Projections of Extreme Precipitation Amounts for Climate Adaptation Planning in New York State

A set of future extreme precipitation probabilities are developed for New York State based on different downscaling approaches and climate model projections. Based on nearly 50 downscaling method-climate model combinations, percent differences are computed between simulated extreme precipitation amounts for one historical (1970-1999) and three future (2010-2039, 2040-2069, and 2070-2099) time periods. These percent change factors are then applied to the observed extremes to estimate future precipitation extremes. The results are presented to users via an interactive website (http://ny-idf-projections.nrcc.cornell.edu). As the engineering community is the primary user, the website displays intensity-duration-frequency (IDF) graphs depicting the: 1) mean projected extreme precipitation intensity, 2) range of future model projections, 3) distribution of observed extreme precipitation intensities, 4) confidence intervals about the observed values.

One-hundred-year recurrence interval precipitation amounts exhibit a median increase of between 5 and 10% across the state in the 2010-2039 period regardless of greenhouse gas concentration. By the 2040-2069 period, the median increase is on the order of 10-20% for the high concentration case (RCP 8.5), but remains below 10% if concentrations are lower (RCP 4.5) At the end of the century, all downscaling method climate model combinations indicate increases, with a median change of between 20-30% in the case of high concentrations.