Terrestrial Hydrometeorology

Dr. Shuttleworth worked for 20 years at the UK’s Institute of Hydrology, ultimately as Head of the Hydrological Processes Division. In 1993 he joined the University of Arizona where he is Regents’ Professor in both the Department of Hydrology and Water Resources and the Atmospheric Sciences Department. He has served on numerous national and international scientific advisory committees, including the National Research Council, the International Council of Scientific Unions, the International Hydrology Programme, the International Geosphere-Biosphere Programme, and the World Climate Research Programme. In 2001 Dr. Shuttleworth was awarded the AGU Hydrology Prize for “outstanding contributions to the science of hydrology”, and in 2006 IAHS, UNESCO and WMO jointly awarded him the prestigious International Hydrology Prize.

Foreword xvi

Preface xviii

Acknowledgements xix

1 Terrestrial Hydrometeorology and the Global Water Cycle 1

Introduction 1

Water in the Earth system 2

Components of the global hydroclimate system 4

Atmosphere 5

Hydrosphere 8

Cryosphere 9

Lithosphere 9

Biosphere 10

Anthroposphere 10

Important points in this chapter 12

2 Water Vapor in the Atmosphere 14

Introduction 14

Latent heat 14

Atmospheric water vapor content 15

Ideal Gas Law 16

Virtual temperature 17

Saturated vapor pressure 18

Measures of saturation 20

Measuring the vapor pressure of air 21

Important points in this chapter 23

3 Vertical Gradients in the Atmosphere 25

Introduction 25

Hydrostatic pressure law 26

Adiabatic lapse rates 27

Dry adiabatic lapse rate 27

Moist adiabatic lapse rate 28

Environmental lapse rate 28

Vertical pressure and temperature gradients 29

Potential temperature 30

Virtual potential temperature 31

Atmospheric stability 32

Static stability parameter 32

Important points in this chapter 34

4 Surface Energy Fluxes 36

Introduction 36

Latent and sensible heat fluxes 37

Energy balance of an ideal surface 38

Net radiation, Rn 38

Latent heat flux, λE 39

Sensible heat flux, H 39

Soil heat flux, G 39

Physical energy storage, St 40

Biochemical energy storage, P 40

Advected energy, Ad 41

Flux sign convention 41

Evaporative fraction and Bowen ratio 45

Energy budget of open water 46

Important points in this chapter 46

5 Terrestrial Radiation 48

Introduction 48

Blackbody radiation laws 49

Radiation exchange for ‘gray’ surfaces 51

Integrated radiation parameters for natural surfaces 52

Maximum solar radiation at the top of atmosphere 54

Maximum solar radiation at the ground 56

Atmospheric attenuation of solar radiation 58

Actual solar radiation at the ground 59

Longwave radiation 59

Net radiation at the surface 62

Height dependence of net radiation 63

Important points in this chapter 64

6 Soil Temperature and Heat Flux 66

Introduction 66

Soil surface temperature 66

Subsurface soil temperatures 67

Thermal properties of soil 68

Density of soil, ρs 69

Specific heat of soil, cs 70

Heat capacity per unit volume, Cs 70

Thermal conductivity, ks 70

Thermal diffusivity, αs 71

Formal description of soil heat flow 71

Thermal waves in homogeneous soil 72

Important points in this chapter 75

7 Measuring Surface Heat Fluxes 77

Introduction 77

Measuring solar radiation 77

Daily estimates of cloud cover 77

Thermoelectric pyranometers 78

Photoelectric pyranometers 79

Measuring net radiation 80

Measuring soil heat flux 81

Measuring latent and sensible heat 82

Micrometeorological measurement of surface energy fluxes 83

Bowen ratio/energy budget method 83

Eddy correlation method 85

Evaporation measurement from integrated water loss 87

Evaporation pans 88

Watersheds and lakes 89

Lysimeters 90

Soil moisture depletion 91

Comparison of evaporation measuring methods 91

Important points in this chapter 94

8 General Circulation Models 96

Introduction 96

What are General Circulation Models? 96

How are General Circulation Models used? 98

How do General Circulation Models work? 100

Sequence of operations 100

Solving the dynamics 102

Calculating the physics 103

Intergovernmental Panel on Climate Change (IPCC) 104

