California Water Science Center

Development of Precipitation-Runoff Modeling System (PRMS) for the Tuolumne River Basin, Central California, with application for streamflow predictability and flood forecasting.

Location of study area: Tuolomne River Basin

Location of study area: Tuolomne River Basin

Runoff from snowmelt and rainfall in the Tuolumne River basin plays a significant role in irrigation and domestic water supply for Turlock and Modesto Irrigation Districts, City of Modesto and the San Francisco Bay Area. This area experiences very different seasonal and decadal climate events which are known to affect the timing and volumes of runoff. Land-cover change alone, such as the Rim Fire of 2013, may alter the basinís hydrology and streamflows. Existing models cannot adequately describe responses to changing land cover and climate which affect snow accumulation or melt in winter, the timing and volumes of streamflows, and the availability of snowpack for spring melt. A better understanding of streamflow variation in this basin is necessary for improved reservoir operations and watershed management.

A spatially detailed Precipitation-Runoff Modeling System (PRMS), and Object User Interface (OUI) will be constructed and calibrated for the Tuolumne River Basin. PRMS simulates responses to land cover and climate variations at a higher spatial resolution than is currently available to DWR. The calibrated Tuolumne PRMS will be used to test how the basin streamflows respond to changing land cover and climate, by inputting historical and synthesized parameter settings and data projections into the PRMS model. By applying the calibrated model, the questions this study will address are: (1) How will a change in land cover effect inflows to the basinís reservoirs? (2) How will a change in climate effect reservoir inflows? (3) How will a combined change in land cover and climate effect reservoir inflows?

This study will provide an analysis tool for forecasting seasonal and longer term streamflow variations, and for evaluating land cover and climate variations in the Tuolumne River Basin. This study will directly or indirectly address several water-resource issues identified in the USGS Science Strategy document (USGS, 2007): drinking water availability, the suitability of aquatic habitat for biota (by providing forecasted streamflow simulations), hydrologic hazards (flooding), hydrologic system management, and effects of climate and land cover alterations on water resource management. This work will develop tools relevant to CAWSC science issues that underlie the management of watershed and hydrologic hazards, and address the USGS focus on land cover and climate change studies.

Specific tasks are: 1) collect relevant spatial and temporal data, including natural streamflows to be used for calibrations, assemble and manage data in a GIS, and analyze data to understand the physical system of the watershed, 2) construct the Tuolumne PRMS model by delineating model area and hydrologic response units (HRUs), estimating parameters, and calibrating, 3) build the object user interface (OUI), 4) release calibrated Tuolumne PRMS and OUI to DWR for operational trials, and 5) assess the basinís response to land cover and climate change utilizing the Tuolumne PRMS.

Cooperating Agency: California Department of Water Resources, Hydrology and Operations Office
Cooperating Agency: California Department of Water Resouces, Division of Flood Management
Project Chief: Kathryn M. Koczot
Phone: 619-225-6152

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