INTRODUCTION

The previous chapter was mainly concerned with the effects of strong winds generated by secondary features of general air circulation. These winds were associated with the development of low-pressure cells spanning areas of 10,000–100,000 km−2. While tropical cyclones and extra-tropical depressions produce some of the strongest winds and highest amounts of precipitation over the widest areas, they are by no means the only source of high winds or heavy precipitation. These values can be matched by thunderstorms, which cover no more than 500 km2 in area and rarely travel more than 100–200 km before dissipating. They can produce high-magnitude, short-period rainfalls leading to flash flooding. Thunderstorms are also associated with a wide range of climatic phenomena such as lightning, hail and tornadoes that bring death and destruction. Tornadoes generate the highest wind speeds and can produce localized wind damage just as severe as that produced by a tropical cyclone. This chapter will examine first the development and structure of thunderstorms resulting in lightning and hail. This is followed by a description of tornadoes and the major disasters associated with them. The chapter concludes with a discussion of warning and response to the tornado threat, an aspect that has been responsible for decreasing death tolls throughout the twentieth century.

THUNDERSTORMS, LIGHTNING AND HAIL

Thunderstorms

(Whipple, 1982; Eagleman, 1983)

Thunderstorms are a common feature of the Earth's environment. There are about 1800–2000 storms per hour or 44,000 per day.

INTRODUCTION

The earlier chapter on large-scale storms did not consider in detail the effects of flooding associated with tropical cyclones, extra-tropical storms or east-coast lows. Nor was it appropriate to discuss large-scale flooding in that chapter because some of the worst regional flooding in the northern hemisphere has occurred in spring in association with snowmelt. In addition, rainfall associated with thunderstorms is a major cause of flash flooding. This chapter examines flash flooding events and regional floods. Flash flooding refers to intense falls of rain in a relatively short period of time. Usually the spatial effect is localized. Modification of the overall landscape during a single event is minor in most vegetated landscapes; however, in arid, semi-arid, cultivated (where a high portion of the land is fallow) or urban areas, such events can be a major cause of erosion and damage. Steep drainage basins are also particularly prone to modification by flash floods because of their potential to generate the highest maximum probable rainfalls. Large-scale regional flooding represents the response of a major continental drainage basin to high-magnitude, low-frequency events. This regional flooding has been responsible historically for some of the largest death tolls attributable to any hazard. When river systems alter course as a response to flooding, then disruption to transport and agriculture can occur over a large area.

INTRODUCTION

The previous chapter concentrated upon large-scale pressure patterns and their changes across the surface of the Earth. While these patterns regionally control precipitation, large-scale vortices amplify the amounts and add a wind component to produce devastating storms. In addition, moderate-to-strong winds on a regional scale have the capacity to suspend large quantities of dust. This material can be transported thousands of kilometers, a process that represents a significant mechanism for the transport of sediment across the surface of the globe. Dust storms are exacerbated by drought in low rainfall, sparsely vegetated regions of the world. For that reason, they pose a slowly developing but significant hazard in sparsely settled semi-arid regions. Unfortunately, many of these areas have been marginalized by the degrading agricultural practices of humans over thousands of years. However, in some regions where settlement has occurred only in the last 200 years, we are presently witnessing this marginalization process. Dust storms are one of the most prominent and long-lasting signatures of human impact on the landscape.

In this chapter, the process, magnitude, and frequency of tropical cyclones are described first, followed by a description of some of the more familiar cyclone disasters. This section concludes with a comparison of the human response to cyclones in Australia, the United States, and Bangladesh – formerly East Pakistan.

INTRODUCTION

Drought and famine have plagued urban–agricultural societies since civilizations first developed. While many definitions exist, drought can be defined simply as an extended period of rainfall deficit during which agricultural biomass is severely curtailed. In some parts of the world, such as the north-east United States and southern England, a drought may have more of an effect on urban water supplies than on agriculture. The definition of drought, including the period of rainfall deficit prior to the event, varies worldwide. In southern Canada, for instance, a drought is any period where no rain has fallen in 30 days. Lack of rain for this length of time can severely reduce crop yields in an area where crops are sown, grown, and harvested in a period of three to four months. In Australia, such a definition is meaningless, as most of the country receives no rainfall for at least one 30-day period per year. Indeed, in tropical areas subject to monsoons, drought conditions occur each dry season: most of tropical Australia, even in coastal regions, endures a rainless dry season lasting several months. In Australia, drought is usually defined as a calendar year in which rainfall registers in the lower 10 per cent of all the records. Unfortunately, in the southern hemisphere, a calendar year splits the summer growing season in two. A more effective criterion for drought declaration should consider abnormally low rainfall in the summer growing season.

