Dr Danielle Verdon-Kidd

Low-lying, developed areas in New South Wales (NSW) are susceptible to extended periods of inundation, which cannot be attributed to tides or local synoptic conditions. This inundation is often associated with relatively small water level anomalies but is persistent enough to damage the built environment. Due to their long duration, continental shelf waves (CSWs) are one of the mechanisms of concern associated with extended coastal inundation. These waves are caused by a range of synoptic disturbances occurring along the mid-latitudes and they travel anticlockwise along the coast (in the southern hemisphere), reaching low latitudes of NSW. This study investigates the characteristics of CSWs that travel along the NSW coast, their generation and propagation mechanisms in relation to local synoptic and oceanic conditions, and their potential modulation by two major large-scale climate modes: the El Niño/Southern Oscillation and the Southern Annular Mode (SAM). We used time series of daily tidal residuals from 1994 to 2015 from nine locations along the NSW coast and used a peak over threshold approach to identify 29 waves which had an average amplitude of 0.3 m, mean period of 15 days (ranging from 8 to 20 days), and a highest occurrence in autumn and winter. The generation of CSWs is tightly coupled to the subpolar jet, the belt of westerlies, and the subtropical ridge, confirming that large-scale atmospheric circulation is a key element in the generation and propagation of CSWs. Through analyses of the inverse barometer, we found that CSWs propagate freely up to the north coast of NSW, independent of local weather conditions. We also found that CSWs are more frequent during the positive phase of SAM combined with La Niña and during neutral SAM combined with El Niño events. This study provides the longest database to date of CSWs for NSW, alongside new insights into their characteristics and timing and frequency of occurrence. Importantly, this information can be used to monitor their occurrence and forecast their impact, including the number of days taken for a wave to reach different locations along the NSW coast.

Study region Western Tasmania, southeastern Australia. Study focus We present two new tree-ring based inflow reconstructions from western Tasmania in southeastern Australia.The warm season reconstruction (Dec¿Feb) extends from 1030¿2007 CE and explains up to 42% of the variance in instrumental flow, while the cool season (JA) extends from 1550¿2007 CE and explains 27% of instrumental flow variance. Key features include an extended pluvial period in the 11th Century and a protracted dry period in ~1500CE, neither of which are represented in the DJF instrumental record. Decreasing JA flow since the 19th Century is consistent with a local sediment-based hydroclimate record. New hydrological insights for the region The reconstructions confirm that the instrumental data do not capture how protracted past low or high flow periods have been. It is therefore important to consider pre-instrumental flow data when planning for the future. The reconstructions provide new insights into regional variability through their association with the Subtropical Ridge (STR) and the Southern Annular Mode (SAM). Differing spatial signatures of the seasonal reconstructions, and their associations with season-specific impacts of STR and SAM, highlight the need for caution when considering the use of remote hydroclimate proxy records with strong seasonal signatures. The reconstructions suggest that extrapolation of seasonally defined reconstructions to represent annual flow for regions beyond the extent of their spatial footprint may be problematic.

Recent extremes of flood and drought across Australia have raised questions about the recurrence of such rare events and highlighted the importance of understanding multi-decadal climate variability. However, instrumental records over the past century are too short to adequately characterise climate variability on multi-decadal and longer timescales or robustly determine extreme event frequencies and their duration. Palaeoclimate reconstructions can provide much-needed information to help address this problem. Here, we use the 600-year hydroclimate record captured in the eastern Australian and New Zealand Drought Atlas (ANZDA) to analyse drought and pluvial frequency trends for East Australian Natural Resource Management (NRM) clusters. This partitioning of the drought atlas grid points into recognised biophysical areas (i.e. NRM clusters) revealed their differences and similarities in drought intensity and pluvial events over time. We find sustained multi-decadal periods of a wet¿dry geographic 'seesaw' between eastern to central and southern NRMs (e.g. 1550¿1600 CE and 1700¿1750 CE). In contrast, other periods reveal spatially consistent wetting (e.g. 1500¿1550 CE) or drying (e.g. 1750¿1800 CE). Emerging hot spot analysis further shows that some areas that appear naturally buffered from severe drought during the instrumental period have a greater exposure risk when the longer 600-year record is considered. These findings are particularly relevant to management plans when dealing with the impacts of climate extremes developed at regional scales. Our results demonstrate that integrating and extending instrumental records with palaeoclimate datasets will become increasingly important for developing robust and locally specific extreme event frequency information for managing water resources.

