UMRBA – ORSANCO JOINT MEETING JUNE 2013. EXTREME WEATHER EVENTS AND CLIMATE CHANGE. Climate Change and Public Policy. Definition of Climate Change Impacts of Extreme Events Tools for Analysis Policy at local, state, regional and federal levels. Climate Change.
EXTREME WEATHER EVENTS
Published: Mar 16th, 2012
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Many studies have reported that total precipitation is increasing across the United States with most of the increase resulting from a positive trend in the upper tail of the daily precipitation distribution.
Other studies have found that low and moderate, but not high flows are also increasing across much of the United States. How can precipitation, especially that produced by intense events, increase without a corresponding increase in high flows?
We analyzed trends in annual 7-day low, average and high flows along with seasonal precipitation that is averaged over individual basins. Our findings suggest that statistically significant trends in both fall precipitation and 7-day low flow are found in a large percentage of the basins in the upper Mississippi and Great Lakes regions of the country.
A large fraction of the trends in annual precipitation can be explained by an increase in fall precipitation. By estimating trends in precipitation at the spatial scale of individual basins, we offer a simple explanation for the apparent paradox of lack of trends in high flows.
At the spatial scale of individual basins, precipitation is increasing during the fall but not during the spring, the season when high flows are generally observed. The increase in fall precipitation appears to result in an increase in the low flows while the lack of trends in precipitation in spring explains the lack of widespread trends in the high flows.
Pavel Ya Groisman, Richard W. Knight, Thomas R. Karl, David R. Easterling, Bomin Sun, and Jay H. Lawrimore National Climatic Data Center, Asheville, North Carolina
Over the contiguous United States, precipitation, temperature, streamflow, and heavy and very heavy precipitation have increased during the twentieth century. In the east, high streamflow has increased as well.
Soil wetness (as described by the Keetch–Byram Drought index) has increased over the northern and eastern regions of the United States, but in the southwestern quadrant of the country soil dryness has increased, making the region more susceptible to forest fires.
In addition to these changes during the past 50 yr, increases in evaporation, near-surface humidity, total cloud cover, and low stratiform and cumulonimbus clouds have been observed.
Snow cover has diminished earlier in the year in the west, and a decrease in near-surface wind speed has also occurred in many areas. Much of the increase in heavy and very heavy precipitation has occurred during the past three decades.
Received: May 2, 2003; Accepted: October 15, 2003
N. Y. Krakauer and I. Fung
University of California at Berkeley, USA
Received: 12 February 2008 – Published in Hydrol. Earth Syst. Sci. Discuss.: 19 March
We developed maps of annual streamflow anomalies over the coterminous United States using streamflow records selected to reflect minimum direct impacts from human land disturbance and water diversion. We find that streamflow increased around 1970 in concert with an increase in precipitation, but has not increased since then. Our analysis supports net drying in some regions, and no change in others, as a result of greenhouse warming, with tentative evidence for the opposing effects of warming and CO2 increase. Depending on how this interplay between temperature and direct CO2 effect of greenhouse gas emissions evolves, there is a high risk of reduced water supplies and increased plant water stress with continued warming in coming decades.
Acknowledgements. NYK thanks the National Oceanic and Atmospheric
Administration (NOAA) for a Climate and Global Change Postdoctoral Fellowship. IF acknowledges support from NOAA Office of Global Programs, Award NA05OAR4311167, and NSF, Award 0628678. We thank Marc Bierkens, Laurens Bouwer, Attilio Castellarin, and Shilong Piao for reviewing this paper during the Discussion stage; Alanood Alkhaled, Anna Michalak and Kim Mueller for geostatistics help; Boris Fain, Jim Hunt, Tom Pagano, and Alexander Stine for proofreading and useful suggestions; and Graham Farquhar, Chandra Pathak, Michael Roderick and Ramesh Teegavarapu for comments at a conference presentation of an earlier version of this work.
Edited by: B. van den Hurk
WE ARE AT INCREASED RISK OF UNPREDICTABLE CONDITIONS
Policies are still changing in regard to climate extremes
Flood of 2011
Flood of 2013
Drought of 2012
Published: Dec 13th, 2012
Climate Central did the math, and the numbers don't lie: 2012 will be the hottest U.S. year ever recorded, pushing 1998 into second place, followed by 2006, 1934 and 1999.
Geoffrey M. Bonnin, Deborah Martin, Bingzhang Lin, Tye