State Water Resources Control Board demonstrates open-source LSPC watershed modeling to support drought planning

State Water Resources Control Board staff demonstrated an open-source hydrologic modeling workflow designed to give state and local water managers a consistent baseline for planning and drought response.

"I'm a program manager for our supply and demand assessment program," said Philip Denton, introducing the project and its aim to pair calibrated Loading Simulation Program in C++ (LSPC) models with cleaned diversion data to show where water is available and who is using it. Denton said the program produces data and tools intended to inform "efficient, equitable water allocations" during shortages.

Peter Haupp, an environmental scientist in the Division of Water Rights, walked through the technical approach used to simulate daily streamflow at subbasin outlets. He said the LSPC model integrates three major output components—surface runoff, shallow subsurface interflow, and active groundwater (baseflow)—and produces daily time series across each subbasin to fill gaps where gauges are sparse. "LSPC gives us a consistent way to understand how flow conditions and natural water availability across the entire watershed," Haupp said.

Staff described the inputs the models rely on: local gauge observations, the NLDAS gridded weather dataset, and PRISM climate interpolations to capture spatial patterns, plus GIS layers for land cover, slope, and soils. Haupp said those inputs let the model simulate how forest, grassland, vineyards, and developed areas handle water differently and help calibrate results against USGS stream gauges.

On the demand side, Denton said the program is reconciling self-reported surface-water diversion records from the board’s reporting system, cleaning units, removing duplicates, and creating monthly demand patterns. He noted that data currently lives in ERIMS and will soon be available in Cal Waters.

The board said it has executed a $15,000,000 modeling contract with Paradigm Environmental to expand an approach piloted in the Russian River to new watersheds. Staff named three initial pilot watersheds—Butte Creek, Napa and the Navarro—and said the program will expand to 18 watersheds focused where surface-water demand and ecological importance (for example, salmon habitat or known low-flow conditions) are high.

Staff emphasized that the outputs and tools will be open source and publicly available. A draft model development report is available for public review, and staff said Paradigm will update model runs based on feedback. Denton told attendees the session would be recorded and posted and that staff will notify subscribers when draft reports and tools are published.

The technical demonstration continued with practical sessions planned to show participants how to download LSPC, run simulations, perform calibration and validation, read hydrographs, and run scenario tests for land-use, climate, or reservoir changes. The presentation was handed off to Marshall Knott to continue.