Danielle C. Verdon-Kidd

Quantifying Drought Risk in a Nonstationary Climate

Abstract Water management in Australia has traditionally been carried out on the assumption that the historical record of rainfall, evaporation, streamflow, and recharge is representative of current and future climatic conditions. However, in many circumstances, this does not adequately address the potential risks to supply security for towns, industry, irrigators, and the environment. This is because the Australian climate varies markedly due to natural cycles that operate over periods of several years to several decades. There is also serious concern about how anthropogenic climate change may exacerbate drought risk in the future. In this paper, the frequency and severity of droughts are analyzed during a range of “climate states” (e.g., different phases of the Pacific, Indian, and/or Southern Oceans) to demonstrate that drought risk varies markedly over interannual through to multidecadal time scales. Importantly, by accounting for climate variability and change on multitemporal scales (e.g., interdeca...

Climatic drivers of Victorian streamflow: Is ENSO the dominant influence?

Abstract This study investigates the relationship between Victorian streamflow and a number of large-scale climate drivers, including the El Niño/Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM). It is found that identifying a “dominant” climate driver, at least in the case of Victorian streamflow, is not a clear cut exercise. Importantly, it is shown that ENSO alone explains only a very small proportion of Victorian streamflow variability, particularly in autumn (a critical time in Victoria’s hydrological and water resources management cycle). This is a crucial insight given that most seasonal forecasting schemes currently used in Australia are based primarily on ENSO relationships. The results presented here show that stratification of Victorian streamflow according to multiple large-scale climate drivers, and antecedent catchment conditions, provides significantly differing streamflow distributions. Therefore, incorporation of (a) antecedent catchment conditions into the forecasting framework and (b) improved insights into the multiple interactions between all relevant large-scale (and local) climate drivers should improve seasonal streamflow forecasting ability.

The importance of understanding drivers of hydroclimatic variability for robust flood risk planning in the coastal zone

Abstract Previous work has established that the risk of climate related emergencies (eg. floods, droughts, bushfires, etc.) in Australia, and many other parts of the world, is non-stationary. That is, the chance of an extreme climatic event occurring is not the same from one year to the next and is in fact dependent on the state of the various ocean-atmospheric phenomena that are responsible for Australia’s hydroclimatic variability. This previous work demonstrated how, on average for New South Wales, the probability of a flood occurring that is equal in magnitude to the 1-in-100 year flood is about five times greater during La Niña events compared to all other years and 12 times greater during a La Niña event that occurs during the negative phase of the Inter-decadal Pacific Oscillation compared to all other years. This work has recently been extended to focus specifically on urban coastal areas where it has been found that the non-stationarity of flood risk is even further enhanced when compared to the non-coastal catchments. Also investigated is whether this non-stationarity of flood risk is due to non-stationarity of antecedent conditions or non-stationarity of extreme daily and sub-daily rainfall events, with the finding being that both are important. This is contrary to recent studies that claim there is no evidence of non-stationarity in extreme daily and sub-daily rainfall across Australia. The implications of these results are significant given the large populations and infrastructure investment along the eastern seaboard and also timely given current updates to Engineers Australia’s Australian Rainfall and Runoff: A Guide to Flood Estimation, the standard for flood estimation in Australia.

A paleoclimate rainfall reconstruction in the Murray‐Darling Basin (MDB), Australia: 2. Assessing hydroclimatic risk using paleoclimate records of wet and dry epochs

Estimates of hydrological risk are crucial to enable adequate planning and preparation for extreme events. However, the accurate estimation of hydrological risk is hampered by relatively short instrumental records in many parts of the world. Information derived from climate-sensitive paleoclimate proxies provide an opportunity to resolve hydroclimatic variability, but many regions, such as Australias Murray-Darling Basin (MDB), currently lack the suitable in situ proxies necessary to do this. Here, new MDB rainfall reconstructions are presented based on a novel method using paleoclimate rainfall proxies in the Australasian region spanning from 749 BCE to 1980 CE. Our results emphasize the need to develop additional reconstructions and, with the companion paper, demonstrate how this information can be used to benefit water resource management. This study shows that prior to the 20th century both dry and wet epochs have persisted for longer periods than observed in the instrumental record – with the probability of both dry and wet periods exceeding a decade at least 10 times more likely prior to 1883 than suggested by the instrumental records. Some reconstructed rainfalls exceeded the instrumental range (i.e. drier dry epochs and wetter wet spells) despite a systematic underestimation of extremes due to a combination of proxy quality and model bias. Importantly, the results demonstrate that the instrumental record does not cover the full range of hydroclimatic variability possible in the MDB. Therefore hydroclimatic risk assessments based on the instrumental record likely underestimate, or at least misinterpret, the frequency, duration and magnitude of wet and dry epochs. This article is protected by copyright. All rights reserved.