Important points in this chapter 105

9 Global Scale Influences on Hydrometeorology 107

Introduction 107

Global scale influences on atmospheric circulation 107

Planetary interrelationship 109

Latitudinal differences in solar energy input 109

Seasonal perturbations 109

Daily perturbations 109

Persistent perturbations 109

Contrast in ocean to continent surface exchanges 109

Continental topography 109

Temporary perturbations 110

Perturbations in oceanic circulation 110

Perturbations in atmospheric content 110

Perturbations in continental land cover 110

Latitudinal imbalance in radiant energy 110

Lower atmosphere circulation 111

Latitudinal bands of pressure and wind 111

Hadley circulation 112

Mean low-level circulation 113

Mean upper level circulation 115

Ocean circulation 116

Oceanic influences on continental hydroclimate 118

Monsoon flow 118

Tropical cyclones 119

El Niño Southern Oscillation 120

Pacific Decadal Oscillation 122

North Atlantic Oscillation 123

Water vapor in the atmosphere 123

Important points in this chapter 126

10 Formation of Clouds 128

Introduction 128

Cloud generating mechanisms 129

Cloud condensation nuclei 131

Saturated vapor pressure of curved surfaces 132

Cloud droplet size, concentration and terminal velocity 133

Ice in clouds 134

Cloud formation processes 135

Thermal convection 135

Foehn effect 136

Extratropical fronts and cyclones 138

Cloud genera 140

Important points in this chapter 141

11 Formation of Precipitation 143

Introduction 143

Precipitation formation in warm clouds 144

Precipitation formation in other clouds 146

Which clouds produce rain? 148

Precipitation form 149

Raindrop size distribution 150

Rainfall rates and kinetic energy 151

Forms of frozen precipitation 151

Other forms of precipitation 152

Important points in this chapter 153

12 Precipitation Measurement and Observation 155

Introduction 155

Precipitation measurement using gauges 156

Instrumental errors 157

Site and location errors 157

Gauge designs 160

Areal representativeness of gauge measurements 162

Snowfall measurement 165

Precipitation measurement using ground-based radar 168

Precipitation measurement using satellite systems 171

Cloud mapping and characterization 171

Passive measurement of cloud properties 172

Spaceborne radar 173

Important points in this chapter 174

13 Precipitation Analysis in Time 176

Introduction 176

Precipitation climatology 177

Annual variations 177

Intra-annual variations 177

Daily variations 180

Trends in precipitation 181

Running means 182

Cumulative deviations 183

Mass curve 184

Oscillations in precipitation 186

System signatures 187

Intensity-duration relationships 189

Statistics of extremes 190

Conditional probabilities 195

Important points in this chapter 196

14 Precipitation Analysis in Space 198

Introduction 198

Mapping precipitation 199

Areal mean precipitation 200

Isohyetal method 200

Triangle method 202

Theissen method 202

Spatial organization of precipitation 203

Design storms and areal reduction factors 205

Probable maximum precipitation 207

Spatial correlation of precipitation 209

Important points in this chapter 211

15 Mathematical and Conceptual Tools of Turbulence 213

Introduction 213

Signature and spectrum of atmospheric turbulence 213

Mean and fluctuating components 216

Rules of averaging for decomposed variables 217

Variance and standard deviation 219

Measures of the strength of turbulence 220

Mean and turbulent kinetic energy 220

Linear correlation coefficient 221

Kinematic flux 223

Advective and turbulent fluxes 225

Important points in this chapter 229

16 Equations of Atmospheric Flow in the ABL 231

Introduction 231

Time rate of change in a fluid 232

Conservation of momentum in the atmosphere 234

Pressure forces 235

Viscous flow in fluids 236

Axis-specific forces 239

Combined momentum forces 242

Conservation of mass of air 243

Conservation of atmospheric moisture 244

Conservation of energy 245

Conservation of a scalar quantity 246

Summary of equations of atmospheric flow 247

Important points in this chapter 247

