Note: Front Cover -- Hydrological Drought -- Hydrological Drought Processes and Estimation Methods for Streamflow and Groundwater -- Copyright -- Brief contents -- Contents -- Contents on GitHub1 -- 1. Data -- 2. Worked examples -- 3. Self-guided tours -- 4. Supporting documents -- 5. Supporting code -- List of contributors -- Preface -- Acknowledgements -- Glossary -- Introduction -- Drought-related terms and description -- REFERENCES -- Abbreviations, symbols and catchment descriptors -- Abbreviations -- Symbols -- Catchment descriptors as used in Chapter 8 -- I - Drought as a natural hazard -- 1 - Introduction -- 1.1 Scope -- 1.2 Hydrological drought -- 1.3 The drought hazard -- 1.4 International low flow and drought studies -- 1.5 Outline -- 1.6 Further reading -- References -- bksec2_1 -- 2 - Hydroclimatology∗ -- 2.1 Introduction -- 2.2 Drought in different climates -- 2.2.1 Global atmospheric circulation -- 2.2.2 Hydrology and drought in the world's climate zones -- 2.2.2.1 A-climates -- 2.2.2.2 B-climates -- 2.2.2.3 C-climates -- 2.2.2.4 D-climates -- 2.2.2.5 E-climates -- 2.2.3 Atmospheric circulation and drought -- 2.2.3.1 Regional atmospheric causes -- 2.2.3.2 Large-scale atmospheric causes -- 2.2.3.3 Coupled ocean-atmosphere causes -- 2.3 Drought initiation and termination -- 2.3.1 From meteorological anomaly to hydrological drought -- 2.3.2 Drought termination -- 2.4 Space-time variability -- 2.4.1 Spatial variability -- 2.4.2 Temporal variability -- 2.5 Climate change and drought -- 2.5.1 Observed climate change -- 2.5.2 Future climate change -- 2.6 Summary -- 2.7 Further reading -- References -- bksec2_10 -- 3 - Drought-generating processes∗ -- 3.1 Introduction -- 3.2 Catchment water balance -- 3.3 Soil system - unsaturated zone -- 3.3.1 Introduction -- 3.3.1.1 Actual evapotranspiration -- 3.3.1.2 Soil infiltration. , 3.3.1.3 Groundwater recharge -- 3.3.2 Effects on the water balance -- 3.3.2.1 Low precipitation -- 3.3.2.2 High potential evapotranspiration -- 3.3.3 Variability in evapotranspiration and groundwater recharge as simulated for two contrasting catchments -- 3.3.3.1 Evapotranspiration deficit in two different climates -- 3.3.3.2 Groundwater recharge in two different climates -- 3.3.4 Influence of soil characteristics, land use and water-table depth on actual evapotranspiration and groundwater recharge -- 3.3.4.1 Soil characteristics -- 3.3.4.2 Land use -- 3.3.4.3 Water-table depth -- 3.4 Groundwater system - saturated zone -- 3.4.1 Groundwater levels -- 3.4.1.1 Groundwater levels in different hydrogeological settings and climates -- 3.4.2 Groundwater flow systems and groundwater discharge -- 3.4.2.1 Flow systems -- 3.4.2.2 Groundwater discharge -- 3.4.3 Spring flow -- 3.5 Surface water system -- 3.5.1 River flow generation -- 3.5.1.1 Overland flow and total river flow -- 3.5.1.2 Throughflow -- 3.5.1.3 Surface water network -- 3.5.1.4 River flow -- 3.5.2 Lakes and wetlands -- 3.5.2.1 Influence of lakes on downstream flow in two contrasting climates -- 3.5.2.2 Wetlands -- 3.6 Hydrological drought in cold climates -- 3.7 Drought typology -- 3.8 Summary -- 3.9 Further reading -- References -- bksec2_10 -- II - Estimation methods -- 4 - Hydrological data∗ -- 4.1 Introduction -- 4.2 Definitions and concepts -- 4.2.1 What is meant by 'data'? -- 4.2.2 Time series data -- 4.2.3 Spatial data -- 4.2.4 Metadata -- 4.2.5 Importance of scale: spatial and temporal -- 4.2.6 Uncertainty -- 4.3 Data for hydrological drought -- 4.3.1 River level data -- 4.3.2 Rating curves and spot gaugings -- 4.3.2.1 Spot gaugings -- 4.3.2.2 Rating curves -- 4.3.2.3 Factors affecting the stage-discharge relation -- 4.3.3 Continuous river flow measurements. , 4.3.3.1 Velocity-area gauging stations -- 4.3.3.2 Weirs and flumes -- 4.3.3.3 Acoustic gauging stations -- 4.3.4 Other sensing technologies -- 4.3.5 Measurement challenges at low flow -- 4.3.6 Groundwater level data -- 4.3.6.1 Automatic recording of groundwater levels -- 4.3.6.2 Manual groundwater level monitoring -- 4.3.6.3 Estimating groundwater recharge -- 4.3.6.4 Monitoring groundwater discharge -- 4.3.6.5 Groundwater storage -- 4.3.7 Quality control -- 4.3.7.1 The nature of errors -- 4.3.7.2 Good practice -- 4.3.7.3 Data validation -- 4.3.7.4 Missing data -- 4.3.8 Supporting hydrometeorological time series data -- 4.3.8.1 Precipitation -- 4.3.8.2 Evaporation -- 4.3.8.3 Soil moisture -- 4.3.9 Human interventions -- 4.3.9.1 Flow naturalisation -- 4.4 Spatial and large-sample datasets -- 4.4.1 Local-scale data -- 4.4.2 Regional to global scale data -- 4.4.2.1 Large-scale physiographic data -- 4.4.2.2 Large-sample hydrological data -- 4.4.2.3 