The Extreme Weather and Climate Change program at Davis focues on extreme weather events, including tropical and extratropical cyclones, heat waves, droughts, atmospheric blocks and other features which have the potential for large socioeconomic damage. The IPCC special report on extreme weather reports with confidence that the next century will see substantial warming, with a corresponding increase in regional temperature extremes and drought conditions, increases in the frequency of heavy precipitation events in wet areas, and increases in tropical cyclone wind speeds. Forcing from anthropogenic sources, including carbon dioxide emissions, have already been responsible for a roughly 1 degree increase in global temperatures since the pre-industrial era. However, the question of the influence of human activity on the frequency and magnitude of extreme weather events of the past decade has remained largely unanswered. Students in extreme weather are working to better understand extreme weather and how extremes will be changing over the next century.
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Professor Grotjahn has a number of research projects in extreme weather and climate change. He works on the synoptic to global length scales. Examples of past projects include the following. (1) Fluid dynamical instability of midlatitude flows using such tools as: large linear eigenvalue problems, linear initial value problems, and nonlinear initial value problems in Cartesian and spherical geometry. Our approach is to ground our theoretical studies with targeted observational studies and vice-versa. (2) Forecasting work includes model verification and constructing historical analogs from past extraordinary weather events. (See the forecast analogs website for significant large-scale patterns associated with such regional events as: severe freezes, heat waves, and heavy rain.) These studies employ various statistical analysis tools. Current research includes the following projects: (3) studies of what factors, both local and remote, maintain the subtropical highs, (4) research following up on Dr. Grotjahn’s book on the general circulation, (5) studies of what model defects are causing specific Arctic region surface climate biases in climate models, (6) study of the origin of air reaching California (relevant to air quality compliance), and (7) application of analog techniques to identify the climatology of extraordinary weather in a climate undergoing global change.
The effect of climate change on extreme ozone and PM2.5 concentrations is a major concern for California. Professor Kleeman's research down-scales decades of climate to examine how extreme air pollution events may change in the future. His research couples the course-scale outputs from GCMs at 100's of km to regional models that can predict results at 4km or even 250m resolution. This work includes development of future emissions inventories along different energy pathways to fully characterize the range of possible scenarios for future air pollution in California.
Professor Nathan's research is fundamental in nature and focuses on identifying and understanding the physical and dynamical mechanisms that govern the spatial and temporal evolution of large-scale atmospheric circulation systems. Professor Nathan's research involves combining observations with advanced mathematical techniques to study the following: tropical-midlatitude interactions during El Niño and La Niña flow regimes; stability of geophysical fluid flows; nonlinear dynamics of atmospheric circulations; and interactions among radiation, ozone and dynamics in the stratosphere. Additional research includes using proxy data (e.g. dendroclimatic reconstruction and historical records) to examine the impacts of meteorological events on exploration, including the Lewis and Clark expedition.
Professor Ullrich's research in extreme weather focuses on understanding changes in synoptic scale weather systems in response to future climate change. The next century will see unprecedented changes to the climate system which will have significant repercussions on global human activity and international policy. The IPCC special report on extreme weather reports with confidence that the next century will see substantial warming, with a corresponding increase in regional temperature extremes and drought conditions, increases in the frequency of heavy precipitation events in wet areas, and increases in tropical cyclone wind speeds. These trends are of a broad global nature and do not necessarily reflect the influence of the changing global climate on regional scales, which are absolutely key for planning on the local, state and federal level. For this reason, an understanding of changing regional climate and synoptic-scale weather is an unmet challenge that must be addressed in the coming decade.
Bryan Weare (Emeritus)
Professor Weare studies atmospheric processes associated with such varied tropical short-term climate variations as El Niño events, the 40-50 day wind oscillation and the possible impact of global climate change. This research is aimed at understanding how climate is affected by diabatic heating at the bottom, top and within the atmosphere through the use of both models and observations. The data include ship derived observations from which the heat budget at the ocean surface may be derived, together with satellite estimates of the radiation budget at the top of the atmosphere. The goal of Professor Weare is to use sophisticated statistical analysis techniques to diagnose how the pattern of climate changes relates to the basic forcing terms in both models and the real atmosphere. A major component of his research is to understand how cloudiness in the tropics interacts with El Niño and climate change. Professor Weare applies modern statistical techniques such as autoregressive spectra, regular and complex empirical orthogonal functions and linear and nonlinear multiple regressions in his research work. Other areas of interest of Professor Weare include improving statistical techniques for analysis and prediction and estimating the impacts of potential changes in climate on agriculture.