trade-off expected performance against robustness or sensitivity of performance over the range of future climates.
A case study based on the Lower Hunter in New South Wales demonstrates the methodology. It is important to note that the case study does not consider the full suite of options and objectives; preliminary information on plausible options has been generalised for demonstration purposes and therefore its results should only be used in the context of evaluating the methodology. âDryâ and âwetâ climate scenarios that represent the likely span of climate in 2070 based on the A1F1 emissions scenario were constructed. Using the WATHNET5 model, a simulation model of the Lower Hunter was constructed and validated. The search for âgoodâ solutions was conducted by minimizing two criteria, 1) the expected present worth cost of capital and operational costs and social costs due to restrictions and emergency rationing, and 2) the difference in present worth cost between the âdryâ and âwetâ 2070 climate scenarios. The constraint was imposed that solutions must be able to supply (reduced) demand in the worst drought. Two demand scenarios were considered, â1.28 x current demandâ representing expected consumption in 2060 and â2 x current demandâ representing a highly stressed system. The optimisation considered a representative range of options including desalination, new surface water sources, demand substitution using rainwater tanks, drought contingency measures and operating rules.
It was found the sensitivity of solutions to uncertainty about future climate varied considerably. For the â1.28 x demandâ scenario there was limited sensitivity to the climate scenarios resulting in a narrow range of trade-offs. In contrast, for the â2 x demandâ scenario, the trade-off between expected present worth cost and robustness was considerable. The main policy implication is that (possibly large) uncertainty about future climate may not necessarily produce significantly different performance trajectories. The sensitivity is determined not only by differences between climate scenarios but also by other external stresses imposed on the system such as population growth and by constraints on the available options to secure the system against drought.
Please cite this report as:
Mortazavi, M, Kuczera, G, Kiem, AS, Henley, B, Berghout, B,Turner, E, 2013 Robust optimisation of urban drought security for an uncertain climate. National Climate Change Adaptation Research Facility, Gold Coast, pp. 74
Synchronicity of historical dry spells in the Southern Hemisphere
A shift in climate occurred during the mid-1970s that affected the
hydroclimate of the Southern Hemisphere resulting in drying trends across
continental regions including Australia, New Zealand and southern and western
Africa. There is also anecdotal evidence of other periods of climatic
synchronicity in the Southern Hemisphere (e.g., the 1920s and 1940s),
indicating that the mid-1970s event may not be anomalous. This paper
identifies periods within the last ~120 years using statistical
analysis where dry spells (in terms of annual to multi-decadal rainfall
deficiencies) have coincided across the continental Southern Hemisphere in
order to characterize temporal consistency. It is shown that synchronicity of
dry spells is (a) most likely common over the last 120 years and (b)
associated with changes in the large-scale climate modes of the Pacific,
Indian and Southern Oceans. Importantly, the findings presented in this paper
have marked implications for drought management and drought forecasting
studies in the Southern Hemisphere
Interacting Dipoles from Matrix Formulation of Noncommutative Gauge Theories
We study the IR behavior of noncommutative gauge theory in the matrix
formulation. We find that in this approach, the nature of the UV/IR mixing is
easily understood, which allows us to perform a reliable calculation of the
quantum effective action for the long wavelength modes of the noncommutative
gauge field. At one loop, we find that our description is weakly coupled only
in the supersymmetric theory. At two loops, we find non-trivial interaction
terms suggestive of dipole degrees of freedom. These dipoles exhibit a channel
duality reminiscent of string theory.Comment: LaTeX 11 pages, 4 figures; v.2 minor changes and some references
added; v.3 many more technical details added and significantly different
presentation, use REVTeX 4, to appear in PR
U(N) Instantons on N=1/2 superspace -- exact solution & geometry of moduli space
We construct the exact solution of one (anti)instanton in N=1/2 super
Yang-Mills theory defined on non(anti)commutative superspace. We first identify
N = 1/2 superconformal invariance as maximal spacetime symmetry. For gauge
group U(2), SU(2) part of the solution is given by the standard
(anti)instanton, but U(1) field strength also turns out nonzero. The solution
is SO(4) rotationally symmetric. For gauge group U(N), in contrast to the U(2)
case, we show that the entire U(N) part of the solution is deformed by
non(anti)commutativity and fermion zero-modes. The solution is no longer
rotationally symmetric; it is polarized into an axially symmetric configuration