I have reread the preface to the first edition many times: extreme events, dire warnings about Green-house warming, El Niño–Southern Oscillation prediction … Little has changed in the fifteen years since I wrote about them. I am still perplexed because extreme events continue to happen and global warming is no closer to occurring. As Sydney in February 2004 experienced a heat wave of a magnitude unprecedented since at least 1939, I was chasing my favourite research topic – cosmogenically induced mega-tsunami – on Stewart Island, New Zealand some two thousand kilometres away where an unprecedented cold snap was occurring. One event witnessed by four million people got all the publicity; the other played out in a remote cabin in front of half of dozen trekkers got none. Yet both climatic extremes were produced by the same pattern of atmospheric circulation controlled by the same sequence of mobile polar highs. Sydney lay on the equatorial ‘greenhouse’ side of the highs and Stewart Island lay on the poleward ‘Ice Age’ side. This book covers two of the phenomena I experienced in my February of extremes – mobile polar highs and tsunami. As with the first edition, the book does not cover the third phenomena, Green-house warming. This book is about everyday climatic and geological hazards that can be explained, predicted, and alleviated.

RATIONALE

The field of environmental studies is usually introduced to students as one of two themes. The first examines human effects upon the Earth's environment, and is concerned ultimately with the question of whether or not people can irreversibly alter that environment. Such studies include the effect of human impact on climate, of land-use practices on the landscape in prehistoric and recent times, and of nuclear war upon the Earth's environment. The second theme totally disregards this question of human impact on the environment. It assumes that people are specks of dust moving through time subject to the whims of nature. In this sense, calamities are ‘acts of God’, events that make the headlines on the evening news, events you might wish on your worst enemy but would never want to witness yourself.

University and college courses dealing with this latter theme usually treat people as living within a hostile environment over which they have little control. Such courses go by the name of ‘“Natural” Hazards’. The difference between the two themes is aptly summarized by Sidle et al. (2003). Both themes describe hazards. The first theme can be categorized as chronic while the second is episodic or periodic. Chronic hazards would include desertification, soil degradation, and melting of permafrost. The causes could be due to humans or global warming. Periodic hazards are large magnitude events that appear over a short time period.

INTRODUCTION

In Chapter 3, waves were often mentioned as one of the main agents of erosion and destruction by storms. In fact, destructive waves can occur without storm events, and in association with other climatic and oceanographic factors such as heavy rainfall and high sea levels, to produce coastal erosion. In this sense, waves form part of a group of interlinked hazards associated with oceans. This chapter examines these and other oceanographic hazards. Wave mechanics and the process of wave generation will be outlined first followed by a description of wave height distribution worldwide. This section will conclude with an appraisal of the hazards posed by waves in the open ocean.

Wind is the prime mechanism for generating the destructive energy in waves. In cold oceans, seas or lakes, strong winds can produce another hazard – the beaching of drifting sea-ice. Sea-ice is generally advantageous along a coastline that experiences winter storms, because broken sea-ice can completely dampen the height of all but the highest waves. When frozen to the shoreline as shorefast ice, sea-ice can completely protect the shoreline from any storm erosion. However, floating ice is easily moved by winds of very low velocity. These winds might not generate appreciable waves, but they can drive sea-ice ashore and hundreds of metres inland. The force exerted by this ice can destroy almost all structures typically found adjacent to a shoreline.

Patterns of settlement

Archaeologists have always been interested in the way in which people used their environment, but the value of the systematic study of patterns of settlement only became apparent to them in the 1950s and early 1960s. Archaeological interest resulted from the work being done by geographers like Chorley and Haggett (1967), following in the footsteps of earlier scholars such as Christaller and Losch, who attempted to identify the regularities of spatial patterning which could be detected in many different parts of the world. These seemed, at least in part, to determine the position and reflect the size and status of each settlement. Obviously such theories had immediate and important applications in archaeology and were especially relevant to the attempts then in progress to recognise the earliest urban centres and to define the processes which led to their appearance. In order to achieve these aims and identify the early urban centres, archaeologists borrowed wholesale the geographers' concepts of the ranking of settlements, of central-place function and of ideal patterns of settlement forming hexagonal territories in an undifferentiated landscape.

The only way in which the archaeological evidence needed for these studies could be collected was by survey, and the 1950s and 1960s also saw a refinement of existing techniques and the development of new ones using first air photographs and then satellite imagery. These advances were coupled with an increasing sophistication in their application and interpretation.

The elaborate economic framework which we described in the last chapter was only possible because the Sumerians had developed what is probably the earliest recording system in the world. Even Egyptian hieroglyphics are thought to be slightly more recent. The earliest attempts at keeping records cannot be called a writing system, but seem to be an attempt to record simple transactions, and date back to the pre-pottery Neolithic period. Small clay tokens have been recovered in a limited number of shapes at several different sites from 00E7;atal Hüyük in Anatolia to Jarmo in Iraqi Kurdistan. These tokens, it is thought, were used to represent various commodities. In time, certain tokens seem to have come to represent certain types of goods, sheep or cattle for example (Fig. 10.1). Different sizes and shapes also came to represent different quantities, so that it was possible to keep a simple record of transactions by this means. Schmandt-Besserat has elaborated this initial idea to suggest how a more sophisticated genuine writing system may have developed from these simple beginnings (Schmandt-Besserat 1986). Her ideas are not universally accepted, but at the moment represent the most coherent attempt at explanation that we have.

