NOAA Atlas 14 Volume 11 Released Today – Better Rainfall Data for Texas
Engineers often begin projects with the following questions: when it rains, how much water infiltrates into the soil, how much water runs off, and how quickly does this water travel?
This exercise helps us to adequately size new infrastructure, develop safer building codes, and protect communities from flood hazards. Though there are many ways to evaluate the impacts of stormwater, the foundation of any of these methodologies is an understanding of rainfall depth, duration, and frequency – information which is primarily developed from studying historical gage data. Significant improvements have made it to Texas today, and there will be more to look forward to in the coming months.
How did we get here?
In 1935, a publication by D.L. Yarnell was released which described rainfall intensity-frequency data based on data from 200 first-order Weather Bureau stations. Five years after this publication, a hydrologic network of additional recording gages was installed – increasing the available short duration data by a factor of 20.
Starting in 1955, the Weather Bureau worked in cooperation with the Soil Conservative Service (SCS, now NRCS) to publish several technical papers on the development of rainfall intensity-duration-frequency relationships using the expanded gage data. Tying much of this work together, the Weather Bureau and the SCS then published Technical Paper 40 in 1961. TP-40 is still widely used and includes maps of the United States with data for different storms. This includes events with durations from 30 minutes to 1 day and return periods from 1 to 100 years. The user can flip to the map with the duration and return period of interest (e.g. a 2-year, 24-hour storm), locate their site on the map, and estimate a rainfall depth from the isopluvial lines. NOAA also published two documents to supplement TP-40 with additional durations: TP-49 in 1964 and NWS Hydro-35 in 1977.
For Texas, the US Geological Service (USGS) and Texas Department of Transportation (TxDOT) developed depth-duration frequency data which was published in 1998 (with additional updates in 2004). These studies incorporated nearly half a century of additional rainfall gage data.
Where are we now?
Among the best available data today are NOAA Atlas 14 Volumes 1 – 11, the first of which was released in 2006. These reports use more observation locations with a longer period of record and use more sophisticated statistical methods. Each volume focuses on a geographic region. Currently Washington, Oregon, Idaho, Montana, and Wyoming do not have a published volume that covers their region.
The Precipitation Frequency Data Server (PFDS) was developed alongside Atlas 14 to provide results and supporting information. The online tool allows the user to quickly and easily obtain data in many formats, including:
- Point estimates
- ArcInfo© ASCII grids and ESRI shapefiles
- Cartographic maps
- Associated Federal Geographic Data Committee-compliant metadata
- Annual maximum series and partial duration series data
The good news is that Volume 11 has been published with the support of many local sponsors. This volume covers Texas and approximately a 1-degree buffer area into adjacent states and Mexico. Almost 12,000 stations from 34 datasets were reviewed and 2,000 were retained for use in the frequency analysis. The supporting documentation is expected to become available online in mid-December of 2018.
The Hydrometeorological Design Studies Center (HDSC) within NOAA’s Office of Water Prediction (OWP) began work in 2016 with assistance from Penn State to assess nonstationary climate impacts on precipitation frequency estimates. These updates will be released in October 2018. The HDSC also began to collaborate with researchers at University of Illinois at Urbana-Champaign and University of Wisconsin-Madison in May 2018. This effort will continue to assess the feasibility of incorporating non-stationary climate impacts into the Atlas 14 rainfall frequency analysis.
The Atlas 14 rainfall data can be accessed here.
Though we’ve been studying rainfall for centuries, the amount of data available has increased drastically over just the past several decades. The computing and statistical tools we have at our fingertips has greatly expedited this progress and improvements to these technologies will only continue to help us better understand our environment. As cities become more densely populated, floodplain and stormwater managers face new challenges. With NOAA Atlas 14 becoming available to more of the US, the engineering, science, and planning communities have another tool in its toolbox to help make better decisions. Ultimately, these tools help us build safer and more resilient communities.
For more information or if you have questions, contact Hector Olmos, Garrett Johnston or Jeremy Dixon.
- United States Department of Commerce – Weather Bureau. Technical Paper No. 40. Rainfall Frequency Atlas of the United States. May 1961.
- United States Department of Commerce – Weather Bureau. Technical Paper No. 49. Two- to Ten-day Precipitation For Return Periods of 2 to 100 Years in the Contiguous United States. 1964.
- United States Department of Commerce – National Oceanic and Atmospheric Administration. Technical Memorandum NWS HYDRO-35. Five- to 60-minute Precipitation Frequency For the Eastern and Central United States. June 1977.
- United States Department of Commerce – National Oceanic and Atmospheric Administration. National Weather Service. NOAA Atlas 14. Precipitation-Frequency Atlas of the United States. Volumes 1- 10. 2006- 2015.