July 1, 2011

Extreme Precipitation Update

Filed under: Climate Extremes

We definitely have seen some impressive and destructive storms across the United States this spring, and to no one’s surprise, the greenhouse crusade is claiming more evidence of global warming. A web search for “Extreme Precipitation and Global Warming” yields nearly 200,000 sites almost all proclaiming that heavy rain, hail, heavy snow, or even no extreme precipitation at all should all be blamed on global warming.

We have addressed this issue many times in the past, but recently, more articles have appeared in leading journals with news that might surprise global warming advocates.

The first was produced by a trio of scientists from Peking University and the University of Hawaii who must not have received the memo on global warming and extreme precipitation events as they state “The question remains as to whether hail size has been changing in response to the warming climate” (go look up “Global Warming and Hail” and enjoy 50,000 sites on the subject). Xie et al. collected hail size information from stations throughout China and at the end of their analyses, they state “Here, we found no significant long-term trend in hail size based on the proportion of severe hail indirectly in the four regions in China, suggesting that hail size, as an important aspect of hail climatology, may not be sensitive to the intrinsic natural variability or climate change in the last 2–3 decades.” Oops, another failure to link extreme precipitation to global warming.

Next up is an article by Chu et al. on extreme precipitation in Hawaii; funding was received from the National Park Service Task Agreement between the Joint Institute for Marine and Atmospheric Research and the National Oceanic and Atmospheric Administration. The scientists begin noting that “According to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, the rate of the global average surface temperature increased by 0.074ºC ± 0.018ºC decade-1 over the past 100 yr (1906–2005). Since 1981, the rate of warming is faster, with a value of approximately 0.177ºC ± 0.052ºC decade-1. Consistent with the global warming trend, Hawaii temperature experienced an upward trend as well: 0.043ºC decade-1 for the period of 1919–2006 and 0.163ºC decade-1 for the past 30 yr.” Furthermore, and consistent with 200,000 websites, they state “Under this warming background, it is expected that extreme events in temperature and precipitation, such as heat waves and heavy rainfall, are changing over time. The occurrence of extreme events is usually a concern for society because of their potential damage to humans, property, public infrastructure, agriculture, and others.”

Chu et al. collected data on extreme precipitation events from the various islands, and their results might surprise the universe outside of World Climate Report. Chu et al. conclude “Annual probability density functions of precipitation-related indices for two different epochs (i.e., 1950–79 and 1980– 2007) show a reduction in the probability of moderate and high precipitation intensity accompanied by an increase in light intensity, shorter annual total number of days with daily precipitation greater than 25.4 mm, and smaller annual maximum consecutive 5-day precipitation amounts from the first epoch to the second epoch. For the dryness indicator, the right tail of the distribution becomes heavier in the recent epoch, implying a lengthening of annual maximum number of consecutive dry days.” Extreme precipitation in Hawaii is declining, not increasing a bit. This is further demonstrated by formal trend analyses; they conclude “Using the Mann–Kendall test and Sen’s method, trends of water year and winter season of various periods have been investigated to further understand the long-term variations of those indices. Long-term downward trends are noted for precipitation-related indices and upward trend for drought-related index from the 1950s to the present.”

Are we are seeing a pattern here – expect more extreme precipitation, conduct analyses, and conclude extreme precipitation is not increasing?

Increases in extreme precipitation should also be causing extreme flooding, all thanks to global warming. A team of German and French scientists decided to have a look at the situation in Europe, and they begin their article curiously stating “Assumptions about an increase in extreme flood events due to an intensified hydrological cycle caused by global warming are still under discussion and must be better verified. Statistical flood analyses indicate that simple mechanistic explanations are not straightforward and that complex seasonal and regional effects have to be considered. Some historical flood records even indicate that flood frequencies were higher during colder periods, challenging the hypothesis of a correlation between the frequency of extreme floods and a warmer climate.” We knew we were going to like this one!

To make a long story short, Czymzik et al. examined sediment deposits in a well-situated lake in southern Germany, and they found the sediments beautifully preserved flood events from the past. Consistent with what others had found, this team concluded that flood “frequency distribution over the entire 450 year time series is not stationary but reveals maxima for colder periods of the Little Ice Age when solar activity was reduced.” That is something we see over and over – extreme events occurring in cold periods, not warm ones.

In light of the above, and from the plethora of other studies which fail to find a human influence of extreme weather, we’ll leave you with this incredible one sentence summary of an article by Laurens Bouwer in the Bulletin of the American Meteorological Society – a statement that still has us shaking our heads:

“Lacking significant impact from anthropogenic warming so far, the best way to assess the potential influence of climate change on disaster losses may be to analyze future projections rather than historical data.”

So we should disregard the lessons from past data on hail in China, extreme precipitation events in Hawaii, floods in southern Germany, or the historical occurences of other extreme weather, and instead turn to climate model projections for guidance? We can only hope that he is kidding.

References:

Bouwer, L.M. 2011. Have Disaster Losses Increased Due to Anthropogenic Climate Change? Bulletin of the American Meteorological Society, 92, 39-46.

Chu, P.-S., Y.R. Chen, and T.A. Schroeder. 2010. Changes in Precipitation Extremes in the Hawaiian Islands in a Warming Climate. Journal of Climate, 23, 4881-4900.

Czymzik, M., P. Dulski, B. Plessen, U. von Grafenstein, R. Naumann, and A. Brauer. 2010. A 450 Year Record of Spring‐Summer Flood Layers in Annually Laminated Sediments from Lake Ammersee (Southern Germany), Water Resources Research, 46, W11528, doi:10.1029/2009WR008360.

Xie, B., Q. Zhang, and Y. Wang. 2010. Observed Characteristics of Hail Size in Four Regions in China during 1980–2005. Journal of Climate, 23, 4973-4982.




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