Introduction

Aldo Poiani

I Floods in an Arid Continent

On the morning of July 7, 1956, the town of Mildura in northwestern Victoria, Australia, a usually tranquil city overlooking the Murray River woke up to the news in the local newspaper, the Sunraysia Daily, that “Floodwaters are pushing hard against the network of levee banks around Wentworth and should they break through the town will be flooded.” Two days later, on July 9, the headlines announced that “Roads cut as floods spread in 3 states,” while “help of army sought to hold weakened levee bank.” The situation continued to worsen in the following days and the issue of July 11 warned on page 1 of a “Desperate fight to hold river. Thousands of people along the banks of the flood‐swollen Murray and its tributaries are fighting desperately to save their homes,” and on page 2, the people of Mildura began to realize the magnitude of the unfolding disaster as the “District faces worst flooding ever known—1931 peak neared.” Two days later, the eyes were on the levees as the flood level was expected to “near peak,” and on July 24 the paper grimly announced that “The main levee bank on the Murray at Mildura broke yesterday to make the present flood the most costly in the district's history.” On July 26, the Murray River was “at 1931 level—and still rising.” In fact, what the inhabitants of Mildura and Wentworth were experiencing firsthand was the unfolding of the worst flood to involve the Murray and Darling rivers in the twentieth century (Fig. 1).

Floods, generally defined as “a significant rise of water level in a stream, lake, reservoir or coastal region” (IRIN, 2005), have gained a dual identity of sorts. On the one hand, daily news abound in detailed accounts of natural disasters, with spectacular floods being a favorite subject of media attention. I am writing this chapter in mid‐April 2006 and a quick survey of the Australian Broadcasting Corporation, the American Broadcasting Corporation, CNN, and BBC Web sites for the first three and a half months of the year uncovers news about floods in Australia (Katherine River, Northern Territory; Murchison catchment, Western Australia; Bellinger River, New South Wales), Indonesia, India, United States (North Dakota, Minnesota), Malawi, and several countries in Europe (Czech Republic, Germany, Bulgaria, Greece, Poland, Hungary, Austria, Slovakia). Not surprisingly, floods are considered a major “natural disaster” that should be prevented or its effects on human populations mitigated if possible. On the other hand, floods can distribute nutrients throughout vast areas of floodplains and contribute to the maintenance of both natural and some agricultural ecosystems.

Floods have been impacting on biota, including human populations, since time immemorial. Plant and animal species inhabiting floodplains show adaptations presumably selected in response to recurrence of floods in the environment (Lytle and Poff, 2004). For instance, Eucalyptus camaldulensis is a typical flood tolerant tree species in Australia that has several physiological adaptations allowing trees to withstand the effects of flooding (Blake and Reid, 1981). From the particular perspective of our species, ancient civilizations developing along the basin of major river systems in all continents have been affected in one way or another by floods (Killick, 1985; Shendge, 1991; Hassan, 1998). Human experience with floods has given rise not only to flood myths and stories (e.g., see the Ridarngu song quoted above) but also to practical solutions to either exploit the benefits of floods or prevent the negative effects of floods through the establishment of flood mitigation procedures.

Australia is widely recognized as a mainly dry continent, with about 70% of the mainland being categorized as arid or semiarid (Stafford‐Smith and Morton, 1990). Yet, the risk of floods in the country is high in some regions. Although this book mainly focuses on the Murray–Darling Basin (MDB), a major system of rivers, wetlands, and floodplains covering a large extension of southeastern Australia, other areas at high flood risk, especially in the tropical north that is under a monsoonal regime, will be also considered in some of the chapters. Moreover, the MDB is also subject to the effects of climate in the tropics as floods in the Darling River are affected by the tropical climatic conditions that characterize the northern areas of the continent.

The book is organized into nine chapters, including this introductory chapter, that bring together experts in climatology, limnology, ornithology, landscape ecology, epidemiology, economics, anthropology, and sociology, addressing the causes and consequences of floods in Australia from the perspective of the physical environment, the biota, and human populations. In what follows, I will introduce the different chapters first to subsequently propose a preliminary synthesis of our knowledge of floods in Australia, with the aim of drawing some general conclusions that may be applicable to other regions as well.

Pittock et al. in their chapter review the Climatic background to past and future floods in Australia. They describe how the current climate in the northern parts of the Darling River catchment, especially in summer, is under the influence of troughs in the low‐latitude easterlies, that is, winds moving from east to west, and tropical atmospheric pressure lows that affect the extent of rainfall in the tropical rainy season; whereas rainfall in the southern regions of the MDB is affected by winter atmospheric pressure lows and also cold temperatures resulting from winds coming from the west (westerlies). These climatic conditions affecting the MDB determine the occurrence of summer floods on the Darling River and mostly winter floods along the Murray River. A major climatic influence on the probability of floods in the MDB is the El Niño‐Southern Oscillation (ENSO). In the opposite phase of ENSO, not surprisingly called “La Niña,” the northern and eastern parts of Australia tend to be subject to high rainfall that may cause floods. However, as indicated by Pittock et...