Series Foreword xiv
Preface xv
Acknowledgements xvii
About the Companion Website xviii
1 The Hydrological Cycle 1
1.1 Overview 1
1.2 Processes comprising the hydrological cycle 3
1.3 Global influences on the hydrological cycle 4
1.4 Water balance 6
1.5 Impact of aerosols on the hydrological cycle 6
1.6 Coupled models for the hydrological cycle 7
1.7 Global Energy and Water Cycle Exchanges Project (GEWEX) 8
1.8 Flooding 8
Summary of key points in this chapter 9
Problems 10
References 10
2 Precipitation 11
2.1 Introduction 11
2.2 Equation of state for a perfect gas 11
2.3 Hydrostatic pressure law 12
2.4 First law of thermodynamics 12
2.5 Atmospheric processes: dry adiabatic lapse rate 13
2.6 Water vapour in the atmosphere 15
2.7 Atmospheric processes: saturated adiabatic lapse rate 16
2.8 Stability and convection in the atmosphere 16
2.9 The growth of precipitation particles 18
2.10 Precipitation systems 21
2.10.1 Localized convection 22
2.10.2 Mesoscale precipitation systems 23
2.10.3 Mid¢latitude depressions 26
2.10.4 Tropical storms 30
2.10.5 Orographic effects on precipitation distribution 31
2.10.6 Topographical effects on precipitation distribution 33
2.11 Global atmospheric circulation 33
Appendix 2.1 Growth of a raindrop 33
Summary of key points in this chapter 35
Problems 36
References 37
3 Evaporation and Transpiration 41
3.1 Introduction 41
3.2 Modelling potential evaporation based upon observations 41
3.3 Aerodynamic approach 42
3.4 Energy balance 44
3.5 The Penman equation 44
3.6 Sensible and water vapour fluxes 45
3.7 Evaporation of water from wet vegetation surfaces: the interception process 47
3.8 Measuring evaporation and transpiration 47
3.9 Water circulation in the soil¢"plant¢"atmosphere continuum 48
3.10 Water circulation and transpiration 50
3.11 Water flux in plants 50
3.12 Modelling land surface temperatures and fluxes 51
3.13 Soil¢"vegetation¢"atmosphere transfer schemes 54
3.14 Estimation of large scale evapotranspiration and total water storage in a river basin 56
Appendix 3.1 Combination of aerodynamic and energy balance methods of computing lake evaporation 57
Appendix 3.2 Modelling soil moisture wetness 57
Summary of key points in this chapter 58
Problems 59
References 60
4 Snow and Ice 63
4.1 Introduction 63
4.2 Basic processes 63
4.2.1 Formation of snow 63
4.2.2 Formation of snow cover and its effects on the atmosphere 65
4.2.3 Formation of ice 67
4.3 Characteristics of snow cover 68
4.4 Glaciers 70
4.5 Sea ice 71
4.6 Permafrost 71
4.7 The physics of melting and water movement through snow 71
4.8 Water equivalent of snow 74
4.9 Modelling snowmelt and stream flow 76
4.10 Snow avalanches 80
4.11 Worldwide distribution and extremes of snow cover 81
Appendix 4.1 Estimates of catchment snowmelt inflow rates 83
Summary of key points in this chapter 84
Problems 86
References 87
5 Measurements and Instrumentation 90
5.1 Measurement, resolution, precision and accuracy 90
5.2 Point measurements of precipitation 90
5.2.1 Raingauge types 90
5.2.2 Measuring snow and hail 92
5.2.3 Errors in measurement 94
5.3 Areal measurements of precipitation using raingauge networks 96
5.4 Radar measurements of rainfall 96
5.4.1 Basics 96
5.4.2 Errors in radar measurements 97
5.4.3 Adjustment using raingauges 101
5.4.4 Summary of problem areas associated with radar measurements of precipitation 102
5.4.5 The use of multi¢parameter radar 103
5.4.6 Drop size distributions 104
5.4.7 Rainfall estimation using parametric variables 104
5.4.8 Measurement of snow 106
5.4.9 Measurement of hail 107
5.4.10 Precipitation type 108