17 Equations of Turbulent Flow in the ABL 248

Introduction 248

Fluctuations in the ideal gas law 248

The Boussinesq approximation 249

Neglecting subsidence 250

Geostrophic wind 251

Divergence equation for turbulent fluctuations 252

Conservation of momentum in the turbulent ABL 252

Conservation of moisture, heat, and scalars in the turbulent ABL 254

Neglecting molecular diffusion 255

Important points in this chapter 258

18 Observed ABL Profiles: Higher Order Moments 259

Introduction 259

Nature and evolution of the ABL 259

Daytime ABL profiles 261

Nighttime ABL profiles 263

Higher order moments 265

Prognostic equations for turbulent departures 265

Prognostic equations for turbulent kinetic energy 269

Prognostic equations for variance of moisture and heat 271

Important points in this chapter 276

19 Turbulent Closure, K Theory, and Mixing Length 277

Introduction 277

Richardson number 277

Turbulent closure 279

Low order closure schemes 280

Local, first order closure 281

Mixing length theory 283

Important points in this chapter 288

20 Surface Layer Scaling and Aerodynamic Resistance 289

Introduction 289

Dimensionless gradients 290

Obukhov length 292

Flux-gradient relationships 293

Returning fluxes to natural units 294

Resistance analogues and aerodynamic resistance 296

Important points in this chapter 299

21 Canopy Processes and Canopy Resistances 300

Introduction 300

Boundary layer exchange processes 301

Shelter factors 306

Stomatal resistance 308

Energy budget of a dry leaf 310

Energy budget of a dry canopy 311

Important points in this chapter 314

22 Whole Canopy Interactions 316

Introduction 316

Whole-canopy aerodynamics and canopy structure 317

Excess resistance 319

Roughness sublayer 321

Wet canopies 323

Equilibrium evaporation 325

Evaporation into an unsaturated atmosphere 327

Important points in this chapter 332

23 Daily Estimates of Evaporation 334

Introduction 334

Daily average values of weather variables 335

Temperature, humidity, and wind speed 335

Net radiation 337

Open water evaporation 339

Reference crop evapotranspiration 341

Penman-Monteith equation estimation of ERC 342

Radiation-based estimation of ERC 344

Temperature-based estimation of ERC 345

Evaporation pan-based estimation of ERC 346

Evaporation from unstressed vegetation: the Matt-Shuttleworth approach 348

Evaporation from water stressed vegetation 353

Important points in this chapter 355

24 Soil Vegetation Atmosphere Transfer Schemes 359

Introduction 359

Basis and origin of land-surface sub-models 359

Developing realism in SVATS 362

Plot-scale, one-dimensional ‘micrometeorological’ models 364

Improving representation of hydrological processes 367

Improving representation of carbon dioxide exchange 368

Ongoing developments in land surface sub-models 370

Important points in this chapter 373

25 Sensitivity to Land Surface Exchanges 380

Introduction 380

Influence of land surfaces on weather and climate 381

A. The influence of existing land-atmosphere interactions 383

1. Effect of topography on convection and precipitation 383

2. Contribution by land surfaces to atmospheric water availability 385

B. The influence of transient changes in land surfaces 385

1. Effect of transient changes in soil moisture 385

2. Effect of transient changes in vegetation cover 388

3. Effect of transient changes in frozen precipitation cover 389

4. Combined effect of transient changes 391

C. The influence of imposed persistent changes in land cover 392

1. Effect of imposed land cover change on near surface observations 392

2. Effect of imposed land-cover change on regional-scale climate 393

3. Effect of imposed heterogeneity in land cover 395

Important points in this chapter 398

26 Example Questions and Answers 404

Introduction 404

Example questions 404

Question 1 404

Question 2 405

Question 3 407

Question 4 408

Question 5 410

Question 6 411

Question 7 412

Question 8 414

Question 9 416

Question 10 418

Example Answers 418

Answer 1 418

Answer 2 420

Answer 3 420

Answer 4 425

Answer 5 426

Answer 6 427

Answer 7 429

Answer 8 432

Answer 9 434

Answer 10 437

Index 441