CONUS NG-IDF Data Sets

The NG-IDF datasets, spanning 1951‒2013, characterize the magnitude, trend, seasonality, and driving mechanism of extreme events relevant to hydrologic design for over 200,000 locations across the CONUS at a 1/16th-degree resolution. These datasets enhance traditional precipitation-based intensity-duration-frequency curves (PREC-IDF) by accounting for total water reaching the land surface from rainfall, snowmelt, and rain-on-snow (ROS), i.e., Next-Generation intensity-duration-frequency analysis (NG-IDF).

PREC-IDF's neglect of snow processes can lead to significant biases in extreme event analysis, especially in snowy regions. NG-IDF addresses this by including snow processes, providing a systematic and consistent technique for all environments from rain-dominated, transitional, to snow-dominated locations. The resulting datasets are spatially continuous, and readily usable for supporting site-specific infrastructure design and for assessing the potential biases and design risks related to the use of PREC-IDF.

Abbreviations:

P = Precipitation

R = Rainfall

ROS = Rain-on-snow

M = Snowmelt 

W = Water reaching the land surface from rain, snowmelt, and ROS events

Classification of Driving Mechanism for Extreme W Events:

For each location, the driving mechanism was determined for extreme W events with different durations and return periods, following the classification criteria as follows:

Rainfall (R): precipitation on snow-free ground; 

Snowmelt (M): decreasing SWE, daily rainfall < 10 mm, and the sum of rainfall and snowmelt has < 20% contribution from rainfall.

Rain-on-snow (ROS): decreasing SWE with at least 10 mm of daily rainfall falling on a snowpack with at least 10 mm daily SWE, and snowmelt contributes at least 20% of the total of rain and snowmelt

The datasets include:

Note: In data format description, C = column, R = row, C[i] indicates the ith column of a data file. All data files are prepared in comma-separated value (.csv) format.

• list.csv
  • Description: The geographic coordinates and cluster ID (used for snow parameterization) of 207,173 locations over the CONUS
  • Data Dimension: 207,173 (R) x 3 (C)
  • Format: C1: Latitude; C2: Longitude; C3: cluster ID (ranging from 1‒5)

• AMF_WY/
  • Description: Annual maximum series with durations of 24h, 48h, and 72h, driven by different hydrometeorological mechanisms over water years 1951‒2013 (10/1/1950-09/30/2013). The mechanisms include W, P, R, ROS, and M.
  • Subfolder/File Naming Convention: [duration]/[mechanism].csv, e.g., 24h/W.csv
  • Data Dimension: 207,173 (R) x 65 (C)
  • Unit: mm
  • Format: C1: Latitude; C2: Longitude; C3‒C65: maximum value for each year from 1951-2013

• AMF_CY/
  • Description: Annual maximum series with durations of 24h, 48h, and 72h, driven by different hydrometeorological mechanisms over calendar years 1950‒2012 (1/1/1950-12/30/2012). The mechanisms include W, P, R, ROS, and M.
  • Subfolder/File Naming Convention: [duration]/[mechanism].csv, e.g., 24h/W.csv
  • Data Dimension: 207,173 (R) x 65 (C)
  • Unit: mm
  • Format: C1: Latitude; C2: Longitude; C3‒C65: maximum value for each year from 1950-2012

• IDF/
  • Description: Discrete IDF values, i.e., the magnitude of extreme events with durations of 24h, 48h, and 72h, driven by different hydrometeorological mechanisms. The mechanisms include W, P, R, ROS, and M.
  • Subfolder/File Naming Convention: [duration]/[mechanism].csv, e.g., 24h/W.csv
  • Data Dimension: 207,173 (R) x 9 (C)
  • Unit: mm
  • Format: C1: Latitude; C2: Longitude; C3‒C9: IDF values for the return period of 2, 5, 10, 25, 50, 100, and 500 years. NaN indicates no runoff caused by a given mechanism, such as ROS.

• IDF_90CI/
  • Description: 90% C.I. for IDF values in the IDF/ folder described above
  • Subfolder/File Naming Convention: [duration]/[mechanism]_H.csv, e.g., 24h/W_H.csv
    • Data Dimension: 207,173 (R) x 9 (C)
    • Unit: mm
    • Format: C1: Latitude; C2: Longitude; C3‒C9: 95% quantile for IDF values with the return period of 2, 5, 10, 25, 50, 100, and 500 years. NaN indicates no runoff event caused by a given mechanism.
  • Subfolder/File Naming Convention: [duration]/[mechanism]_L.csv, e.g., 24h/W_L.csv
    • Data Dimension: 207,173 (R) x 9 (C)
    • Unit: mm
    • Format: C1: Latitude; C2: Longitude; C3‒C9: 5% quantile for IDF values with the return period of 2, 5, 10, 25, 50, 100, and 500 years. NaN indicates no runoff event caused by a given mechanism.

• trend/
  • Description: Sen's slope of Mann-Kendall trend in annual maximum series driven by different hydrometeorological mechanisms over water years 1951‒2013. The mechanisms include W, P, rainfall (R), ROS, and snowmelt (M).
  • Subfolder/File Naming Convention: [duration]/[mechanism].csv, e.g., 24h/W.csv
  • Data Dimension: 207,173 (R) x 3 (C)
  • Unit: mm/year
  • Format: C1: Latitude; C2: Longitude; C3: Trend indicated by Sen's slope. The value is zero if the trend is not statistically significant.

• Driver/
  • Description: Dominant driving mechanism of extreme W events with different durations and return periods
  • Subfolder/File Naming Convention: [duration]/[return period].csv, e.g., 24h/50y.csv
  • Data Dimension: 207,173 (R) x 3 (C)
  • Format: C1: Latitude; C2: Longitude; C3: Dominant driver IDs (1=R, 2=ROS, 3=M).

• risk/
  • Description: Design risk associated with PREC-IDF estimated 100-year extreme events
  • Subfolder/File Naming Convention: [duration]/100y.csv, e.g., 24h/100y.csv
  • Data Dimension: 207,173 (R) x 3 (C)
  • Unit: %
  • Format: C1: Latitude; C2: Longitude; C3: Bias in the 100-year event based on PREC-IDF vs. NG-IDF

• SI/
  • Description: Seasonality of annual maximum W events with 24-, 48-, and 72-h durations over water years 1951‒2013
  • Subfolder/File Naming Convention: [duration]/W.csv, e.g., 24h/W.csv
  • Data Dimension: 207,173 (R) x 4 (C)
  • Format: C1: Latitude; C2: Longitude; C3: Mean data (=1 if Oct 1); C4: Seasonality index ranging from 0 to 1