5.5 Soil moisture 109
5.5.1 Approaches 109
5.5.2 Gravimetric method 109
5.5.3 Electrical resistance method 110
5.5.4 Neutron method 110
5.5.5 Gamma ray attenuation method 110
5.5.6 Cosmos¢UK 111
5.5.7 Dielectric methods 111
5.5.8 Tensiometric method 113
5.5.9 Satellite remote sensing 113
5.6 Evaporation and evapotranspiration 113
5.7 Flow measurement: basic hydrometry 113
5.8 Measuring stream discharge 115
5.8.1 The stage¢discharge curve 115
5.8.2 Automated moving boat methods 117
5.9 Brief overview of modern telemetry 117
5.9.1 Ground¢based telemetry links 117
5.9.2 VHF and UHF radio links 117
5.9.3 Satellite links 118
Appendix 5.1 Combining dissimilar estimates by the method of least squares 118
Summary of key points in this chapter 119
Problems 121
References 121
6 Satellite¢Based Remote Sensing 125
6.1 Overview of satellite remote sensing 125
6.2 Surface scattering of electromagnetic radiation 129
6.3 Interaction of electromagnetic radiation with the atmosphere 131
6.4 Visible and infrared data 132
6.4.1 Precipitation 134
6.4.2 Snow depth 135
6.4.3 Soil moisture and evapotranspiration 136
6.5 Multispectral data 137
6.5.1 Precipitation 137
6.5.2 Cloud recognition 137
6.5.3 Snow 138
6.6 Passive microwave techniques 138
6.6.1 Precipitation 141
6.6.2 Global Precipitation Climatology Project (GPCP) 143
6.6.3 Global Precipitation Measurement mission (GPM) 143
6.6.4 Snow depth 143
6.6.5 Sea ice and sea surface temperature 145
6.6.6 Soil moisture and evapotranspiration 145
6.7 Active (radar) microwave techniques 147
6.7.1 Synthetic aperture radar 147
6.7.2 Radar systems 149
6.7.3 Tropical Rainfall Measuring Mission (TRMM) 150
6.8 The surface energy balance system (SEBS) 150
6.9 Summary of satellite measurement issues 151
Appendix 6.1 Radiation balance 154
Summary of key points in this chapter 155
Problems 157
References 157
7 Analysis of Precipitation Fields and Flood Frequency 163
7.1 Introduction 163
7.2 Areal mean precipitation 163
7.3 Spatial and temporal storm analysis 165
7.3.1 Spatial statistical analyses 165
7.3.2 Temporal analyses 167
7.3.3 Oscillations in precipitation 168
7.3.4 Conditional probabilities 169
7.3.5 Kriging 169
7.3.6 Accuracy of the precipitation products 171
7.4 Model storms for design 172
7.5 Approaches to estimating flood frequency 173
7.6 Probable maximum precipitation (PMP) 175
7.7 Probable maximum flood (PMF) 177
7.8 Flood Studies Report (FSR) 177
7.9 Flood Estimation Handbook (FEH) 180
Appendix 7.1 Three-dimensional description of a rainfall surface 182
Appendix 7.2 Gumbel distribution 183
Summary of key points in this chapter 183
Problems 185
References 185
8 Precipitation Forecasting 188
8.1 Introduction 188
8.2 Nowcasting 188
8.2.1 Definition 188
8.2.2 Impact of errors in precipitation measurements 189
8.2.3 Extrapolation of radar data 189
8.3 Probabilistic radar nowcasting 192
8.4 Numerical models: structure, data requirements, data assimilation 194
8.4.1 Probabilistic quantitative precipitation forecasting 194
8.4.2 Mesoscale models 197
8.4.3 Data assimilation 197
8.4.4 Performance of high resolution mesoscale model¢based nowcasting systems 198
8.5 Medium range forecasting 198
8.6 Seasonal forecasting 201
Appendix 8.1 Brier skill score 203
Summary of key points in this chapter 203
Problems 205
References 205
9 Flow Forecasting 209
9.1 Basic flood forecasting techniques 209
9.2 Model calibration and equifinality 210
9.3 Flood forecasting model development 210
9.4 Conversion of detailed hydrodynamic models to simplified models suitable for real¢time flood forecasting 213