Perennial freshwater systems are valuable natural resources that provide important ecological services globally. However, in highly variable climates, such as Australia, water availability in rivers and streams can vary greatly from year to year and from decade to decade. Further, across Australia and many other regions, perennial river systems are projected to decrease because of anthropogenic climate change, placing the ecosystems they support under additional pressure. Quantifying the potential impacts of climate change on perennial freshwater systems requires robust databases of existing water features with accurate classifications. This is a challenge for rivers that display a high degree of interannual variability since the river classification can be dependent on the period of available data. In this study, we carry out a regional scale comparison of three different spatial databases commonly used in environmental and ecological assessments of perennial systems of Australia, namely Geodata, Geofabric and Water Observations from Space (WOfS). Focusing on the southern Murray Darling Basin (MDB), due to its national and international significance and its highly variable flow regimes, we show that no single spatial database is reliable by itself in terms of perennial water classification, with notable differences likely arising from variations in the periods analysed and methods used to classify the systems. Further, an analysis of high-quality gauged streamflow data (with approximately 40-year daily records) for four sub-catchments, and long-term simulation data (>100 years) for two sub-catchments in the lower MDB, confirm that flow persistence can be non-stationary through time, with some 'perennial' systems exhibiting sustained periods of cease to flow (i.e. becoming non-perennial) during prolonged droughts. This study demonstrates that due consideration is required in developing baseline classification of perennial freshwater systems for assessing future changes and measuring adaptive capacity.

Tropical cyclones (TCs) impact the economy, properties, lives and infrastructure of island nations and territories of the southwest Pacific (SWP), accounting for three in four regional disasters each year. To increase the resilience of the SWP to the destructive impacts of TCs, improved TC track forecasts are needed since a high degree of uncertainty exists around the likely path a TC will take in this region post-formation. This requires better comprehension of the factors contributing to TC track variability occurring at different timescales. Therefore, we examine the modulating impact of key Indo-Pacific climate drivers: the El Niño-Southern Oscillation (ENSO), Interdecadal Pacific Oscillation (IPO), Southern Annular Mode (SAM) and the Indian Ocean Dipole (IOD), on SWP TC track variability. We present new insights into the spatial (i.e. prevailing trajectories) and temporal (i.e. track length, average speed and duration) components of TC tracks, being modulated by both individual and combined climate modes. Overall, TC tracks tend to shift northeast during El Niño, IPO positive, IOD east positive and/or SAM negative phases (with a southwest shift observed during the opposite climate phases). Further, we show that when two of these climate modes are in their positive phase (e.g. El Niño with the positive phases of IPO or eastern pole of IOD and SAM), TC track length and average speed are enhanced. However, for cases where either one (e.g. El Niño/negative phase of IPO and IOD east) or two (La Niña/negative phase of IPO, IOD east and SAM) climate modes were in the negative phase, an increase in TC track duration was observed. The findings of this study may be used to improve TC forecasting and better quantify TC-related risks.

The development of high-resolution terrestrial palaeoclimate records in Australia is hindered by the scarcity of tree species suitable for conventional dendrochronology. However, novel analytical techniques have made it possible to obtain climate information from tree species that do not reliably form annual growth rings. In this paper we assess the potential of stable carbon and oxygen isotopes in the xylem wood of grey mangroves (Avicennia marina (Forssk.) Vierh.) as hydroclimate proxies for eastern Australia. Bomb-pulse radiocarbon dating and simple age models were used to estimate the age of the growth layers in radial sequence in stems from four grey mangrove trees in two adjacent estuaries in New South Wales, Australia. Stable isotope data measured from the xylem wood of the four stems were composited to yield mean d18O and d13C series for the 1962¿2016 period. Significant negative Spearman correlations were found between d18O and rainfall, sea level, instrumental Palmer Drought Severity Index (scPDSI) and the El Niño Southern Oscillation (ENSO), while d13C was positively correlated with temperature, vapour pressure and evapotranspiration. The results demonstrate that stable oxygen isotopes in grey mangroves have the potential to yield valuable information about pre-instrumental hydroclimate. Grey mangroves can survive with intact centres for an estimate of >250 years based on observed growth rates, are widespread along northern Australian and tropical coastlines and could provide important information regarding pre-instrumental climate in regions currently lacking high-resolution (i.e., near annual) centennial scale climate proxy records.

