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Publication Date
1 September 2021

Rise in Northeast US Extreme Precipitation Caused by Atlantic Variability and Climate Change

Subtitle
The abrupt increase in Northeast US extreme precipitation after 1996 is caused by the Atlantic variability and anthropogenic climate change.
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Extreme precipitation anomalies over the Northeastern US in the GHCN-D observations (OBS), CESM1 historical all-forcings (ALL) and single forcing simulations (GHG: greenhouse gases, AER: aerosols, BMB: biomass burning, and LULC: land use and land cover).
Science

Extreme precipitation (EP) in the Northeastern United States increased abruptly after 1996. Here EP is defined as precipitation falling in the heaviest 1% of wet days. This increase coincided with warming Atlantic sea surface temperatures (SSTs). Yet the causes underlying the 1996 Northeast EP shift remain unclear.

Impact

Understanding the causes of the EP increase since 1996 is crucial to correctly interpret future simulations of EP. It can also help inform the range of EP impacts the Northeast needs to be prepared for. This study shows that external forcings have significantly influenced both Northeast EP and North Atlantic SSTs. Greenhouse gases are the primary anthropogenic forcing exerting influence on EP. Furthermore, unforced Atlantic variability, along with external forcings, may contribute to Northeast EP through increasing North Atlantic SSTs and therefore tropical cyclone EP events over the Northeast.

Summary

To understand the causes of the Northeast EP and North Atlantic SST changes over 1929–2018, we used the Community Earth System Model version 1 (CESM1) large ensemble simulations and a statistical method named optimal fingerprinting. This approach allows us to separate and quantify the roles of internal variability and external forcings (including anthropogenic and natural forcings) on the observed changes of North Atlantic SSTs and Northeast EP. We find that external forcings have significantly influenced both Northeast EP and North Atlantic SSTs. Greenhouse gases are the only anthropogenic forcing exerting substantial influence on EP, first detected in 2008. The warming of North Atlantic SSTs since the 1990s is attributable to internal variability of the Atlantic, anthropogenic aerosols, and greenhouse gases. They altogether may lead to the anomalously high EP through inducing more tropical cyclone EP events over the Northeast. We, therefore, attribute the 1996 EP shift to both unforced Atlantic variability and anthropogenic forcings.

Point of Contact
Huanping Huang
Institution(s)
Lawrence Berkeley National Laboratory
Funding Program Area(s)
Publication