HR: 1340h
AN: GC13A-0950    [Abstracts]
TI: Abrupt changes in rainfall during the twentieth century
AU: * Narisma, G
EM: narisma@wisc.edu
AF: Center for Sustainability and the Global Environment Nelson Institute for Environmental Studies University of Wisconsin, Madison, 1710 University Ave., Madison, WI 53726, United States
AU: Foley, J
EM: jfoley@wisc.edu
AF: Center for Sustainability and the Global Environment Nelson Institute for Environmental Studies University of Wisconsin, Madison, 1710 University Ave., Madison, WI 53726, United States
AU: Licker, R
EM: rlicker@wisc.edu
AF: Center for Sustainability and the Global Environment Nelson Institute for Environmental Studies University of Wisconsin, Madison, 1710 University Ave., Madison, WI 53726, United States
AU: Ramankutty, N
EM: navin.ramankutty@mcgill.ca
AF: Department of Geography McGill University, 805 Sherbrooke St., Montreal, QC H3A 2K6, Canada
AB: A sudden change in climate is brought about by complex interactions in the climate system, including interactions between land and atmosphere, that can give rise to strong positive feedback mechanisms. Paleoclimatic studies have shown that abrupt climate changes have happened in the geologic past. Studies of future climate change under global warming scenarios indicate the possibility of the sudden collapse of the thermohaline circulation, which will have major implications for the climate of Europe. However, abrupt climatic changes are not events of the geologic past or a computer-simulated future: they have occurred in recent history and have had serious consequences on society and the environment. The prolonged Sahel drought in the late 1960s and the Dust Bowl of the 1930s are examples of abrupt climatic changes of the twentieth century. Apart from these events, however, there has been no systematic survey of recent climate history to determine the prevalence of abrupt climatic changes. Given the potential cost of these abrupt changes, there is a need to investigate historical records for evidence of other sudden climatic changes in the more recent past. Here we analyze the Climate Research Unit global historical rainfall observations (covering the years 1901-2000) using wavelet analysis to detect regions that have undergone large, sudden decreases in rainfall. We show that in the twentieth century, aside from the Sahel and the US midwest, at least 30 regions in the world have experienced sudden climatic changes. These events are statistically significant at the 99 percent level, are persistent for at least ten years, and most have magnitudes of change that are 10 percent lower than the climatological normal (1901-2000 rainfall average). We also illustrate some of the potential consequences of these abrupt changes and show that these events had major impacts on social and environmental conditions. Interestingly, these regions of abrupt precipitation changes are mostly located in semi-arid and arid regions (with rainfall amounts of about 350-700 mm per year). This is consistent with climate modeling results, which include the effects of dynamic vegetation cover. These studies show that arid and semi-arid regions are more likely to have multiple equilibrium states and exhibit abrupt "regime shifts" between states. Our analysis shows the extent and magnitude of sudden decreases in rainfall across the globe during the 20th century and is an important first step for studying dynamics of and the mechanisms behind these abrupt changes.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3354 Precipitation (1854)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting