Anthony S. Kiem

Multi-decadal variability of flood risk

Recent research has highlighted the persistence of multi-decadal epochs of enhanced/reduced flood risk across New South Wales (NSW), Australia. Recent climatological studies have also revealed multi-decadal variability in the modulation of the magnitude of El Nin椀/Southern Oscillation (ENSO) impacts. In this paper, the variability of flood risk across NSW is analysed with respect to the observed modulation of ENSO event magnitude. This is achieved through the use of a simple index of regional flood risk. The results indicate that cold ENSO events (La Nin和) are the dominant drivers of elevated flood risk. An analysis of multidecadal modulation of flood risk is achieved using the interdecadal Pacific Oscillation (IPO) index. The analysis reveals that IPO modulation of ENSO events leads to multi-decadal epochs of elevated flood risk, however this modulation appears to affect not only the magnitude of individual ENSO events, but also the frequency of their occurrence. This dual modulation of ENSO processes has the effect of reducing and elevating flood risk on multi-decadal timescales. These results have marked implications for achieving robust flood frequency analysis as well as providing a strong example of the role of natural climate variability.

On the identification of ENSO-induced rainfall and runoff variability: a comparison of methods and indices

Abstract It is known that the El Niño Southern Oscillation (ENSO) phenomenon induces marked climate variability across many parts of the world. However, in seeking useful relationships between ENSO and climate, several indices are available. In addition to the choice of index, previous studies assessing ENSO effects have employed a range of different methods to classify periods as El Niño, La Niña or Neutral. It is therefore clear that significant subjectivity exists in the adoption of ENSO classification schemes. In this study, several ENSO classification methods are applied to a range of ENSO indices. Each method-index combination is investigated to determine which provides the strongest relationship with rainfall and runoff in the Williams River catchment, New South Wales, Australia. The results demonstrate substantial differences between the methods and indices. The Multivariate ENSO Index (or MEI) is found to provide the best classification irrespective of method. The potential for forecasting ENSO-related effects on rainfall, runoff and river abstractions is then investigated. A “rise rule” to account for dynamic ENSO trends is also assessed. Strong relationships were found to exist with runoff (rainfall) up to nine (eight) months in advance of the Summer/autumn period. Implications for improved forecasting of potential river abstractions are apparent.

Multi-decadal variability of forest fire risk - eastern Australia

This study investigates the influence that the El Nino/Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO) have on long term daily weather conditions pertinent to high forest fire danger in New South Wales, Australia. Using historical meteorological data for 22 weather stations to compute the daily value of McArthur’s Forest Fire Danger Index (FFDI), it is shown that a strong relationship exists between climate variability, on a range of time scales, and forest fire risk. An investigation into the influence of ENSO on fire risk demonstrates that the proportion of days with a high, or greater than high, fire danger rating is markedly increased during El Nino episodes. More importantly, this study also shows that the already significantly enhanced fire danger associated with El Nino events was even further increased during El Nino events that occurred when the IPO was negative. The potential to use simple indices of climate variability to predict forest fire risk is therefore demonstrated to be significant.

Interdecadal Pacific variability and eastern Australian megadroughts over the last millennium

The Interdecadal Pacific Oscillation (IPO) influences multidecadal drought risk across the Pacific, but there are no millennial-length, high-resolution IPO reconstructions for quantifying long-term drought risk. In Australia, drought risk increases in positive phases of the IPO, yet few suitable rainfall proxies and short (∼100 years) instrumental records mean large uncertainties remain around drought frequency and duration. Likewise, it is unknown whether megadroughts have occurred in Australias past. In this study, an atmospheric teleconnection in the Indian Ocean midlatitudes linking East Antarctica and Australia is exploited to produce the first accurate, annually dated millennial-length IPO reconstruction from the Law Dome (East Antarctica) ice core. Combined with an eastern Australian rainfall proxy from Law Dome, the first millennial-length Australian megadrought (>5 year duration) reconstruction is presented. Eight megadroughts are identified including one 39 year drought (A.D. 1174–1212), which occurred during an unprecedented century of aridity (A.D. 1102–1212).

From barriers to limits to climate change adaptation: path dependency and the speed of change

Research on the barriers and limits to climate change adaptation identifies many factors, but describes few processes whereby adaptation is constrained or may indeed fail to avoid catastrophic losses. It often assumes that barriers are by and large distinct from limits to adaptation. We respond to recent calls for comparative studies that are able to further knowledge about the underlying drivers of barriers and limits to adaptation. We compare six cases from across Australia, including those in alpine areas, rivers, reefs, wetlands, small inland communities, and islands, with the aim of identifying common underlying drivers of barriers and limits to adaptation. We find that the path-dependent nature of the institutions that govern natural resources and public goods is a deep driver of barriers and limits to adaptation. Path-dependent institutions are resistant to change. When this resistance causes the changes necessary for adaptation to be slower than changes in climate, then it becomes a limit to adaptation.

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.

Natural hazards in Australia: droughts

Droughts are a recurrent and natural part of the Australian hydroclimate, with evidence of drought dating back thousands of years. However, our ability to monitor, attribute, forecast and manage drought is exposed as insufficient whenever a drought occurs. This paper summarises what is known about drought hazard, as opposed to the impacts of drought, in Australia and finds that, unlike other hydroclimatic hazards, we currently have very limited ability to tell when a drought will begin or end. Understanding, defining, monitoring, forecasting and managing drought is also complex due to the variety of temporal and spatial scales at which drought occurs and the diverse direct and indirect causes and consequences of drought. We argue that to improve understanding and management of drought, three key research challenges should be targeted: (1) defining and monitoring drought characteristics (i.e. frequency, start, duration, magnitude, and spatial extent) to remove confusion between drought causes, impacts and risks and better distinguish between drought, aridity, and water scarcity due to over-extractions; (2) documenting historical (instrumental and pre-instrumental) variation in drought to better understand baseline drought characteristics, enable more rigorous identification and attribution of drought events or trends, inform/evaluate hydrological and climate modelling activities and give insights into possible future drought scenarios; (3) improving the prediction and projection of drought characteristics with seasonal to multidecadal lead times and including more realistic modelling of the multiple factors that cause (or contribute to) drought so that the impacts of natural variability and anthropogenic climate change are accounted for and the reliability of long-term drought projections increases.

A New Approach to Stochastically Generating Six-Monthly Rainfall Sequences Based on Empirical Mode Decomposition

Abstract This paper introduces a new approach to stochastically generating rainfall sequences that can take into account natural climate phenomena, such as the El Nino–Southern Oscillation and the interdecadal Pacific oscillation. The approach is also amenable to modeling projected affects of anthropogenic climate change. The method uses a relatively new technique, empirical mode decomposition (EMD), to decompose a historical rainfall series into several independent time series that have different average periods and amplitudes. These time series are then recombined to form an intradecadal time series and an interdecadal time series. After separate stochastic generation of these two series, because they are independent, they can be recombined by summation to form a replicate equivalent to the historical data. The approach was applied to generate 6-monthly rainfall totals for six rainfall stations located near Canberra, Australia. The cross correlations were preserved by carrying out the stochastic analysi...