Probable Maximum Precipitation depths were developed for the states of Colorado and New Mexico and surrounding regions. This covered thousands of dams, many of which are classified as high hazard. The States of Colorado and New Mexico present unique challenges when it comes to extreme rainfall. Terrain varies from the lower plains to the highest elevations of the Rocky Mountains and back down to the Colorado Plateau and canyon country. Each of these regions had to be represented appropriately during the Regional Extreme Precipitation Study where AWA developed updated PMP depths from the two-state region. This was a collaborative effort that included public-private partnership and several parallel tasks and areas of expertise. AWA PMP depths replaced those from Hydrometeorological Reports 49, 51, and 55A, adding more than 50 years of additional data and PMP development techniques. This included several new storms analyses and a unique reanalysis process that involved model reanalysis of past extreme storm events. A description of this process can be found in the Bulletin of the American Meteorological Society here. All PMP depths and storm analyses outputs were calculated on a gridded basis and provided in AWA’s PMP tool. This allows for explicit calculations of PMP/PMF for any location within the entire region from a single point through the entire study domain. PMP depths for durations from 1-hour through 72-hours and included storm specific temporal patterns.
In comparison to the NWS Hydrometeorological Reports 51 and 55A, the new study provides:
- Reproducible Results
- Gridded dataset within GIS platform relies on computer analysis versus human interpretation of contours
- Included 50 years of new data that resulted in including several new storms for analysis that were not accounted for in the HMRs
- PMP results island-wide
- Includes temporal distributions
- Includes gridded rainfall data for mode calibration
The new PMP estimates are available for the entire region, down to a single grid level. This information allows for hydrologic analyses to be completed for any location and for all durations.
When compared to previous PMP depths, the updated values from this study resulted in a wide range of reductions for most basin sizes and storm durations, with some regions resulting in minor increases. PMP depths are highest along the Balcones Escarpment and the Gulf Coast where Hurricane landfall affects the region. These spatial variations in PMP depth, match the general weather patterns of the region related to moisture availability, topography, and storm dynamics.
Data, assumptions, and analysis techniques used in this study have been reviewed and accepted by the by an independent board of reviewers, as well as study participants from both the Colorado and New Mexico dam safety groups, FERC, NWS ESRL, NRC, USGS, and NRCS.