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Human activities also contribute to the development of drought conditions. Overgrazing, poor cropping methods and improper soil conservation techniques often contribute to creating the drought. (See Fig. 7.1.) Recurrence Interval Climatologists debate whether drought is a short-term aberration in the climate or the result of long-term climatic changes. Some argue that drought feeds upon itself; that as vegetation is stripped from the land, the surface dries out and reflects more of the sun’s heat. This would alter the thermal dynamics of the atmosphere and suppress rainfall, which would, in turn, dry out more land. This process is discussed in the chapter on desertification. Historically, droughts have tended to occur at regular intervals. Many scientists have noted that in areas where long-term droughts have been prevalent, surges of dry periods apparently occur at relatively predictable intervals. With this in mind, climatologists are seeking to compile historical records of drought so that drought forecasting can be made more accurate. Whether precisely predictable or not, the historical trends can give an indication as to when drought periods might be expected. For this reason, it is important that persons living in marginal or semiarid areas try to learn about the history of drought in a particular region and use this knowledge as a rule of thumb in predicting future drought periods. 5 Impact of Droughts on Built and Natural Environments The effects of droughts can be divided according to the primary or immediate effects, and the secondary or resulting effects. Primary Effects Primary effects of drought result from a lack of water. As a dry period progresses and water supplies dwindle, existing water supplies are overtaxed and finally dry up. The primary losses are loss of crops, loss of livestock and other animals, and loss of water for hygienic use and drinking. Secondary Effects of Drought The secondary effects of drought follow and result from the primary effects. As water supplies dwindle and crops and fodder are depleted, families begin to migrate in search of better grazing lands for their herds or move to the cities to seek jobs and alternative sources of income. If the dwindling supplies of food are not replaced, famine can occur, further accelerating the migration out of the stricken areas to less affected zones. The migration may, in itself, contribute to spreading the scope of the disaster, especially if grazing animals are moved with the people. If drought is long term, it may result in permanent changes of settlement, social, and living patterns. For example, before the 1968 drought, 65 percent of Mauritania’s population were nomads. By 1976 that figure was down to 36 percent. The town of Nouakchott grew from 12,300 in 1964 to approximately 135,000 20 years later. Secondary effects of droughts also include major ecological changes, such as increased scrub growth, increased flash flooding and increased wind erosion of soils. Of these, desertification is the most concern.
The Drought Cycle Normal Hydrological Balance: Water supply is adequate to meet demand. The community grows and land use intensifies. Drought: Meteorological changes reduce rainfall, while urbanization, overgrazing, reforestation, and farming reduce water retention of the soil. The normal hydrological balance is broken. The topsoil erodes and the water table is lowered making recovery difficult. Food production and drinking water are reduced and people migrate out of the area. Figure 7.1
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Natural Hazards: Causes and Effects
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This publication was prepared by th
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Introduction How to Get Started Thi
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eruption may be the saturation of a
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Course Objectives Lesson 1 Introduc
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Lesson 1 - Introduction to Natural
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_____ 9. The transitional period an
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Lesson 2 - Self-Assessment Test Mul
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Lesson 3 - Tsunamis Study Guide Ove
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Lesson 4 - Volcanoes Study Guide Ov
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a) frequency of tremors b) upward m
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) two secondary responses handled b
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Lesson 7 - Drought Study Guide Over
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) often easier than implementing th
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Lesson 9 - Deforestation Study Guid
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10. One method holding great promis
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Natural Hazards: Causes and Effects
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Contents List of Figures List of Ta
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Chapter 1 Introduction to Natural H
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Type of Event Number of People Kill
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Low-income Economy Afghanistan Bang
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Phases of a Disaster Disaster speci
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Effects of Disasters Each type of d
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take steps to prevent the disaster,
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Chapter 2 Earthquakes Introduction
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Himalayan zone. Most earthquakes ap
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The different rates of travel betwe
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Modified Mercalli Intensity Scale o
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Frequency of Earthquakes More than
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How an earthquake damages a house F
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Rupture Zones and Epicenters in Cen
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of population from rural to urban a
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In all emergency activities it is o
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Notes 1 Rita Funaro-Curtis, Natural
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foundations by the water buoyancy.
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Impact on Natural and Built Environ
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Disaster Mitigation The most system
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- for tsunamis of local origin, pot
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Chapter 4 Volcanoes Introduction Ov
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production of sugar and cattle. Bec
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lava is a thin fluid (not viscous),
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then cool as thin, gently dipping s
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drains, causing flooding during sub
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then recognized, but today an incre
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Volcanic Zoning and Risk Mapping Wi
Page 97 and 98: 1. Environmental Effects Volcano Di
Page 99 and 100: Altogether the combined disaster of
Page 101 and 102: force caused by the earth’s rotat
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Page 105 and 106: The Saffir / Simpson Hurricane Scal
Page 107 and 108: measures as have to be devised and
Page 109 and 110: Storm Surge Source: Cuny, Disasters
Page 111 and 112: a set of activities in anticipation
Page 113 and 114: and buildings will affect the veloc
Page 115 and 116: How High Winds Damage Buildings Win
Page 117 and 118: • developing an effective forecas
Page 119 and 120: Notes 1 INTERTECT, The Potential Co
Page 121 and 122: 1. Environmental Effects Tropical C
Page 123 and 124: also by human changes to the surfac
Page 125 and 126: The most noted floods are associate
Page 127 and 128: Magmatic Water ATMOSPHERE The Hydro
Page 129 and 130: Seasonality —Inundation of land d
Page 131 and 132: • Since Landsat images are taken
Page 133 and 134: The second step in vulnerability re
Page 135 and 136: 100-year flood, since this frequenc
Page 137 and 138: • Publish a master plan report wi
Page 139 and 140: • Blankets can be useful, but if
Page 141 and 142: Initial Response By Local Authoriti
Page 143 and 144: Notes 1 INTERTECT, The Potential Co
Page 145 and 146: Chapter 7 Drought Introduction Drou
Page 147: In addition to the droughts in the
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Page 153 and 154: land aware of the issues. Planning
Page 155 and 156: The importance of responding to the
Page 157 and 158: Chapter 8 Desertification Introduct
Page 159 and 160: Region Estimates of Populations and
Page 161 and 162: 1960; 500,000 in 1973. In 1975, in
Page 163 and 164: Adaptation of the Hydrological Cycl
Page 165 and 166: eluctance to cut back on stock numb
Page 167 and 168: effect. Finer materials are lifted
Page 169 and 170: such measures involve the disruptio
Page 171 and 172: Slash-and-Burn Agriculture. This me
Page 173 and 174: Issues in Reconstruction Peculiar t
Page 175 and 176: Chapter 9 Deforestation Introductio
Page 177 and 178: uncontrolled deforestation is a sym
Page 179 and 180: Related Disasters Description of Ph
Page 181 and 182: exploitable timber available per pe
Page 183 and 184: implementation. But essential as th
Page 185 and 186: Analogue modeling — the applicati
Page 187 and 188: Crater — a bowl-shaped depression
Page 189 and 190: organizations (public and private),
Page 191 and 192: Fault — a planar or gently curved
Page 193 and 194: Hurricane — in the Western Hemisp
Page 195 and 196: Malnutrition — the condition of s
Page 197 and 198: Precipitation — in meteorology, w
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— S — Sand dune stabilization
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Telemetry — the use of communicat
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Vulnerability — the extent to whi
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International Society on Disaster M
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University of Colorado Natural Haza
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Disaster Management Center Universi
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