Assessing Future Climate Extremes over the United States Using the rCEI Index

Anthropogenic climate change is a complex global issue, with repercussions for virtually every facet of human life, from public health to economics to ecology. Much of our current risk assessment, especially for extreme events and natural disasters, comes from the assumption that the likelihood of future extreme events can be predicted based on the past. However, as global temperatures rise, established ranges may no longer be applicable, as historic records for extremes such as heat waves and floods may no longer accurately predict the changing future climate. To assess extremes (present-day and future) over the contiguous United States, I used NOAA’s regional Climate Extremes Index (rCEI), which evaluates extremes in maximum and minimum temperature, extreme one-day precipitation, days without precipitation, and the Palmer Drought Severity Index (PDSI). The rCEI is a spatially sensitive index which uses percentile-based thresholds rather than absolute values to determine climate extremeness, and is thus well-suited to regional comparison. I used regional climate model data from NARCCAP and CORDEX to compare a late 20th century reference period to a mid-21st century extreme (RCP8.5 and SRES A2) scenario. Additionally, I used CMIP3 and CMIP5 data to compare regional climate model data to its global climate model boundary forcings, to see what added value the regional climate models provide in the Mid-Atlantic region. Preliminary results show a universal increase in extreme temperatures across all models, with annual average maximum temperatures exceeding historic 90th percentile thresholds over more than 90% of the area assessed by 2068. Results for precipitation indicators have greater spatial variability from model to model, but indicate an overall trend of less frequent but more extreme precipitation days.