Deserts and Desert Environments

Taking a global perspective, this book provides a concise overview of drylands, including their physical, biological, temporal, and human components.

• Examines the physical systems occurring in desert environments, including climate, hydrology, past and present lakes, weathering, hillslopes, geomorphic surfaces, water as a geomorphic agent, and aeolian processes
• Offers an accessible introduction to the physical, biological, temporal, and human components of drylands
• Investigates the nature, environmental requirements, and essential geomorphic roles of plants and animals in this stressful biological environment
• Highlights the impact of human population growth on climate, desertification, water resources, and dust storm activity
• Includes an examination of surface/atmosphere interactions and the impact of ENSO events.

Preface xii

1 Introduction: defining the desert system 1

1.1 Defining the desert system 1

1.2 Evolution of deserts 2

1.3 Indices of aridity 6

1.4 Desert surfaces 8

1.5 Tectonically stable and unstable deserts 8

1.6 Deserts of the past 9

1.7 Changing human perspectives on deserts 12

2 Deserts of the world 14

2.1 Introduction: the extent of global aridity 14

2.2 Global deserts 14

3 The climatic framework 48

3.1 Introduction: classification of deserts by temperature 48

3.2 Weather data 48

3.3 Atmospheric controls: surface boundary layer 50

3.4 Temporal and spatial variability of climatic influences 64

4 The hydrologic framework 71

4.1 Introduction 71

4.2 The water balance in deserts 71

4.3 Water budgets 73

4.4 Surface runoff and floods 84

4.5 The chemical quality of surface and soil water 89

4.6 Water resources 90

4.7 Case study: the waters of the Tigris-Euphrates Basin and the impact of modern water management 94

5 Lake systems: past and present 98

5.1 Introduction to desert lakes 98

5.2 Types of lake 98

5.3 Lakes of the global arid environment 106

6 Weathering processes and hillslope systems 122

6.1 Introduction 122

6.2 Weathering 122

6.3 Weathering forms 126

6.4 Duricrusts 128

6.5 Desert varnish 134

6.6 Hillslope processes 136

6.7. Composite surfaces (pediments) 145

7 Desert soils and geomorphic surfaces 148

7.1 Introduction 148

7.2 The nature of soils in arid and semiarid regions 148

7.3 Soil description and classification 149

7.4 Soil characteristics of arid regions 150

7.5 Inorganic and biological soil crusts 152

7.6 Spatial heterogeneity in soil properties and the ecohydrology of patterned vegetation zones 156

7.7 Surface volume changes 158

7.8 Surface types: hamada and stone pavements 159

8 Water as a geomorphic agent 168

8.1 Introduction 168

8.2 Groundwater sapping in slope and valley development 168

8.3 Piping processes in channel and slope evolution 171

8.4 Fluvial processes 172

8.5 Fluvial landforms 179

9 Aeolian processes 186

9.1 Introduction 186

9.2 Near-surface flow 187

9.3 Wind processes 191

9.4 Landforms of accumulation: sand sheets, zibar, and sand stringers 195

9.5 Landforms of accumulation: dunes 197

9.6 Ripples 213

10 Landforms of aeolian erosion and desert dust 216

10.1 Introduction 216

10.2 Deflation features: desert depressions and pans 216

10.3 Ventifacts 218

10.4 Yardangs and ridge and swale systems 221

10.5 Desert dust 225

11 Plant communities and their geomorphic impacts 237

11.1 Introduction: characteristics of desert ecosystems 237

11.2 Adaptations to desert conditions 238

11.3 Plant communities and ecotones 245

11.4 Succession in desert plant communities 251

11.5 Dune communities 252

11.6 Vegetation type and density and relationship to geomorphic processes 253

12 Animal communities 259

12.1 Introduction: environmental requirements 259

12.2 Effects on geomorphic processes 264

12.3 Hydrologic impacts 265

12.4 Effects of the geomorphic activity of animals on plant communities 266

13 Desertification and the human dimension 267

13.1 Desertification: introduction and terminology 267

13.2 Climate change and desertification 268

13.3 Anthropogenic causes of desertification 269

13.4 Water resources: a rural and urban problem 275

13.5 Case study: the Aral Sea 280

13.6 Discussion 283

References 285

Index 320

"All chapters of the book are preceded by a short introduction, which is very useful. The book is
richly illustrated in the form of both black-and-white and colour photos (but the colour figures
duplicate the black-and-white ones!), graphs and diagrams . . . taken all together, the book can be recommended to graduate students and researchers dealing with deserts; sedimentology is certainly not the main topic, but much information is very useful to increase the insight into the conditions that control the sedimentological processes in this environment." (Society for Sedimentary Research, 2011)

"I would recommend Deserts and Desert Environments as a useful starting point for any undergraduate student wishing to explore a range of dryland environments and landforms for the first time. The well-illustrated and accessible nature of this text-book will suit them well". (The Geographical Journal, 1 March 2010)

"Each chapter of the book is preceded by a short introduction, which is very useful. The book is richly illustrated in the form of both black-and-white and colour photos (but the colour photos duplicate the black-and-white ones!), graphs and diagrams." (Geologos, July 2010)

Julie Laity is a Professor at California State University, Northridge, USA. Her work has focused on deserts, looking at aeolian, fluvial, and groundwater systems, and the impact of environmental degradation on wind-blown sand and dust events. Her research on groundwater-sapping systems and wind erosion has been used to aid our understanding of Martian environments.

Deserts and Desert Environments focuses on geomorphic systems, providing a comprehensive introduction to the physical, biological, temporal, and human components of drylands. Taking a global perspective, the book:

• examines physical systems, including climate, hydrology, past and present lakes, weathering, hillslopes, geomorphic surfaces, water as a geomorphic agent, and aeolian processes
• investigates the nature, environmental requirements, and essential geomorphic roles of plants and animals in this stressful biological environment
• considers the impact of human population growth on climate, desertification, water resources, and dust-storm activity
• covers surface/atmosphere interactions and the impact of El Niño Southern Oscillation events, exploring recent advances in understanding the temporal and spatial variability of deserts.

The breadth of coverage and accessible style make Deserts and Desert Environments ideal for introductory students of desert systems or desert geomorphology, as well as a useful reference for scientists and environmental professionals.