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The Effect of Projected Sea Surface Temperature (SST) Pattern Changes on Tropical Precipitation using CESM 1
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  • Amanda Bowden,
  • Eric Maloney,
  • Justin Hudson,
  • Michael Natoli,
  • Justin Whitaker
Amanda Bowden
Colorado State University

Corresponding Author:[email protected]

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Eric Maloney
Colorado State University
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Justin Hudson
Colorado State University
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Michael Natoli
Colorado State University
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Justin Whitaker
Colorado State University
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Abstract

Tropical islands are highly dependent on rainfall to provide resources for drinking and agriculture. Hence, understanding changes to precipitation under a changing climate is critical for societal planning. Decadal variability in the climate system causes the strength of SST gradients to vary across the tropical Pacific that can cause precipitation patterns to transition from one decade to the next, even in the presence of longer term climate trends. To study 21st Century changes to tropical rainfall patterns in the presence of decadal variability, we use the CESM1 Large Ensemble (Kay et al. 2015) forced under RCP8.5. Each ensemble member uses different initial conditions that can be used to examine climate projections on short term (e.g. weeks, years) through long term (e.g. century) time scales. Since climate models contain climate variability such as El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), each ensemble member can have diverse projection outcomes in a given decade. While all ensemble members eventually show an El Niño-like warming pattern by 2100 relative to 1985-2005, before the mid 21st Century, preferential SST warming and precipitation intensity in the tropics in any given 20-year period can be weighted toward the west, central, or east Pacific. Further, while Niño3.4 SST generally goes up relative to 1985-2005, the tropical Pacific east-west temperature gradient change does not show as consistent an upward trend. Implications of SST and precipitation change patterns for Guam, Samoa, Hawaii, and Puerto Rico are examined. Spearman’s correlation is used to examine the relationship between station island precipitation and the east-west Pacific SSTs gradient change. A strong negative correlation relative to gradient change is found for Guam, in contrast to Samoa having a high positive correlation. This study highlights the importance of decadal climate variability for understanding changes in water resources in island nations in a changing climate. This study was conducted as part of the Earth System Modeling and Education Institute summer REU program at Colorado State University.