Major coastal flooding in southeastern Australia, associated deaths and weather systems

Abstract

A new historical database describing major floods and associated weather systems that occurred in coastal catchments, from Brisbane in southeastern Australia to Eden approximately 1500 km further south, is described. In order to produce a homogeneous record of major flood and weather-type frequency we restrict attention to the period 1860-2012, when the region (i) is extensively populated, (ii) has an extensive coverage of meteorological stations, (iii) is extensively connected by telecommunication, and (iv) when there is busy coastal shipping offshore. A total of 253 major floods over this period are identified. A flood is considered here to be 'major' if it causes inundation of a river within approximately 50 km of the coast or if there is non-riverine flooding over land near the coast, extending 20 km or more along the coast. All major floods are associated with either (a) East Coast Lows (ECLs) or (b) Tropical Interactions (TIs). Three types of TIs are identified and described. ECLs triggered more major floods than TIs (57 per cent versus 43 per cent), but TIs caused more deaths from freshwater flooding (62 per cent versus 38 per cent) and they tended to cause over twice as many deaths per event (3.6 versus 1.7 deaths/event on average). Some of the most extreme events identified occurred in the 19th century and early-to-mid 20th century. If such events were to occur today they would have catastrophic impacts due to the massive increase in urban development in the study region since that time. IntroductionMajor floods frequently isolate towns, and can cause death, major disruptions to road and rail links, the evacuation of many houses and business premises, and the widespread flooding of farmland. Major flooding can lead to high death tolls. For example, there were at least 90 known deaths caused by floods in June 1852, and 25 deaths during the Brisbane River catchment floods in January 2011.Given these severe impacts, it is of interest to know how frequently major floods have occurred in the past and what weather systems were associated with such floods. We therefore examine a large number of historical records describing floods, and associated weather and impacts. We restrict attention to major floods that have occurred in coastal catchments in eastern Australia during 1860-2012 in the north to Eden (New South Wales (NSW)) 1500 km further south. The study region is depicted in Fig. 1. Over six million people live in this rapidly developing zone.As we are specifically concerned with major flooding near the coast, we consider a flood to be major if (i) it causes inundation of a river within approximately 50 km of the coast or (ii) if there is non-riverine flooding overland near the coast, from the active part of a weather system, that extends at least 20 km along the coast. In (i) extreme rainfall extends well into the hinterland and the upper reaches of the river catchments, causing a flood that drains down the river systems to coastal areas. In (ii) extreme rainfall is confined to the coast and floods form ...

Current climate data rescue activities in Australia

“…The data recovered are already informing historical studies (Gergis et al, 2010), global reanalysis products (Allan et al, 2011;Cram et al, 2015) and long-term climate variability assessments (Callaghan and Power, 2014). There are still many more sources of historical climate data for Australia to be uncovered and a new regional data rescue focus of the International Atmospheric Circulation Reconstructions over the Earth Initiative (ACRE, Allan et al 2011) -ACRE Australia -is planned.…”

Identifying East Coast Lows with climate hazards on the eastern seaboard

“…The manually-developed databases of Callaghan and Helman (2008), Speer et al (2009) and Callaghan and Power (2014) incorporate human pattern recognition skills as well as knowledge of associated impacts, and thus contain the majority of severe or intense events. However, such databases are time-consuming to produce and require further manual work to update over time.…”

“…Further information on East Coast Lows with erosion or shipping impacts is available in Callaghan and Helman (2008), and ECLs associated with severe flooding in Callaghan and Power (2014). Due to limits of availability of both wind and wave data prior to the mid-1970s, this data is restricted to the period from 1970.…”

The frequency of major flooding in coastal southeast Australia has significantly increased since the late 19th century

“…Concerns are further fuelled by an increased coverage of flooding in the media (Kundezewicz et al 2012). Unfortunately, there is low confidence in the scientific community regarding even the sign of observed changes in flood frequency in many places, as flood records in many parts of the world are often sparse in space, and short or interrupted in time (Callaghan and Power 2014, Bates et al 2008, Seneviratne et al 2012, Kundzewicz et al 2014. It is therefore important that flood records around the world be improved and extended back as far as possible using instrumental and other historical records (Kundzewicz et al 2014).…”

“…Given the vulnerability of the region to flooding and the need to improve the documentation of flood trends, it is fortunate and timely that Callaghan and Power (2014) recently described a new uninterrupted record of major flood frequency for a continuous 1500 km stretch of coastal catchments in southeast Australia. The population in this region is growing rapidly and this growth is driving very strong urban development.…”