What the La Niña years left behind.
A drought is a debt: every month of below-normal rain adds to it, and reservoirs, soils and groundwater carry it forward. The Pacific spent most of 2020–2025 in La Niña. This route adds up what each county owes, or in the wet places has banked, since then, and asks the question a record El Niño raises: how much of it has a strong El Niño winter ever paid back?
How the debt is counted
For each county, NOAA's nClimDiv monthly precipitation minus that calendar month's 1991–2020 normal, added up from the start month to the latest month. Negative is drought debt, positive is a pluvial surplus. "Months of rain" divides the total by an average month's normal. The Palmer Hydrological Drought Index (PHDI) is NOAA's slow-moving drought index: it tracks the water that soils, groundwater and reservoirs remember, not just the latest rain. Repayment compares the debt with the Nov–Mar precipitation departure in each of the 9 strong El Niño winters since 1957: the median, and the best and worst of them. One winter's rain is not the same as refilled reservoirs, so read repayment as an upper bound on relief.