Capturing Extremes: The CASCADE SFA

Source:  Bill Collins and Dan Hawkes

CASCADE is investigating whether and how current hurricanes are affected by global climate change and how these effects will be amplified by future climate change. At the top is a satellite image of Superstorm Sandy while at the bottom is a simulation of a typical Atlantic hurricane.

Changes in the risk of extreme weather events may pose some of the greatest hazards to our society and environment, as the climate changes due to anthropogenic (i.e., human-caused) warming. Extreme weather has recently focused public attention on the dramatic consequences that follow from such events. In 2011, unusually high precipitation, combined with high snowpack, caused extensive flooding throughout the central United States. In 2012, a heat wave across the same region produced the country’s hottest year on record, and Superstorm Sandy caused severe storm surges along the Eastern seaboard. The year 2013 brought intense downpours and subsequent flooding across Colorado’s front range, causing equally unprecedented damage.

Clearly, we need to get a handle on these extreme events--to predict such events with greater reliability, to predict how such extreme events might change in the future, and to determine whether the nature of extreme events has already changed, and why.

Last month (October 2013) in response to this challenge, DOE initiated the development of a comprehensive climate model that would simulate extreme events, as part of the Calibrated and Systematic Characterization, Attribution and Detection of Extremes (CASCADE) Scientific Focus Area (SFA)—to advance scientific capabilities in studying climate extremes and in conducting extreme climate analysis. The CASCADE SFA, awarded by DOE’s Regional and Global Climate Modeling Program, will be a three-year ($2.25 M per year) multi-organizational project centered at LBNL, with ESD Climate Sciences Department Head Bill Collins serving as principal investigator. ESD climate scientists Travis O'Brien, Soyoung Jeon, and Karthik Kashinath will also be working on this project.

The program has a number of different aims. It will (1) advance understanding of the connections among scales, intensities, causative factors, and impacts of extremes; (2) develop new frameworks by which to identify the fidelity of simulated extremes using multimodel hindcasts, near-term forecasts, and perturbed-physics ensembles; and (3) apply this information to determine uncertainties in simulated future trends in extremes from the Community Earth System Model (CESM) system.  Finally, the CASCADE team will advise developers on how best to improve the fidelity of climate extremes simulated by DOE’s state-of-the-science climate models.

One key aspect of the team's approach to meeting its aims will be to develop and apply new methods for extreme event detection and characterization. These methods will utilize advanced statistical techniques and uncertainty quantification and analysis, realized as software capable of processing extreme amounts of simulation and observational data on the world's largest computational platforms. This software will be architected and deployed in a way to leverage community support and to be extendable and usable by the broader climate community.

This work is anticipated to produce several significant new capabilities for climate science. These capabilities include development of high-throughput pipelines to determine various uncertainties in model simulation, creation of flexible and extendable linkages among widely used statistical and analytic tools for end-to-end workflows, and extension of uncertainty quantification tools to treat a wide variety of extreme phenomena.

The CASCADE SFA will draw upon the expertise of a diverse team of climate scientists, computational scientists, and statisticians—from LBNL’s Computational Research Division as well as from ESD--along with scientists from U.C. Berkeley and U.C. Davis. The work will be coordinated with other related projects already under way at LBNL, including large-scale simulations of climate extremes in the recent past and near-term future, and the wide-ranging, collaborative investigation of multiscale processes in the climate system. The resulting connections and related projects will ensure tight integration of observations, experiments, and modeling of extreme climate phenomena.

Collins and other members of the project's leadership have contributed to a number of international climate assessment reports—including the last two Intergovernmental Panel on Climate Change reports--that have shaped the public dialogue about climate change. Members of the CASCADE team have also developed new statistical methods for understanding extreme weather phenomena, have published high-performance software tools for climate data analysis, and have led the development of the next generation of Earth system models.