Impoundment Depletion: A New Hydrologic Paradigm Grounded in the Great Salt Lake Basin

Impoundments represent the largest unmeasured source of anthropogenic inflow loss to Great Salt Lake. Using satellite imagery, aerial datasets, and surface‑area‑based evaporation modeling, we quantified 478,175 acres of human‑built impoundments and 4.07 million acre‑feet of upstream reservoir storage. These structures generate 1.7–2.2 million acre‑feet of annual evaporation and 1.6–3.2 million acre‑feet of non‑return storage, exceeding the combined depletion attributed to agricultural, municipal, and industrial use. Sectoral accounting frameworks that begin measurement after storage and conveyance omit these losses, obscuring the dominant role of impoundments in reducing lake inflows. Because the Great Salt Lake is endorheic, upstream evaporation and long‑term storage translate directly into diminished lake elevation, revealing the full hydrologic cost of impoundment growth. Integrating reservoir evaporation, non‑return storage, agricultural evapotranspiration, and mineral extraction into a unified depletion budget provides a more accurate basis for management and for understanding the lake’s decline. These findings highlight the need for basin‑scale accounting approaches that reflect the complete hydrologic footprint of human infrastructure in closed and water‑limited systems.