RaInDROP Tool

Extreme precipitation events can sometimes occur with greater intensity, frequency, or duration, leading to conditions that favor more widespread or severe flooding. Warmer temperatures can also increase evaporation rates, resulting in more atmospheric moisture and the potential for heavier precipitation.

The current practice within the United States is to use NOAA Atlas 14 Intensity-Duration-Frequency (IDF) precipitation values for set durations (e.g., 24-hour) and return periods (e.g., 50-year storm). Since the release of the next version, Atlas 15, is still several years away, the State Climate Office of North Carolina developed a dataset that illustrates how precipitation patterns represented in Atlas 14 may evolve over time.  

This effort adjusted NOAA Atlas 14 values across North Carolina using scale factors derived from a statistical downscaled dataset. The analysis examined plausible changes for two periods (mid-century and end-of-century) and two modeled future conditions (moderate and high scenarios). IDF curves were then created to help quantify changes in regional precipitation extremes.  The adjustment factors were derived using the Localized Constructed Analogs (LOCA) statistical downscaling method, which has approximately a 6-km horizontal resolution. LOCA datasets were previously used in national hydrologic assessments.

These adjustment factors were applied to NOAA Atlas 14 data at individual grid points across North Carolina to develop a tool that provides point-based frequency estimates – the Future IDF Curve Tool. This Rainfall, Intensity, Duration and Return for Observations and Projections (RaInDROP) Tool lets users conveniently explore updated precipitation frequency information. Precipitation intensity is calculated by dividing precipitation depth (inches) by duration (hours).

The tool is still in beta form/development.