Atlas 14 IDF Calculator
Rainfall depth and intensity for any Texas location from NOAA Atlas 14 — the full table, IDF curves, and a value for any duration.
Results
Enter your values; the answer appears here as you type.
The curve appears with a result.
- NOAA Atlas 14 Volume 11
- Precipitation frequency estimates for Texas (Version 2.0, 2018) on a 30-arc-second grid (about 0.8 km): 15 durations from 5 minutes to 10 days and 10 average recurrence intervals from 1 to 1,000 years. Both NOAA series are available: the partial-duration series (PDS) means that NOAA’s Precipitation Frequency Data Server (PFDS) shows by default, and the annual maximum series (AMS, 2- to 1,000-year). Which series a project uses is set by the reviewing agency’s criteria.
- Same numbers as the Rainfall Map
- The calculator reads the tiles of the Texas Atlas 14 Rainfall Map, built from NOAA’s published grids and checked against NOAA PFDS text output. Only the 0.5-degree tile around your location loads (about 140 KB).
- Intensity
- Average intensity is the depth divided by the duration (in/hr). Intensity-duration-frequency (IDF) curves plot it against duration on a log scale.
- Durations between the published ones
- For a duration between two published durations (for example a 25-minute time of concentration) the depth is interpolated on a straight line of log depth against log duration. Grid values are never changed, and return periods are not interpolated.
- Location
- Type coordinates, or an address: the address is sent to the U.S. Census geocoder and only Texas matches are offered. Coordinates and results stay in your browser.
The calculator is tested against the cases below every time its code changes.
| Case | What | Reference | Values compared | Largest difference | Result |
|---|---|---|---|---|---|
| The table loads with the calculator. The same results are in verification.json. | |||||
Every case compares all 150 grid values at one location with NOAA PFDS text output for the same coordinates; a case passes only when every displayed value matches exactly. The intensity and interpolation cases are arithmetic checks.
- Point values only: no areal reduction for large watersheds, no temporal distributions and no storm hyetographs.
- Mean estimates only: the 90% confidence bounds are on NOAA PFDS. The annual maximum series has no 1-year value.
- Texas only (NOAA Atlas 14 Volume 11). NOAA Atlas 15 preliminary values are not used.
- What is the difference between depth and intensity?
- Depth is the total rain that falls in the duration (inches); intensity is the average rate over that duration (inches per hour). The Rational Method uses intensity for a duration equal to the time of concentration.
- What does a 100-year rainfall mean?
- A depth that is equaled or exceeded on average once in 100 years at that location (an average recurrence interval). For long intervals the chance in any one year is about 1 in the interval: about 1% for 100 years. It can occur in consecutive years.
- Why does my value differ slightly from an older table?
- Atlas 14 Volume 11 (2018) replaced TP-40 and USGS-era values in Texas, and many local criteria manuals updated their tables after it. Older tables, county averages and interpolated maps can differ by several percent or more.
- Can I attach the calculation sheet to a design report?
- You can print it and include it as a supporting calculation that you have checked. It is a calculation aid, not a sealed engineering document: the engineer of record reviews it and is responsible for the design, and the criteria of the reviewing agency decide which methods and values apply.
| Topic | Reference |
|---|---|
| Precipitation frequency | Perica, S., et al. (2018). NOAA Atlas 14, Precipitation-Frequency Atlas of the United States, Volume 11 Version 2.0: Texas. NOAA, National Weather Service. |
| Data server | NOAA Hydrometeorological Design Studies Center, Precipitation Frequency Data Server (PFDS). |
| Same data on a map | Texas Atlas 14 Rainfall Map (HERO E&C). |
Need an engineer’s review of this calculation?
HERO E&C prepares drainage and floodplain studies, channel and culvert design, HEC-HMS / HEC-RAS models, and development permit applications across Texas.
A free calculation aid using the published methods above. Not a sealed engineering document; the engineer of record is responsible for design. HERO E&C · TBPELS Firm F-27793.
Full disclaimer
A free calculation aid. This calculator applies the published methods named on this page to the inputs you enter. It is not a sealed engineering document, has not been reviewed by a licensed professional for your project, and no warranty is expressed or implied. Check the results independently before using them for design, bidding or permitting.
The criteria of the reviewing agency decide which methods and values apply to a design. The engineer of record is responsible for the design.
Using this calculator does not create an engineer–client relationship. Calculations run in your browser; your inputs are not sent to or stored by HERO E&C. HERO E&C · TBPELS Firm F-27793.