The factors determining the spatial distribution of soil organic carbon (SOC) at large-scales closely align with bioclimate regions; reflecting climate, ecosystem and soil properties. Recent studies of the Köppen-Geiger climate zones of Australia have highlighted an extension of the hot, arid, steppe environment from central Australia into the southeast (SE) under future climate change scenarios (2071¿2100 under RCP 8.5). As SOC concentrations are highest in Australia's SE, it is important the effect of this shift is quantified. This study assesses this and how changes in the factors that control SOC formation may alter SOC concentrations. Field measured SOC concentrations were compared to current climate, soil, topography, vegetation, and soil erosion variables for 12 grassland sites from SE to NW Australia. SOC concentrations ranged from 0.39% in northwest (NW) and Central Australia to as high as 6.88% in the SE. Using regression analyses; temperature, elevation and Normalised Difference Vegetation Index were found to be the only significant drivers (a = 0.95) of SOC across the sites. Partial correlation analyses then identified temperature, elevation and clay content as imparting a significant effect on the relationships between SOC and water availability variables. This indicates that an extension of the arid environment into SE Australia may lead to a decrease in SOC (up to 1.12%), as mean annual temperature exceeds threshold values that limit SOC concentration. This is significant as the majority of Australia's SOC is stored in this area and these environments exert a strong influence on global carbon cycling.

Local government organisations in coastal Australia have historically commissioned studies aimed at understanding risks in their locality to future sea level rise as a starting point for developing adaptation strategies to climate change. Therefore, the success of the overall adaptation activities of local government are strongly influenced by the way those initial risk studies are scoped and conducted, and how the outputs of those studies underpin subsequent adaptation planning activities within the organization. Mainstreaming of adaptation planning activities within local government is critical in terms of getting stakeholder support and required resources for its implementation. This paper analyses a sample of these coastal risk assessment studies across seven states and territories in Australia, with an aim to critically investigate the current state of practice among coastal local governments. First, we develop a typology of studies that have been undertaken by or for practitioners to understand coastal climate change risks, and discuss the applicability of the studies within the policy-making context of local government. Second, we identify a set of sample studies from the 'grey literature' through a systematic process and investigate to what extent they adhere to best practice risk management guidelines and principles, such as ISO31000. Third, we interview stakeholders from top performing studies to identify how/if the risk studies helped their organization in progressing their adaptation planning. We find that there is a significant inconsistency among terminologies in the coastal climate change risk assessment unpublished literature as studies use "risk", vulnerability" and "hazard" concepts interchangeably despite their separate objectives and aims. Most studies perform poorly in evaluating risk against broader organizational criteria. Subsequently, it is difficult to integrate the findings of such studies into a broader organizational risk register, limiting opportunities for identified coastal climate change risks to be integrated into councils' long-term strategic decision making. Conversely, the follow up interviews of studies that performed well in scoping and consultation in our assessment demonstrate that these aspects were beneficial to stakeholders in terms of informing adaptation planning. Importantly, the findings presented in this paper confirm the need for a consistent risk assessment approach for local councils in the coastal zone to underpin successful adaptation planning. This is a critical issue, not only for Australia, but for local government organisations globally given that sea level rise is a projected threat for all populated coastal regions worldwide.

