What are drought Severity-Duration-Frequency (SDF) curves?
In short: drought Severity-Duration-Frequency (SDF) curves summarize, for a location, how drought severity relates to its duration and its return period (frequency) — the drought analogue of rainfall Intensity-Duration-Frequency (IDF) curves. They let you estimate how severe a drought of a given duration is likely to be for a chosen return period, which is useful for water-resource planning. DMAP V2.1 builds Severity-Duration-Frequency relationships within its drought-severity window.