What is the Moisture Deficit Index (MDI)?
In short: the Moisture Deficit Index (MDI) is a drought index that measures the shortfall between water supply and atmospheric water demand — essentially the deficit between precipitation and potential (or actual) evapotranspiration accumulated over a period. Larger deficits indicate drier, more drought-stressed conditions. Because it accounts for evaporative demand, the MDI reflects agricultural and meteorological drought better than precipitation-only indices in warm or variable climates. DMAP V2.1 calculates the Moisture Deficit Index among its 19 drought indices.