Céline Bonfils : Then and Now / 2012 Early Career Award Winner

Despite the devastating impacts of drought on human and natural systems, long-term changes in droughts remain poorly understood. Can we explain why arid conditions are spreading worldwide? Or why the western United States is getting increasingly arid since the 1980s while the Sahel has recovered from its prolonged drought? Are these events independent or connected by large-scale mechanisms?

While the scientific community has engaged in many attempts to investigate the physical mechanisms of droughts, understanding their underlying causes in the context of climate change has become critical.

Receiving the DOE Early Career Award was a great honor. The award gave me an inestimable opportunity to carve my own research path and explore these questions along with world-renowned experts.

The challenge of identifying a human signal in climate observations is typically addressed using detection and attribution techniques. However, these techniques had seen little application in drought research.

My goal was to refine and adapt the “pattern-based” fingerprinting approach to the hydroclimate system. Implemented by Benjamin Santer, this approach was conceptualized by Klaus Hasselmann. Hasselmann’s work received the 2021 Nobel Prize in Physics for theorizing a statistical framework able to identify a human-caused warming signal.

Like musical instruments contribute to a symphony, the climate results from multiple influences acting together. These contributors include internal noise of Earth’s climate, such as the purely natural fluctuations like El Niños and La Niñas, and external forcing agents, such as occasional volcanic eruptions, atmospheric pollution, and the accumulation of heat-trapping greenhouse gases.

Each contributor imprints the Earth’s climate with unique temporal and geographical patterns. My collaborators and I identified these “fingerprints” in historical climate simulations to help separate the signals from the noise in observations.

Thanks to this award, we have successfully transitioned from identifying the influence of human activities on esoteric aspects of climate change (tropopause height, stratospheric temperature) to aspects of greater societal relevance (rainfall, aridity, water vapor, cloudiness, snowpack, streamflow).

Céline Bonfils is a physicist at Lawrence Livermore National Laboratory.

The Early Career Research Program provides financial support that is foundational to early career investigators, enabling them to define and direct independent research in areas important to DOE missions. The development of outstanding scientists and research leaders is of paramount importance to the Department of Energy Office of Science. By investing in the next generation of researchers, the Office of Science champions lifelong careers in discovery science.

For more information, please go to the Early Career Research Program.

Title – Detection and Attribution of Regional Climate Change with a Focus on the Precursors of Droughts

Abstract
The goal of this project is to improve understanding of the nature and causes of past changes in droughts to identify potential onset of future drought. The problem of identifying a component forced by climate change is typically addressed using established statistical detection and attribution (D&A) techniques. These techniques identify the characteristic “fingerprints” associated with climate change and connect them to likely causes in the system. However, these techniques have seen little application in drought research because of the noisy nature of the observations in this field.

This project, instead of solely focusing on changes in drought characteristics, will investigate the naturally driven and externally forced components of known large‐scale drought precursors such as specific ocean temperature patterns or poleward shifts in atmospheric circulation.

The research will include an analysis of drought behavior in various climate model simulations and observations; a D&A‐derived technique to investigate the temporal changes in major oceanic precursors; an uncertainty quantification analysis based on the 1998‐2003 drought; and a rigorous D&A analysis of drought‐promoting changes in atmospheric circulation patterns.

This research will improve the understanding of drought mechanisms, establish new avenues in regional D&A research, and examine the sensitivity of the results to specific sources of uncertainties in the climate models, in measurements, in the climate drivers, and in the D&A methods.

Ultimately, this work will provide scientific underpinning to inform decisions on how society might adapt to droughts in a changing climate

C Bonfils, BD Santer, J Fyfe, K Marvel, T Phillips, and S Zimmerman, “Human influence on joint changes in temperature, rainfall, and continental aridity.” Nature Climate Change 10, 726 (2020). [DOI:10.1038/s41558-020-0821-1].

C Bonfils , BD Santer, TJ Phillips, K Marvel, R Leung, C Doutriaux and A Copotondi, “Relative contributions of mean-state shifts and ENSO-driven variability to precipitation changes in a warming climate.” Journal of Climate 28, 9997 (2015). [DOI:10.1175/JCLI-D-15-0341.1]

K Marvel and C Bonfils, “Identifying external influences on global precipitation.” Proceedings of the National Academy of Sciences 110, 19301 (2013). [DOI:10.1073/pnas.1314382110]

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Additional profiles of the Early Career Research Program award recipients can be found at /science/listings/early-career-program. 

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