Development of Western United States pluvioregions for post-wildfire assessments

The U.S. Geological Survey (USGS) National Water Quality Program, through the Prototyping Modeling and Assessment of Post-wildfire Water Availability project, aims to enhance the ability to assess and predict the impacts of wildfires on water supplies. Precipitation is a key driver of flooding, debris flows, and water quality responses following wildfire. The intensity, duration, and seasonality of precipitation can be used to delineate regions of similarity that provide a schema to classify post-wildfire hydrologic and associated water quality responses. We use the term “pluvioregion” here to define the classification of various precipitation characteristics into regions of commonality. Developing pluvioregions requires surmounting numerous challenges, including robust cluster classification and selection of precipitation characteristics . For instance, while conventional clustering methods are effective for identifying broad patterns, they may overlook subtle but significant differences among locations assigned to the same group. In this analysis, we employ traditional classification tools (i.e., k-means clustering and Principal Components Analysis) as well as archetypal analysis to establish pluvioregions for over 4.7 million locations in the western United States, using several precipitation regime features to improve predictions of post-wildfire water quality. Five main attributes were used to define pluvioregions: (i) 2-year recurrence of 6-hour rainfall intensity, (ii) ratio of 2-year recurrence, 24-hour to 6-hour rainfall intensity, (iii) precipitation concentration index, (iv) snow persistence, and (v) aridity index. Our optimization process identified five distinct pluvioregions (“Interior Mountains,” “Arid Interior,” “Pacific Northwest Mountains,” “Pacific Southwest Coast,” and “Southwest/Great Plains”). We also include many monthly and annual climate metrics. These defined pluvioregions provide a basis for future studies, evaluations, and modeling of hydrologic and water quality risks following wildfires.

This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.
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