DSDI: stands for Demand Sensitive Drought Index. Refer to the INTRO panel for a detailed description!
Cumulative Deficit: The deficit (Demand-Supply) cumulated over the entire period of analysis [cumulated when positive; set to zero when negative].
Drought Event: A part of the cumulative deficit curve above the zero line constitutes a drought event.
Threshold Concept: While in many drought studies they adopt a threshold to define a drought event, we do not consider the threshold approach to define drought events in this research. The zero line is the basis to define a drought event. However, the approach can be implemented by considering the reserve at the location (total water store) as baseline.
Drought Attributes: We define four attributes for a drought event: Onset, Duration, Severity, and Recovery. The onset of the drought event is the point in time where the deficit begins (greater than zero). The Duration is the period from the onset to the maximum deficit; the maximum deficit is the severity; and the period from the maximum deficit until the cumulated deficit drop back to zero is the recovery.
Worst Drought: The worst drought can be defined in terms of its Duration, its severity, or its Recovery time. It is the drought event with the highest value of the considered attributes.
NDC, NDImax: The Normalized Deficit Cumulated (NDC) index capture droughts resulting from deficits carried over years (multi-year droughts), and athe NDImax capture within year droughts. There are both computed as the ratio of the maximum deficit to the average precipitation received by the location over the period of analysis. NDC<1 indicates that the location receives on average enough rainfall to cover its deficit. NDC>1 means the amount of rainfall is not sufficient. The location is then dependent on other water sources to meet the demand.
Resiliency: the probability of recovery from failure is termed as Resiliency (or the recovery rate). It indicates how often drought events are fully recovered. It is computed as the ratio of the number of drought events to the total duration time of all events. A county with a higher Recovery Rate compare to another has a greater resiliency to drought. Droughts in this county recovers often and do not last for long.
Relative Recovery: We define the relative recovery as the expected value of the ratio of the drought recovery time to the drought duration time. If the recovery rate < 1 drought events recover quicker than they last (in average).