The Monsoonal North West (MNW) region of Australia faces a number of challenges adapting to anthropogenic climate change. These have the potential to impact on a range of industries, including agricultural, pastoral, mining and tourism. However future changes to rainfall regimes remain uncertain due to the inability of Global Climate Models to adequately capture the tropical weather/climate processes that are known to be important for this region. Compounding this is the brevity of the instrumental rainfall record for the MNW, which is unlikely to represent the full range of climatic variability. One avenue for addressing this issue (the focus of this paper) is to identify sources of paleoclimate information that can be used to reconstruct a plausible pre-instrumental rainfall history for the MNW. Adopting this approach we find that, even in the absence of local sources of paleoclimate data at a suitable temporal resolution, remote paleoclimate records can resolve 25% of the annual variability observed in the instrumental rainfall record. Importantly, the 507-year rainfall reconstruction developed using the remote proxies displays longer and more intense wet and dry periods than observed during the most recent ~ 100 years. For example, the maximum number of consecutive years of below (above) average rainfall is 90% (40%) higher in the rainfall reconstruction than during the instrumental period. Further, implications for flood and drought risk are studied via a simple GR1A rainfall runoff model, which again highlights the likelihood of extremes greater than that observed in the limited instrumental record, consistent with previous paleoclimate studies elsewhere in Australia. Importantly, this research can assist in informing climate related risks to infrastructure, agriculture and mining, and the method can readily be applied to other regions in the MNW and beyond.

Recent efforts to understand tropical cyclone (TC) activity in the southwest Pacific (SWP) have led to the development of numerous TC databases. The methods used to compile each database vary and are based on data from different meteorological centres, standalone TC databases and archived synoptic charts. Therefore the aims of this study are to (i) provide a spatiooral comparison of three TC best-track (BT) databases and explore any differences between them (and any associated implications) and (ii) investigate whether there are any spatial, temporal or statistical differences between pre-satellite (1945-1969), postsatellite (1970-2011) and post-geostationary satellite (1982-2011) era TC data given the changing observational technologies with time. To achieve this, we compare three besttrack TC databases for the SWP region (0-35° S, 135° E-120° W) from 1945 to 2011: the Joint TyphoonWarning Center (JTWC), the International Best Track Archive for Climate Stewardship (IBTrACS) and the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC). The results of this study suggest that SPEArTC is the most complete repository of TCs for the SWP region. In particular, we show that the SPEArTC database includes a number of additional TCs, not included in either the JTWC or IBTrACS database. These SPEArTC events do occur under environmental conditions conducive to tropical cyclogenesis (TC genesis), including anomalously negative 700 hPa vorticity (VORT), anomalously negative vertical shear of zonal winds (VSZW), anomalously negative 700 hPa geopotential height (GPH), cyclonic (absolute) 700 hPa winds and low values of absolute vertical wind shear (EVWS). Further, while changes in observational technologies from 1945 have undoubtedly improved our ability to detect and monitor TCs, we show that the number of TCs detected prior to the satellite era (1945-1969) are not statistically different to those in the postsatellite era (post-1970). Although data from pre-satellite and pre-geostationary satellite periods are currently inadequate for investigating TC intensity, this study suggests that SPEArTC data (from 1945) may be used to investigate longterm variability of TC counts and TC genesis locations.

The destruction caused by tropical cyclone (TC) Pam in March 2015 is considered one of the worst natural disasters in the history of Vanuatu. It has highlighted the need for a better understanding of TC impacts and adaptation in the Southwest Pacific (SWP) region. Therefore, the key aims of this study are to (i) understand local perceptions of TC activity, (ii) investigate impacts of TC activity and (iii) uncover adaptation strategies used to offset the impacts of TCs. To address these aims, a survey (with 130 participants from urban areas) was conducted across three SWP small island states (SISs): Fiji, Vanuatu and Tonga (FVT). It was found that respondents generally had a high level of risk perception and awareness of TCs and the associated physical impacts, but lacked an understanding of the underlying weather conditions. Responses highlighted that current methods of adaptation generally occur at the local level, immediately prior to a TC event (preparation of property, gathering of food, finding a safe place to shelter). However higher level adaptation measures (such as the modification to building structures) may reduce vulnerability further. Finally, we discuss the potential of utilising weather-related traditional knowledge and non-traditional knowledge of empirical and climate-model-based weather forecasts to improve TC outlooks, which would ultimately reduce vulnerability and increase adaptive capacity. Importantly, lessons learned from this study may result in the modification and/or development of existing adaptation strategies.

