Hydrological drought characteristics

In this chapter, you will find an overview of the most used hydrological drought characteristics and their derivation. This includes single low flow indices, such as percentiles from the flow duration curve; drought deficit characteristics derived by the threshold level method, such as duration and deficit volume, standardised indices, such as the Standardised Groundwater Level Index, multivariate indices based on modelling or a combination of ‘stand alone’ indices, and spatial drought indices. We explain methods of calculation in terms of both time series and single indices and give examples of how to derive different indices through worked examples. The methods described are applicable for both observed and simulated time series of hydrological variables representing a flux, such as river flow, or a state variable, such as groundwater levels. We also give general recommendations for the choice of index based on the problem under study, data availability and climatic and regional characteristics. Finally, we describe the relationship between different drought indices.