Data sources

The data behind every report

CurveNumber reads public datasets over the boundary an engineer draws and records where every figure came from. This page lists every dataset the product reads and the edition in use. Each report also has its own section on the data behind it, with the exact editions and the dates they were read, and that section is the record for that report.

These datasets are provided by their publishers without warranty. A dataset can be wrong at a particular site, and the report says where CurveNumber found reason to doubt one.

A dataset's retrieved date can be earlier than the day the areas were read. CurveNumber keeps a copy of each answer a publisher's service gives it, and a later request for the same map tile, soil survey area or storm point is answered from that copy rather than from the publisher again. The read date is when this site's areas were read; the retrieved date is when CurveNumber fetched that answer from the publisher, and the edition printed with it is the one that answer carries.

This list was last checked on Sep 24, 2026. Its address is https://curvenumber.com/data-sources.

Read over each site

Soil Survey Geographic Database (SSURGO), through Soil Data Access

Publisher: USDA Natural Resources Conservation Service
What CurveNumber takes from it: Soil map units and their published hydrologic soil groups.
Edition in use: The current version of each soil survey area on the day it is read. Each report prints the survey area and version it read, for example VA107 version 22 of Sep 4, 2025.
When it is read: Each time the public data is read for a site, from the publisher or from CurveNumber's copy of the same answer (see above).
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: websoilsurvey.nrcs.usda.gov/

Annual NLCD Land Cover and Fractional Impervious Surface (CONUS), Collection 1.0

Publisher: U.S. Geological Survey and the Multi-Resolution Land Characteristics Consortium
What CurveNumber takes from it: Land cover class and measured impervious share of each 30 m map square.
Edition in use: The latest year published, 2024 at present (the collection covers 1985 to 2024). Each report prints the year it read.
When it is read: Each time the public data is read for a site, from the publisher or from CurveNumber's copy of the same answer (see above).
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: www.mrlc.gov/data

NOAA Atlas 14, Precipitation-Frequency Atlas of the United States, Volumes 1 to 12

Publisher: NOAA National Weather Service, Hydrometeorological Design Studies Center, through the Precipitation Frequency Data Server
What CurveNumber takes from it: Design storm depths by duration and return period, and the published temporal distributions where a volume has them. Volume 12 covers Idaho, Montana and Wyoming (since Sep 2024).
Edition in use: The volume and version the server returns for the site. Each report prints the volume, version and retrieval date.
When it is read: When a site's storm is looked up, from the publisher or from CurveNumber's copy of the same answer (see above).
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: hdsc.nws.noaa.gov/pfds/

NOAA Atlas 2, Precipitation-Frequency Atlas of the Western United States (1973), Volumes IX and X

Publisher: NOAA National Weather Service
What CurveNumber takes from it: Design storm depths for Washington and Oregon, which NOAA Atlas 14 does not yet cover: 6-hour and 24-hour depths, 2 to 100 years, from NOAA's public-domain gridded copy.
Edition in use: 1973. Each report names it as NOAA Atlas 2 (1973).
When it is read: Stored with CurveNumber and sampled at the site.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: hdsc.nws.noaa.gov/pub/hdsc/data/westus/na2_westus_rast_metadata.html

3D Elevation Program (3DEP)

Publisher: U.S. Geological Survey, The National Map
What CurveNumber takes from it: Ground elevation and slope over the boundary, for the time of concentration.
Edition in use: The seamless elevation service as published on the day it is read.
When it is read: Each time the public data is read for a site, from the publisher or from CurveNumber's copy of the same answer (see above).
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: www.usgs.gov/3d-elevation-program

National Agriculture Imagery Program (NAIP) aerial photographs

Publisher: USDA Farm Production and Conservation Business Center, served by the U.S. Geological Survey
What CurveNumber takes from it: The aerial photograph of the boundary, when an engineer asks for it, classified into impervious, grass, trees and bare soil.
Edition in use: The most recent photograph published for the site. Each report prints the photograph's date.
When it is read: Live, only when the photograph is requested.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: naip-usdaonline.hub.arcgis.com/

Census Geocoder

Publisher: U.S. Census Bureau
What CurveNumber takes from it: Address search, and the county and state that contain the boundary, which the report checks against what was typed.
Edition in use: The current benchmark and current geography vintage on the day it is read.
When it is read: Live, when an address is searched or a site is located.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: geocoding.geo.census.gov/geocoder/

Read only for optional features

gridMET daily reference evapotranspiration

Publisher: University of Idaho, Northwest Knowledge Network
What CurveNumber takes from it: A first estimate of reference evapotranspiration for a green roof.
Edition in use: The dataset's own release attribute on the day it is read, printed on the estimate.
When it is read: Live, only when a green roof estimate is asked for.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: www.climatologylab.org/gridmet.html

Global Historical Climatology Network Daily (GHCN-Daily)

Publisher: NOAA National Centers for Environmental Information
What CurveNumber takes from it: Dry spell statistics from the nearest station, for a green roof estimate.
Edition in use: The station record through its last reported day, printed on the estimate.
When it is read: Live, only when a green roof estimate is asked for.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: www.ncei.noaa.gov/products/land-based-station/global-historical-climatology-network-daily

National Water Information System daily values

Publisher: U.S. Geological Survey
What CurveNumber takes from it: A stream gauge's daily record, when a curve number is fitted to a gauged record.
Edition in use: The record's approval status on the day it is read, printed on the calibration.
When it is read: Live, only when a calibration is run.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: waterdata.usgs.gov/nwis

Stored with CurveNumber

Technical Release 55, Urban Hydrology for Small Watersheds

Publisher: USDA Natural Resources Conservation Service
What CurveNumber takes from it: The curve number tables (Tables 2-2a to 2-2d), the runoff equation, the time of concentration method and the storm distributions Type I, IA, II and III.
Edition in use: Second edition, June 1986.
When it is read: Stored with CurveNumber.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: www.nrcs.usda.gov/resources/data-and-reports/urban-hydrology-for-small-watersheds-tr-55

National Engineering Handbook, Part 630 Hydrology

Publisher: USDA Natural Resources Conservation Service
What CurveNumber takes from it: The curve number method (Chapters 9 and 10) and the unit hydrographs (Chapter 16), including the Delmarva unit hydrograph used on the Delmarva coastal plain.
Edition in use: The chapters as currently published by NRCS; each report names the chapter it relies on.
When it is read: Stored with CurveNumber.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: directives.nrcs.usda.gov/

Gazetteer Files: places and ZIP Code Tabulation Areas

Publisher: U.S. Census Bureau
What CurveNumber takes from it: Place and ZIP code search on the map.
Edition in use: 2023.
When it is read: Stored with CurveNumber.
In use since: CurveNumber 0.9.0 (Sep 2026)
Where to read it: www.census.gov/geographies/reference-files/time-series/geo/gazetteer-files.html

National Transportation Atlas Database: Time Zones

Publisher: U.S. Department of Transportation, Bureau of Transportation Statistics
What CurveNumber takes from it: The site's local time zone, in which reports and published pages print their times. Arizona, the Navajo Nation and the Hopi Reservation are told apart with the Census Bureau's TIGERweb boundaries, because they differ on daylight saving time.
Edition in use: Time zone boundaries updated Jan 5, 2023; TIGERweb boundaries read Sep 24, 2026. Both simplified to about 300 m.
When it is read: Stored with CurveNumber.
In use since: Sep 24, 2026
Where to read it: geodata.bts.gov/datasets/usdot::time-zones/about