Streamflow Droughts

Drought is a natural disaster with recurring characteristics which has a severe consequence, that is, it affects every sector of the society and therefore there is a need to characterise or define the occurrence, severity and impact of a drought. In literature, the term drought is defined as a prolonged period of below-normal precipitation that leads to reduced streamflow and water availability in rivers, lakes, and groundwater system. Droughts are generally classified as meteorological, hydrological, agricultural, and socio-economic droughts, occurring in a sequential manner. Hydrological drought, also called streamflow drought, refers to the reduction in water levels and flow rates in rivers, streams, reservoirs, and groundwater caused by prolonged precipitation deficits. Streamflow drought is commonly analysed using indices such as the streamflow drought index (SDI) or the threshold level drought index. Estimation of streamflow drought is essentially a study of the characteristics of the drought indicator, the streamflow time series. Drought indicators need to be characterised, quantified and converted to usable information such as low flow and drought indices.