Reference

Glossary

The terms the brief uses, defined the way an operator would say them.

Acre-foot (af): The volume of water covering one acre to a depth of one foot, about 326,000 gallons. The standard unit for reservoir storage and allocations in the western US. Large storage is often given in millions, written "3.76M af".
Allocation: The share of contracted water a project tells its contractors they can expect this year, stated as a percentage of contract amount. Set and revised by the operating agency. We report allocations as announced; we do not forecast them.
Carryover: Water held in storage at the end of one water year to be available in the next. High carryover into a dry year is a buffer; low carryover is exposure. The water year runs October 1 to September 30.
Central Valley Project (CVP): The federal water project in California operated by the US Bureau of Reclamation. Serves agricultural, urban, and wildlife-refuge contractors, anchored by Shasta, Trinity, Folsom, New Melones, Millerton, and San Luis.
State Water Project (SWP): California's state-operated water project, run by the Department of Water Resources, anchored by Oroville. Distinct from the CVP; the two share some Delta infrastructure and coordinate operations.
Drought Severity and Coverage Index (DSCI): A single number from 0 to 500 that rolls up the US Drought Monitor's five drought classes (D0 abnormally dry through D4 exceptional drought) across an area, weighting more severe classes more heavily. Higher means more widespread and more severe drought.
Hydrologic Unit Code (HUC): The USGS numbering system for watersheds, nested from two-digit regions down to finer subbasins. We use it to roll reservoirs and gauges up to a basin.
Versus the 5-year median (vs-5yr-median): A series compared against the median value for the same calendar period over the prior five years. Our standard "is this normal" yardstick. "Below the 5-year median" always traces to a computed figure, never a gut sense of normal.
Storage: The volume of water currently held behind a dam, in acre-feet. The core reservoir signal. Drawdown is the seasonal or operational release that lowers it; refill is the spring runoff that raises it.
Streamflow / discharge: The volume of water passing a gauge per unit time, in cubic feet per second (cfs). Reported by USGS at basin-representative gauges.