Rainfall intensity-frequency-duration (IFD) relationships are commonly required for the design and planning of water supply and management systems around the world. Currently, IFD information is based on the "stationary climate assumption" that weather at any point in time will vary randomly and that the underlying climate statistics (including both averages and extremes) will remain constant irrespective of the period of record. However, the validity of this assumption has been questioned over the last 15 years, particularly in Australia, following an improved understanding of the significant impact of climate variability and change occurring on interannual to multidecadal timescales. This paper provides evidence of regime shifts in annual maximum rainfall time series (between 1913-2010) using 96 daily rainfall stations and 66 sub-daily rainfall stations across Australia. Furthermore, the effect of these regime shifts on the resulting IFD estimates are explored for three long-term (1913-2010) sub-daily rainfall records (Brisbane, Sydney, and Melbourne) utilizing insights into multidecadal climate variability. It is demonstrated that IFD relationships may under-or over-estimate the design rainfall depending on the length and time period spanned by the rainfall data used to develop the IFD information. It is recommended that regime shifts in annual maximum rainfall be explicitly considered and appropriately treated in the ongoing revisions of the Engineers Australia guide to estimating and utilizing IFD information, Australian Rainfall and Runoff (ARR), and that clear guidance needs to be provided on how to deal with the issue of regime shifts in extreme events (irrespective of whether this is due to natural or anthropogenic climate change). The findings of our study also have important implications for other regions of the world that exhibit considerable hydroclimatic variability and where IFD information is based on relatively short data sets.

There is a recognised gap between what climate science can currently provide and what end users of that information require to make robust adaptation decisions about their climate-related risks. This issue has been identified as a major barrier to successful climate change adaptation outcomes and is emphasised within the water resource management and agricultural sectors because of high uncertainty surrounding precipitation projections. This paper details the outcomes of a survey and workshop aimed at better understanding this gap. To bridge the gap, it is recommended that communication and packaging of climate information be improved via a formalised 'knowledge broker'. It is also suggested that a 'terms of reference' for key climate change-related terms be developed and agreed upon by both climate science providers and end users to reduce the misuse of terminology and subsequent confusion. Further, it is recommended that additional research be conducted into natural variability and baseline risk to provide a realistic background on which climate change projections and associated uncertainties are assessed. Finally, for successful climate change adaptation, new tools and methods are needed that deal explicitly with end user needs and the practical limitations end users face (e.g. time, funding, human resources, politics) when attempting to make robust decisions under climate change-related uncertainty.

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. © Author(s) 2014.

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. © 2014 Author(s).

Worldwide, severe droughts have extensive environmental impacts, such as declined crop yield and livestock production, inadequate water supply and elevated risk of bushfires. Additionally, dealing with drought breaking floods adds significant strain to society and the economy, particularly when businesses and communities are not prepared. Increasing vulnerability to droughts with reduced per capita water storage, particularly in semiarid regions such as the Murray Darling Basin (MDB), Australia, underscores the need for predictive understanding of drought. However, at present, useful forecasts of persistent drought or drought breaking conditions are not yet achievable due to our incomplete understanding of the controls on drought extent and duration. Therefore, to better coordinate drought planning and drought relief activities, it is imperative to understand the factors affecting drought initialisation and cessation. In this paper, the spatial and temporal characteristics of historical droughts (both meteorological and hydrological) that have affected in the MDB are examined. It is shown that historically, drought has varied spatially across the MDB, with significant differences (in terms of timing and severity of drought) between the Upper and Lower MDB. It is also shown that meteorological droughts tend to develop gradually over the MDB, while hydrological drought develops much more rapidly. Further, it is shown that climate drivers of Pacific origin (i.e. El Nino/Southern Oscillation and Interdecadal Pacific Oscillation) play a significant role in drought initiation for the majority of historical droughts since 1900 and, for northern MDB droughts, anomalously cool SSTs off the Northwest of Australia precede all but one of the historical droughts identified. Undoubtedly the reoccurrence of drought places a major strain on the agricultural and water resource management sectors and imposes major economic and social losses. However, with improved knowledge of the climate mechanisms controlling the onset of drought periods, alleviation of the effects may be achieved through improved forecasts and management practices designed specifically to deal with such events.