Broadening the Spatial Applicability of Paleoclimate Information—A Case Study for the Murray–Darling Basin, Australia

Recent advances in the collection and analysis of paleoclimate data have provided significant insights into preinstrumental environmental events and processes, enabling a greater understanding of long-term environmental change and associated hydroclimatic risks. Unfortunately, it is often the case that there is a dearth of readily available paleoclimate data from regions where such insights and long-term data are most needed. The Murray‐Darling basin (MDB), known as Australia’s ‘‘food bowl,’’ is an example of such a region where currently there are very limited in situ paleoclimate data available. While previous studies have utilized paleoclimate proxy records of large-scale climate mechanisms to infer preinstrumental MDB hydroclimatic variability, there is a lack of studies that utilize Australian terrestrial proxy records to garner similar information. Given the immediate need for improved understanding of MDB hydroclimatic variability, this paper identifies key locations in Australia where existing and as yet unrealized paleoclimate records will be most useful in reconstructing such information. To identify these key locations, rainfall relationships between MDB and non-MDB locations were explored through correlations and principal component analysis. An objective analysisusing optimalinterpolation was thenused to pinpoint the most strategic locations to further developproxyrecordsandgaininsightsintothebenefitsofobtainingthis additionalinformation.Thefindings reveal that there is potential for the future assembly of high-resolution paleoclimate records in Australia capable of informing MDB rainfall variability, in particular southeast Australia and central-northern Australia. This study highlights the need for further investment in the development of these potential proxy sources to subsequently enable improved assessments of long-term hydroclimatic risks.

A paleoclimate rainfall reconstruction in the Murray‐Darling Basin (MDB), Australia: 1. Evaluation of different paleoclimate archives, rainfall networks, and reconstruction techniques

From ∼1997 to 2009 the Murray-Darling Basin (MDB), Australias largest water catchment and reputed “food bowl,” experienced a severe drought termed the “Millennium Drought” or “Big Dry” followed by devastating floods in the austral summers of 2010/2011, 2011/2012, and 2012/2013. The magnitude and severity of these extreme events highlight the limitations associated with assessing hydroclimatic risk based on relatively short instrumental records (∼100 years). An option for extending hydroclimatic records is through the use of paleoclimate records. However, there are few in situ proxies of rainfall or streamflow suitable for assessing hydroclimatic risk in Australia and none are available in the MDB. In this paper, available paleoclimate records are reviewed and those of suitable quality for hydroclimatic risk assessments are used to develop preinstrumental information for the MDB. Three different paleoclimate reconstruction techniques are assessed using two instrumental rainfall networks: (1) corresponding to rainfall at locations where rainfall-sensitive Australian paleoclimate archives currently exist and (2) corresponding to rainfall at locations identified as being optimal for explaining MDB rainfall variability. It is shown that the optimized rainfall network results in a more accurate model of MDB rainfall compared to reconstructions based on rainfall at locations where paleoclimate rainfall proxies currently exist. This highlights the importance of first identifying key locations where existing and as yet unrealized paleoclimate records will be most useful in characterizing variability. These results give crucial insight as to where future investment and research into developing paleoclimate proxies for Australia could be most beneficial, with respect to better understanding instrumental, preinstrumental and potential future variability in the MDB.

East Coast Lows and the Pasha Bulker storm—lessons learned nine years on

East Coast Lows (ECLs) are intense low pressure systems that form several times a year off the east coast of Australia. When these systems occur close to land they can cause major damage to infrastructure and communities due to gale force winds, intense rainfall, storm surge and coastal erosion. In June 2007, Newcastle and Central Coast regions of New South Wales (NSW) experienced severe weather and subsequent flash flooding. The ‘Pasha Bulker’ storm, as it has become known, was one of the most significant meteorological events in Australia’s history, with large economic losses and social disruption due to the loss of critical infrastructure. This paper provides background information on the meteorology of the event, the impact of the Pasha Bulker storm and a discussion of the lessons learned from the event and subsequent adaptation strategies employed. The paper also provides important reflections, at both regional and national level, on the Pasha Bulker storm and other similar storm events. Lessons for all levels of government and community groups are discussed, including preparedness before the event, actions during the event, and recovery processes post-event. From this, recommendations and conclusions are made on actions and strategies to increase adaptive capacity and resilience to extreme weather events like ECLs.