Recent Updates to NOAA/NWS Rainfall Frequency Atlases Geoff Bonnin Hydrometeorological Design Studies Center Office of Hydrologic Development NOAA’s National Weather Service Geoff Bonnin Hydrometeorological Design Studies Center Office of Hydrologic Development NOAA’s National Weather Service

Topics What Are Rainfall Frequency Estimates? Why is NWS Involved? What is NWS Doing? Products and Delivery New Technology Discussion What Are Rainfall Frequency Estimates? Why is NWS Involved? What is NWS Doing? Products and Delivery New Technology Discussion

Rainfall Frequency Estimates? Climatological variability of heavy rainfall –i.e. the 1 in 100 year 60 minute rainfall for Las Vegas airport is 1.5 inches Federal, state and local governments –embedded in regulations Used for designs that deal with water –storm water drainage, ponds, culverts, highway bridges, building roofs, fish and bird habitats, etc Fresh water pollution discharge analysis –EPA Clean Water Act (NPDES) Climatological variability of heavy rainfall –i.e. the 1 in 100 year 60 minute rainfall for Las Vegas airport is 1.5 inches Federal, state and local governments –embedded in regulations Used for designs that deal with water –storm water drainage, ponds, culverts, highway bridges, building roofs, fish and bird habitats, etc Fresh water pollution discharge analysis –EPA Clean Water Act (NPDES)

Why is NWS Involved? Early 1950s –NWS nominated to make rainfall climatology estimates for use in design standards –nominated by other Federal water agencies –NWS is independent 1953; U.S. Weather Bureau Technical Paper 24 De-facto National Standards –referenced in federal, state, and local regulations –traditional civil works to environmental management Performed At Request Of And Funded By Users –not from NWS budget Early 1950s –NWS nominated to make rainfall climatology estimates for use in design standards –nominated by other Federal water agencies –NWS is independent 1953; U.S. Weather Bureau Technical Paper 24 De-facto National Standards –referenced in federal, state, and local regulations –traditional civil works to environmental management Performed At Request Of And Funded By Users –not from NWS budget

Documents Are Getting Old 5 – 60 minutes1 – 24 hours2 – 10 days Western U.S.Frederick & Miller (1979) Arkell & Richards (1986) NOAA Atlas 2 (1973) Tech Paper 49 (1964) AZ, NE, NM, UT, southeast CA NOAA Atlas 14 (2003) NOAA Atlas 14 (2003) NOAA Atlas 14 (2003) Eastern U.S.Tech Memo 35 (1977) Tech Paper 40 (1961) Tech Paper 49 (1964) HawaiiTech Paper 43 (1962) Tech Paper 43 (1962) Tech Paper 43 (1962) AlaskaTech Paper 47 (1963) Tech Paper 47 (1963) Tech Paper 52 (1965) Puerto RicoTech Paper 42 (1961) Tech Paper 42 (1961) Tech Paper 53 (1965)

What is NWS Doing?

Precipitation Frequency Estimates Durations: 5 minutes to 60 days Return Periods: 2 to 1000 years High Resolution Spatial Estimates –30 arc second Durations: 5 minutes to 60 days Return Periods: 2 to 1000 years High Resolution Spatial Estimates –30 arc second

Products & Delivery Web Based Delivery –“Precipitation Frequency Data Server” –response is very favorable High Quality Maps Produced Using GIS Interactive Tables and Charts Base Grids Seasonality Areal Reduction Factors Temporal Distributions Documentation Web Based Delivery –“Precipitation Frequency Data Server” –response is very favorable High Quality Maps Produced Using GIS Interactive Tables and Charts Base Grids Seasonality Areal Reduction Factors Temporal Distributions Documentation

Precip Frequency Data Server buildout.perl.html

Much More Data Average Record Length over 50 Years –over double ≈ 1,500 Daily Stations in Southwest –TP49 used 360 stations for contiguous U.S day, 1964 Average Record Length over 50 Years –over double ≈ 1,500 Daily Stations in Southwest –TP49 used 360 stations for contiguous U.S day, 1964

New Statistical Approach Regional Analysis Based on L-Moments –Hosking & Wallis, 1997 L-Moments; More Robust Estimation –choosing distribution function –distribution shape –less sensitive to outliers Regional Approach –common distribution shape per region –but estimates are at site –pools information from many points –reduces uncertainty Uncertainty Estimates –possible with today’s computer power Regional Analysis Based on L-Moments –Hosking & Wallis, 1997 L-Moments; More Robust Estimation –choosing distribution function –distribution shape –less sensitive to outliers Regional Approach –common distribution shape per region –but estimates are at site –pools information from many points –reduces uncertainty Uncertainty Estimates –possible with today’s computer power

Area Reduction Factors Method From –NOAA Technical Report NWS 24, 1980 Last Real Update; TP29, 1957 –derived single curve for CONUS based on limited data –appeared in later documents (NA etc) –will test single curve hypothesis –update with either single or regional curves Geographically Centered –not storm centered For Areas square miles Method From –NOAA Technical Report NWS 24, 1980 Last Real Update; TP29, 1957 –derived single curve for CONUS based on limited data –appeared in later documents (NA etc) –will test single curve hypothesis –update with either single or regional curves Geographically Centered –not storm centered For Areas square miles

Temporal Distributions Approach from Huff –Illinois State Water Survey –“Huff Diagrams” modified for use with precip frequency Approach from Huff –Illinois State Water Survey –“Huff Diagrams” modified for use with precip frequency

Ensemble Modeling Statistical Analysis of Spaghetti Diagrams –based on different forcings Statistical Analysis of Spaghetti Diagrams –based on different forcings

Spatial Interpolation Statistical Estimates Are At Points –observation sites Accounting for High Resolution Spatial Variation –terrain, local climate –gridded interpolations 30 arc seconds PRISM Technology –Oregon State University Spatial Climate Analysis Service –hybrid statistical-geographic climate mapping –spatial grids of distribution means for each duration Cascade Residual Add-Back (CRAB) –smooth discontinuities from regional growth factor –incorporate regional and point estimates –use means only for SNOTEL –produce grids for each frequency Statistical Estimates Are At Points –observation sites Accounting for High Resolution Spatial Variation –terrain, local climate –gridded interpolations 30 arc seconds PRISM Technology –Oregon State University Spatial Climate Analysis Service –hybrid statistical-geographic climate mapping –spatial grids of distribution means for each duration Cascade Residual Add-Back (CRAB) –smooth discontinuities from regional growth factor –incorporate regional and point estimates –use means only for SNOTEL –produce grids for each frequency

Discussion