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Global Warming and the Intensification of Rainfall Events

Hossain, F., Jeyachandran, I. and Pielke Sr., R. 2009. Have large dams altered extreme precipitation patterns? EOS, Transactions, American Geophysical Union 90: 453-454.
In their book entitled Dire Predictions: Understanding Global Warming, Mann and Kump (2008) write that most climate model simulations indicate that "increases are to be expected in the frequency of very intense rainfall events," and that although "many regions are likely to become drier, it is predicted that even in those regions individual rainfall events will become more intense."

In a study that might at first appear to be totally unrelated to this subject, Hossain et al. (2009) review and discuss meteorological effects that have been observed to occur in response to the impounding of water behind large dams.

The three researchers begin by noting that "in the United States alone, about 75,000 dams are capable of storing a volume of water equaling almost 1 year's mean runoff of the nation (Graf, 1999)," and that "at least 45,000 large dams have been built worldwide since the 1930s." They also indicate that "dam-driven land cover change can trigger changes in extreme precipitation patterns," citing the fact that Avissar and Liu (1996) demonstrated that land use and land cover [LULC] patchiness "can enhance heavy rainfall." Likewise, they report that "through LULC sensitivity studies (Pielke et al., 1997; Pielke and Zeng, 1989; Pielke et al., 2007), irrigated land near multipurpose reservoirs is seen to enhance thunderstorm development more than natural land cover conditions do (e.g., before the dam was built)," adding that "Kistawal et al. (2009) recently showed that increased urbanization downstream of large flood control dams can also trigger heavy rainfall patterns."

In additional findings suggestive of the phenomenon they describe, Hossain et al. (2009) report that Hossain et al. (2010) and Hossain (2010) have shown that "extreme precipitation (99th percentile) has increased considerably more than increases seen in median precipitation (50th percentile) during the past century," and that "this alteration may be more pronounced in arid and semiarid regions after the dam is built," noting that "large dams in the regions of southern Africa, India, western United States, and Central Asia appeared to induce a greater increase in extreme precipitation than in other regions."

Although there is a clear correlation between the development of large dams throughout the world and subsequent increases in extreme precipitation, the three scientists state in a cautionary note that "other factors may [also] be involved, such as global climate change." And such could well be true. But one typically doesn't hear the opposite, i.e., climate alarmists acknowledging that increases in extreme precipitation events might partly be induced by something other than global warming. So in comparing the objectivity of the two groups of scientists, it would appear that climate alarmists are less likely to entertain the possibility that views contrary to their own might possibly be even partially correct.

Additional References
Avissar, R. and Liu, Y. 1996. Three-dimensional numerical study of shallow convective clouds and precipitation induced by land surface forcing. Journal of Geophysical Research 101: 7499-7518.

Graf, W.L. 1999. Dam nation: A geographic census of American dams and their large-scale hydrologic impacts. Water Resources Research 35: 1305-1311.

Hossain, F. 2010. On the empirical relationship between the presence of large dams and the alteration in extreme precipitation. Natural Hazards Review 11: 97-101.

Hossain, F., Jeyachandran, I. and Pielke Sr., R. 2010. Dam safety effects due to human alteration of extreme precipitation. Water Resources Research 46: 10.1029/2009WR007704.

Kishtawal, C.M., Niyogi, D., Tewari, M., Pielke Sr., R.A. and Shepherd, J.M. 2009. Urbanization signature in the observed heavy rainfall climatology over India. International Journal of Climatology: 10.1002/joc.2044.

Mann, M.E. and Kump, L.R. 2008. Dire Predictions: Understanding Global Warming. DK Publishing, Inc., New York, New York, USA.

Pielke Sr., R.A., Adegoke, J., Beltran-Przekurat, A., Hiemstra, C.A., Lin, J., Nair, U.S., Niyogi, D. and Nobis, T.E. 2997. An overview of regional land use and land cover impacts on rainfall. Tellus Series B 59: 587-601.

Pielke Sr., R.A., Lee, T.J., Copeland, J.H., Eastman, J.L., Ziegler, C.L. and Finley, C.A. 1997. Use of USGS-provided data to improve weather and climate simulations. Ecological Applications 7: 3-21.

Pielke Sr., R.A. and Zeng, X. 1989. Influence on severe storm development of irrigated land. National Weather Digest 14: 16-17.

Archived 7 December 2010