Theme for 2005:
Precipitation and Flood Forecasting in the American River Basin

Engineering Climatology for California

This project started fifty years ago when there was much confusion in assigning return periods to extreme rainfall events. This resulted in chaotic variation in design storms due to small sample size and much controversy regarding choices in frequency distributions. There was a need for procedures where all workers would achieve similar results when analyzing small samples of rainfall records that were located near project sites. This earlier confusion led to a regional approach in rainfall studies.

It became apparent that this archive is also a history of our times and very much worthy of serious consideration as historic record. The interesting part of this activity for me has been the analysis of historic trends in all of the various time series data sets.

Validation and Sensitivities of Dynamic Precipitation Simulation for Winter Events over the Folsom Lake Watershed: 1964-1999

A number of sensitivity runs were performed to understand dependence of model precipitation on boundary and initial fields, cold vs. warm start, and microphysical parameterization. The principal findings of the validation analysis are: (a) the MM5 model achieves a good percentage bias score of 103% in simulating Folsom basin MAP when compared to MAP derived from dense precipitation gauge networks; (b) spatial grid resolution higher than 9 km is necessary to reproduce the spatial MAP pattern among sub-basins of the Folsom basin; (c) the model performs better for heavy than for light and moderate precipitation. The analysis also showed significant simulation dependence on the spatial resolution of the boundary and initial fields and on the microphysical scheme used.

Understanding the Sierra Nevada Hydrologic Response to Climate Change

• Changes in temperature, precipitation, streamflow
• Changes in snow accumulation and snow melt
• Distributions by month, elevation, and latitude
• Timing of the cumulative annual streamflow
• Annual peak flow exceedance probabilities
• Temperature, Heat and Mortality Analysis
• Precipitation and Snowpack Projections
• Sea Level Projections and Impacts
• Projected Vegetation Distributions

A Long-Term (50-yr) Historical Perspective on the Meteorology and Hydrology of Flood-Generating Winter Storms in the American River Basin

In this talk, 50-yr long daily chronologies of these transports will be used to identify (a) storms that yield particularly large amounts of low-altitude (rainy) precipitation and (b) the notably warm and intense pineapple-express storms. This long-term perspective reveals that, historically, tropical El Nino conditions have favored enhancements of low-altitude precipitation which, falling most often as rain rather than snow, tends to increase flood risks. Pineapple-express patterns, on the contrary, appear to be favored by nearneutral (non-El Nino) tropical conditions during El Nino-rich decades (warm phases of the Pacific Decadal Oscillation). The resulting chronologies of these events, plus events that might have resulted in floodgenerating storms but did not, help put the risks from such storms into perspective. Some hints as to the future of these storms can be gathered by applying similar approaches to recent climate-change projections.

Evaluate the Snow Depletion Curve Theory in the American River Basin with Distributed Snow Model

Using Synoptic Climatology and the PRISM Model to Improve Precipitation Assessment and Prediction

Hydrologic Forecasting on the American River

Previously the American River watershed was modeled as four sub-basins, and the model only calculated full natural flow into Folsom reservoir. During the most recent recalibration, the watershed was divided into nine sub-basins in order to include simulations of inflow into the four largest reservoirs (French Meadows, Hell Hole, Loon Lake, and Union Valley). By simulating the upstream reservoirs, the new model is better able to forecast actual inflows into Folsom reservoir.

Calibration of the new American River watershed model was performed for the period of record of October, 1989, through September, 1999. Full natural flow computations were designed so that they would reflect the operational FNF calculations performed by DWR. Statistical analysis on the model's simulated FNF showed an overall improvement in performance, both for water supply forecasting and flood forecasting.

This presentation will focus primarily on model performance during the most recent high flow event (January 1–3, 1997). Simulations of both full natural flow and actual inflow to Folsom Reservoir will be examined, and areas for future improvement in the modeling system will be proposed. Finally, an explanation of operational forecast products will be presented.

NOAA Efforts to Improve Precipitation and Flood Forecasting by Studying American River

The HMT program is being developed for the purpose of advancing water resources data assimilation. The general strategy of this effort is to conduct research and development to deploy advanced systems for observed information to support critical decision making for flood mitigation, hydropower energy generation, water resources control, and fisheries management. More specifically, high resolution atmospheric and hydrometeorologic observations (precipitation, soil moisture, snowpack, winds, temperature, and moisture) will be collected and analyzed for several key water resource applications such as distributed hydrologic model validation, quantitative precipitation forecast (QPF), and estimation (QPE) validation.

DMIP 2 continues the work begun under DMIP 1 to conduct research into advanced hydrologic models for river and water resources forecasting. Twelve groups from the hydrologic research community participated in DMIP 1, resulting in a wealth of knowledge for the scientific community and valuable guidance for the National Weather Service (NWS) research program. DMIP 2 is designed around two themes: 1) continued investigation of science questions pertinent to the DMIP 1 test sites, and 2) distributed and lumped model tests in hydrologically complex basins in the mountainous Western US.