The next stage in this development was a proliferation in the variety and complexity of tokens as more and more goods began to be exchanged, goods which included textiles and foodstuffs for instance.

Ever since the advent of Christianity, the lands of the Bible have exerted a special fascination for the people of western Europe and America.

After the last crusade, English contacts with these countries became somewhat tenuous. Although a few ships continued to ply between Europe and the Holy Land, reliable information about the region became very sparse and the stories increasingly apocryphal. The numerous editions of the travels of Sir John Mandeville remained a standard work for many years because there was nothing better on offer, even though the anonymous fourteenth-century author may never have left his own fireside having used other earlier works for his composition (Moseley 1983). It was only in the nineteenth century, when Britain established direct political relations with the Ottoman provinces as well as with Istanbul itself, that it again became possible for curious individuals to travel moderately freely in Syria, Palestine and Iraq. J. S. Buckingham, writing in 1827, claims to be the first European for a century to publish his travels in these countries, and he found it sensible to travel dressed as an Arab and to act as a Muslim. The dangers involved were many and real, coming from both men and beasts, as Austen Henry Layard found even fifty years later when he too adopted Muslim dress and customs for his journeys (Layard 1903).

We began by looking at the patterns made by settlements in the landscape. The largest of these settlements were the towns and cities. The city, ‘uru’ in Sumerian, was the focus of life on the Mesopotamian plain: it was seen as the ideological, commercial, administrative and social centre of the world around it, but we still know surprisingly little about the details of life in a third-millennium urban centre or about its physical appearance. This chapter will look at the earliest evidence we have for town planning and for some of the most prominent buildings within these important centres. (For a survey of the evidence see van de Mieroop 1997.)

This evidence is very incomplete: the cost of excavating an entire site has always been prohibitive, even in the comparatively wealthy days before the Second World War. An American expedition had to abandon the attempt in the 1930s to excavate the relatively small tell of Tepe Gawra in its entirety. About half-way down, the scale of the undertaking became apparent and funds began to run short. This means that, especially when dealing with large urban sites, such as Uruk, we are forced to deduce overall patterns from a number of small, disjointed scraps of evidence usually gained by survey and small-scale excavation, a thoroughly unsatisfactory situation. However, by using evidence from survey, from ethnography and from the texts, as well as from excavation, it is possible to make some general observations on the use of space in Sumerian towns and cities.

This book is intended for students, and especially for students beginning to study the archaeology and history of the ancient Near East. The changes which took place on the Mesopotamian plain between the Tigris and Euphrates rivers in the fourth and third millennia bc are of crucial importance in understanding subsequent developments in western Asia and beyond. A range of major innovations in both technology and social development is attributed to this period and it is these innovations which will be described in the following chapters. Many of them have their roots in much older periods. Where evidence which complements or extends that from Mesopotamia is available from adjacent geographic areas, it too will be included. Since 1991 it has not been possible to dig in Iraq itself and, as a direct result of this, there has been an explosion of archaeological activity in neighbouring countries such as Syria and the Gulf states. This new evidence has brought important new insights and has led to a reappraisal of the Sumerian world.

There are several ways of approaching such a study. One is the straightforward chronological account traditionally favoured by historians and archaeologists, which tries to describe a society in its entirety from genesis to extinction. More recently, authors have begun to isolate specific aspects of a society, taking one stimulus such as trade, or one theme such as the ecological background. The role of that specific factor in the development of the society is then explored.

As so many of the manufactured goods we have been discussing were made of imported materials, this seems an appropriate place to consider what is known of Mesopotamia's foreign trading contacts. It should be noted that the word ‘trade’ is being used very loosely in this discussion to cover the acquisition of foreign goods by any means, including foraging, pillaging and tribute. In addition, pedlars, craftsmen and, especially, women represent another channel by which goods were moved around over considerable distances. It is clear from the texts that diplomacy and trade were closely linked and that the daughters of the rulers of the city-states were often married to foreign royalty on the fringes of the Mesopotamian world as part of such diplomatic efforts. They took with them all the comforts of home, providing yet another method of exchanging goods, and no doubt this pattern was repeated at a less elevated social level with individual merchants consolidating their business ties by similar means. Foreign craftsmen working in Mesopotamia are sometimes referred to in the texts and may well have produced goods in foreign styles for the Mesopotamian market, thereby complicating the picture still further.

It is often almost impossible to distinguish archaeologically between these methods of acquiring goods and of moving them from one place to another and we will not attempt to do so here.