because of the underlying non(anti)commutativity. We compute the `information
metric' of one (anti) instanton. We find that moduli space geometry is deformed
from hyperbolic space (Euclidean anti-de Sitter space) in a way anticipated
from reduced spacetime symmetry. Remarkably, the volume measure of the moduli
space turns out to be independent of the non(anti)commutativity. Implications
to D-branes in Ramond- Ramond flux background and Maldacena's gauge-gravity
correspondence are discussed.Comment: 39 pages, 3 figures, JHEP style; v2. typos corrected + a paragraph
adde
Introduction to the special issue : historical and projected climatic changes to Australian natural hazards
Australiaâs size and varied climates mean that it is affected by a range of weather-related natural hazards, including tropical and extra-tropical storms and associated extreme wind and hail, coastal and inland floods, heatwaves and bushfires. These hazards cause multiple human and environmental impacts, and collectively account for 93 % of Australian insured losses (Schuster 2013). In addition, droughtâoften treated distinctly from other hazards due to its more gradual onsetâcan cause substantial reductions in agricultural productivity, and places stress on municipal and industrial water resources and natural ecosystems. Evidence is building that the frequency and cost of natural hazards are increasing both in Australia (Insurance Council of Australia 2013; Schuster 2013) and globally (Munich Re 2014). However, understanding the cause of these changes has proved to be difficult, with increases in reporting rates (Munich Re 2014), changes in societal exposure and vulnerability (Bouwer 2011; Neumayer and Barthel 2011) and anthropogenic climate change (IPCC 2013) all potentially playing a role in explaining the observed changes. Yet although the potential causes are many, correct attribution of the observed changes is necessary in order to identify appropriate policy responses, and to predict how the frequency and severity of natural hazards might change in the future. This Special Issue focuses on the specific role of large-scale climatic changes on the observed and future incidence of Australian natural hazards. The Special Issue is divided into seven papers, each covering a major class of climate-influenced natural hazard: floods, drought, storms (including wind and hail), coastal extremes, bushfires, heatwaves and frost. The work was initiated by the Working Group on Trends and Extremes from the Australian Water and Energy Exchanges (OzEWEX) initiative, which is a regional hydroclimate project run under the auspices of the Global Energy and Water Exchanges (GEWEX) initiative
Infinite Lorentz boost along the M-theory circle and non-asymptotically flat solutions in supergravities
Certain non-asymptotically flat but supersymmetric classical solution of the
type IIA supergravity can be interpreted as the infinitely-boosted version of
the D-particle solution along the M-theory circle. By a chain of T-dual
transformations, this analysis also applies to yield non-asymptotically flat
solutions from the asymptotically flat and (non)-extremal solutions with
intersecting D-strings and D five-branes of the type IIB supergravity
compactified on a five-torus. Under S-duality, the non-asymptotically flat
solutions in this context can in particular be used to describe the
(1+1)-dimensional CGHS type black holes via spontaneous compactifications.Comment: 14 pages, Revte
Links between the Big Dry in Australia and hemispheric multi-decadal climate variability – implications for water resource management
Southeast Australia (SEA) experienced a protracted drought during the
mid-1990s until early 2010 (known as the Big Dry or Millennium Drought) that
resulted in serious environmental, social and economic effects. This paper
analyses a range of historical climate data sets to place the recent drought
into context in terms of Southern Hemisphere inter-annual to multi-decadal
hydroclimatic variability. The findings indicate that the recent Big Dry in
SEA is in fact linked to the widespread Southern Hemisphere climate shift
towards drier conditions that began in the mid-1970s. However, it is shown
that this link is masked because the large-scale climate drivers responsible
for drying in other regions of the mid-latitudes since the mid-1970s did not
have the same effect on SEA during the mid- to late 1980s and early 1990s.
More specifically, smaller-scale synoptic processes resulted in elevated
autumn and winter rainfall (a crucial period for SEA hydrology) during the
mid- to late 1980s and early 1990s, which punctuated the longer-term drying.
From the mid-1990s to 2010 the frequency of the synoptic processes associated
with elevated autumn/winter rainfall decreased, resulting in a return to
drier than average conditions and the onset of the Big Dry. The findings
presented in this paper have marked implications for water management and
climate attribution studies in SEA, in particular for understanding and
dealing with "baseline" (i.e. current) hydroclimatic risks
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