Warming and earlier spring increase western U.S. forest wildfire activity.

Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th- and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.

A 5000-year record of extreme floods and climate change in the southwestern United States.

A 5000-year regional paleoflood chronology, based on flood deposits from 19 rivers in Arizona and Utah, reveals that the largest floods in the region cluster into distinct time intervals that coincide with periods of cool, moist climate and frequent El Niño events. The floods were most numerous from 4800 to 3600 years before present (B.P.), around 1000 years B.P., and after 500 years B.P., but decreased markedly from 3600 to 2200 and 800 to 600 years B.P. Analogous modern floods are associated with a specific set of anomalous atmospheric circulation conditions that were probably more prevalent during past flood epochs.

Climate and Chlorophyll a: Long-Term Trends in the Central North Pacific Ocean.

Since 1968 a significant increase in total chlorophyll a in the water column during the summer in the central North Pacific Ocean has been observed. A concomitant increase in winter winds and a decrease in sea surface temperature suggest that long-period fluctuations in atmospheric characteristics have changed the carrying capacity of the central Pacific epipelagic ecosystem.

Large-scale air-sea interactions and short-period climatic fluctuatioins.

Research during the last 15 years has shown that there is order in large-scale air-sea interactions, so that space scales of abnormalities of the lower atmosphere's circulation and the upper oceanic thermal structure are comparable. Because of this air-sea coupling, each oceanic or atmospheric pattern can be reasonably well specified by the other. Patterns of oceanic thermal anomalies are about an order of magnitude more persistent than those of atmospheric circulations, and empirical studies have had some success in using sea surface temperature patterns in long-range weather prediction. In addition to empirical studies, efforts continue in the development of numerical-dynamical models in order to understand the complex linkages of the large-scale air-sea system.