9.5 Probabilistic flood forecasting and decision support methods 215
9.6 Derivation of station rating (stage¢discharge) curves 216
9.7 Performance testing of forecasting models and updating procedures 216
9.8 Configuration of models on to national and international forecasting platforms 218
9.9 Flood warnings and levels of service 222
9.9.1 United Kingdom 222
9.9.2 United States and Canada 222
9.10 Case studies worldwide: river and urban 224
Appendix 9.1 St Venant equations 224
Appendix 9.2 Flow in unsaturated and saturated zones 226
Summary of key points in this chapter 227
Problems 228
References 229
10 Coastal Flood Forecasting 233
10.1 Types of coastal flooding 233
10.2 Models used to predict storm surge flooding 233
10.2.1 Empirical models 234
10.2.2 First¢generation models 235
10.2.3 Second¢generation models 235
10.2.4 Third¢generation models 235
10.2.5 Wave, tide and surge models 235
10.3 Probabilistic surge forecasting 238
10.4 Tsunamis 239
10.5 Examples of coastal flooding in the United Kingdom 241
10.5.1 The surge of 1953 241
10.5.2 Wirral floods 2013 241
10.5.3 Surges along the east coast of England, December 2013 241
10.5.4 Aberystwyth floods January 2014 242
10.6 Some examples of coastal flooding worldwide 243
Appendix 10.1 Wave overtopping at the coast 244
Summary of key points in this chapter 245
Problems 247
References 247
11 Drought 249
11.1 Definitions 249
11.2 Drought indices 250
11.3 The physics of drought 253
11.4 Frequency analysis: predictability 254
11.5 Modelling the occurrence of drought 256
11.6 Major drought worldwide 258
11.7 Examples of the consequences of drought 258
11.8 Strategies for drought protection, mitigation or relief 260
Appendix 11.1 Defining aridity 261
Summary of key points in this chapter 261
Problems 263
References 263
12 Wind and the Global Circulation 266
12.1 Equations of motion 266
12.2 Atmospheric Ekman layer 268
12.3 Fronts 269
12.4 Jet streams 270
12.5 Hurricanes 271
12.6 Lee waves 272
12.7 Land and sea breezes 272
12.8 The wind structure of the atmospheric circulation 273
12.9 Hadley cell 273
12.10 Polar cell 274
12.11 Ferrel cell 275
12.12 Walker circulation 275
12.13 El Ni±o/Southern Oscillation 276
12.14 Monsoons 276
Appendix 12.1 Large scale air motion 278
Appendix 12.2 Ageostrophic motion 278
Summary of key points in this chapter 279
Problems 281
References 282
13 Climatic Variations and the Hydrological Cycle 284
13.1 An introduction to climate 284
13.2 Evidence of climate change 286
13.2.1 Climatology of the last ice age 292
13.2.2 Intergovernmental Panel on Climate Change (IPCC) 295
13.3 Causes of climatic change 297
13.3.1 The natural energy system 298
13.3.2 The hydrological cycle 299
13.3.3 The carbon cycle 301
13.3.4 Other biochemical cycles 301
13.4 Modelling climatic change 303
13.5 Possible effects of climate change upon the hydrological cycle and water resources 307
Appendix 13.1 Estimating return times for events in a long term climate record 310
Summary of key points in this chapter 310
Problems 313
References 314
14 Hydrometeorology in the Urban Environment 318
14.1 Introduction 318
14.2 Urban boundary layer and the water cycle 318
14.3 Urban development and rainfall 320
14.4 Sewer flooding 322
14.5 Surface runoff from urban areas 324
14.6 Floodplain development 326
14.7 Acid rain 327
14.7.1 Basics 327
14.7.2 Modelling wet deposition 328
14.8 Urban air and water pollution 329
Appendix 14.1 Number of runoff events from an urban drainage system 330
Summary of key points in this chapter 331
Problems 332
References 333
Glossary 336
Index 347
