Normalizing rainfall/debris-flow thresholds along the U.S. Pacific coast for long-term variations in precipitation climate
By: Raymond C. Wilson
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Abstract
Broad-scale variations in long-term precipitation climate may influence rainfall/debris-flow threshold values along the U.S. Pacific coast, where both the mean annual precipitation (MAP) and the number of rainfall days (#RDs) are controlled by topography, distance from the coastline, and geographic latitude. Previous authors have proposed that rainfall thresholds are directly proportional to MAP, but this appears to hold only within limited areas (< 1?? latitude), where rainfall frequency (#RDs) is nearly constant. MAP-normalized thresholds underestimate the critical rainfall when applied to areas to the south, where the #RDs decrease, and overestimate threshold rainfall when applied to areas to the north, where the #RDs increase. For normalization between climates where both MAP and #RDs vary significantly, thresholds may best be described as multiples of the rainy-day normal, RDN = MAP/#RDs. Using data from several storms that triggered significant debris-flow activity in southern California, the San Francisco Bay region, and the Pacific Northwest, peak 24-hour rainfalls were plotted against RDN values, displaying a linear relationship with a lower bound at about 14 RDN. RDN ratios in this range may provide a threshold for broad-scale regional forecasting of debris-flow activity.
Suggested Citation
Wilson, R.C., 1997, Normalizing rainfall/debris-flow thresholds along the U.S. Pacific coast for long-term variations in precipitation climate, in International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment, Proceedings, San Francisco, CA, USA, 7 August 1997 through 9 August 1997, p. 32-43.
| Publication type | Conference Paper |
|---|---|
| Publication Subtype | Conference Paper |
| Title | Normalizing rainfall/debris-flow thresholds along the U.S. Pacific coast for long-term variations in precipitation climate |
| Year Published | 1997 |
| Language | English |
| Publisher | ASCE |
| Publisher location | New York, NY, United States |
| Larger Work Title | International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment, Proceedings |
| First page | 32 |
| Last page | 43 |
| Conference Title | Proceedings of the 1997 1st International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment |
| Conference Location | San Francisco, CA, USA |
| Conference Date | 7 August 1997 through 9 August 1997 |