Large-scale hydrological data -- 4.4.2.4 Large-scale climatological data -- 4.4.2.5 Satellite data -- 4.4.3 Spatial data access -- 4.4.3.1 Data catalogues -- 4.4.3.2 Data access -- 4.4.3.3 Spatial data sharing, integration and dissemination -- 4.5 Example datasets -- 4.5.1 International Dataset -- 4.5.2 Regional Dataset of Eastern Austria -- 4.5.3 Local datasets -- 4.5.3.1 Upper-Guadiana catchment (Spain) -- 4.5.3.2 The Stonor Park well, Henley on Thames (UK) -- 4.6 Summary -- 4.7 Further reading -- References -- bksec2_22 -- 5 - Hydrological drought characteristics∗ -- 5.1 Introduction -- 5.2 Drought terminology -- 5.3 Low flow characteristics -- 5.3.1 Percentiles from the flow duration curve -- 5.3.2 Mean annual minimum flow -- 5.3.3 Base flow indices -- 5.3.3.1 The Base Flow Index -- 5.3.4 Recession indices -- 5.3.4.1 Analytical expression -- 5.3.4.2 Derivation of a characteristic recession. , 5.4 Drought deficit characteristics -- 5.4.1 Threshold level method -- 5.4.1.1 Threshold selection -- 5.4.1.2 Time resolution -- 5.4.2 Indices for intermittent and ephemeral rivers -- 5.4.2 Indices for intermittent and ephemeral rivers -- 5.4.3 The sequent peak algorithm -- 5.5 Standardised indices -- 5.5.1 Empirical quantiles -- 5.5.2 Standardised (to the normal distribution) indices -- 5.6 Multivariate indices -- 5.6.1 Modelled indices -- 5.6.2 Combined indices -- 5.7 Spatial drought characteristics -- 5.7.1 Examples of non-contiguous drought area approach -- 5.7.2 Examples of contiguous drought area approach -- 5.7.3 Drought tracking -- 5.8 Application at large scale -- 5.9 Relationship between indices -- 5.9.1 Ranks and correlation coefficients -- 5.10 Summary -- 5.11 Further reading -- References -- bksec2_16 -- 6 - Frequency analysis∗ -- 6.1 Introduction -- 6.2 Basic probability concepts -- 6.2.1 Populations -- 6.2.2 Samples -- 6.3 Data for extreme value analysis -- 6.3.1 Basic assumptions -- 6.3.2 Selection of extreme events -- 6.3.2.1 Annual maximum or minimum series -- 6.3.2.2 Partial duration series -- 6.3.2.3 r-Largest events -- 6.3.2.4 Outliers -- 6.3.3 Minimum values -- 6.3.4 Maximum values -- 6.4 Probability distributions -- 6.4.1 Extreme value distributions -- 6.4.2 The Generalised Extreme Value distribution -- 6.4.3 The Generalised Pareto distribution -- 6.4.4 Other distributions -- 6.4.4.1 The log-Normal distribution -- 6.4.4.2 The Pearson type 3, Gamma and log-Pearson type 3 -- 6.4.5 Mixed distributions -- 6.4.6 Selection of distribution function -- 6.5 Estimation methods -- 6.5.1 Method of moments -- 6.5.1.1 Product moments -- 6.5.1.2 L-moments -- 6.5.2 Maximum likelihood estimators -- 6.5.3 Estimation of design values, uncertainties and risk -- 6.5.4 Non-stationary frequency analysis -- 6.6 At-site frequency analysis. , 6.6.1 Low flow characteristics -- 6.6.2 Deficit characteristics -- 6.7 Regional frequency analysis -- 6.7.1 Regional estimation model -- 6.7.2 L-moment analysis -- 6.7.2.1 L-moment ratio diagrams -- 6.7.2.2 Test of regional homogeneity -- 6.7.2.3 Determination of a regional distribution -- 6.7.3 Generalised least squares regression -- 6.7.3.1 Estimation of index parameter by combining regional and site-specific data -- 6.7.4 Delineation of homogeneous regions -- 6.7.5 Self-guided tour: Regional frequency analysis -- 6.8 Severity-area-frequency curves -- 6.9 Summary -- 6.10 Further reading -- References -- bksec2_24 -- 7 - Statistical analysis of drought series∗ -- 7.1 Introduction -- 7.2 Time-series modelling -- 7.2.1 A simple Gaussian random model -- 7.2.2 Theory of runs -- 7.2.3 Autoregressive modelling and simulation -- 7.2.4 An observed time series of annual discharge -- 7.2.5 Applying and expanding autoregressive models -- 7.3 Regression -- 7.3.1 Linear regression -- 7.3.2 Correlation -- 7.3.3 Multiple linear regression -- 7.3.4 Goodness of fit, calibration and understanding residuals -- 7.3.5 Variable selection -- 7.3.6 Model validation -- 7.3.7 Generalised linear models -- 7.3.7.1 Logistic regression -- 7.3.7.2 Poisson regression -- 7.3.7.3 Gamma regression -- 7.3.8 A note about causality -- 7.4 Trend analysis -- 7.4.1 Linear trends -- 7.4.2 Non-parametric trend analysis -- 7.4.3 Structural change analysis -- 7.5 Spatio-temporal analysis -- 7.5.1 Grid-based correlation -- 7.5.2 Composite analysis -- 7.5.3 Principal component analysis -- 7.5.4 Cluster analysis -- 7.5.5 Canonical correlation analysis -- 7.6 Novel methods -- 7.7 Summary -- 7.8 Further reading -- References -- 8 - Regionalisation procedures - estimation at the ungauged site∗ -- 8.1 Introduction -- 8.2 Physiographic similarity -- 8.2.1 Similarity indices. , 8.2.1.1 River flow similarity.