RESEARCH AREAS

Extreme weather has large effects on human and natural systems. Through the use of observations, climate model and statistical techniques, CASCADE researchers examine how changes in the natural environment have impacted recent weather extremes.

Increased understanding of the influence of environmental drivers on current extreme weather increases confidence in projections of changes in future extreme weather statistics.  The centerpiece modeling effort of the CASCADE Detection and Designation team is the C20C+ (Climate of the 20^th Century) experiment. CASCADE is a primary contributor to the World Climate Research Program (WCRP) coordinated international project. This multi-model effort aims to aid event attribution by building a database of ensemble climate model simulations describing the “world that was” in a realistic-as-possible configuration and the “worlds that might have been” in a counterfactual configuration where environmental drivers have not changed.

Associating changes in the behavior of extreme events to specific environmental drivers requires a systematic characterization of extreme events in the recent past. Recent advances in simulation capabilities and statistical methodologies allow us to focus on the impacts of a wide range of environmental drivers at regional-to-local scales, to focus on factors impacting the spatial and temporal co-occurrence of extremes, and to simulate how we might expect extremes to change in the future.

Climate extremes – such as hurricanes, major floods, and heat waves – not only stress society, they push the bounds of what modern climate models can simulate.

While extreme weather events often have impacts at relatively small (city-wide) scales, they are often driven by planetary scale forces. Observing and simulating these events requires datasets and models with high fidelity at a wide range of scales.  CASCADE is making novel use of self-similarity* in the atmosphere to define new standards for how model performance should change as model scale changes from ‘city’ to ‘planetary’. The CASCADE team is using the Department of Energy’s new Accelerated Climate Model for Energy (ACME) to simulate past weather and is using these new standards to evaluate the model.  Through a tight collaboration with ACME developers, these insights are being translated in to improved model fidelity at a wide range of scales.

Designating and projecting changes in extremes requires a well-developed understanding of the processes that drive changes in extremes. In particular, for the overall goal of the CASCADE SFA, it is necessary to understand how have changes in the physical behavior of the coupled system altered the frequencies of occurrence and the characteristics of extreme climate events? To address this issue, it is also necessary to advance our understanding of the processes governing the properties of extremes that are being investigated within the CASCADE SFA. The SFA team focuses specifically on the processes that drive multivariate extremes, the processes that drive changes in the spatio-temporal characteristics of extremes, and the fidelity with which these processes are represented in climate models.

*self-similarity means that the statistics of the atmosphere change predictably depending on the scale at which the statistics are evaluated