We have two new papers that document a role of land management (in this case the effect of reservoirs and changes in landscape around a large dam) on extreme rainfall.
The papers are:
Hossain, F., I. Jeyachandran, and R.A. Pielke Sr., 2009: Have large dams altered extreme precipitation patterns during the last Century? Eos, Vol. 90, No. 48, 453-454. Copyright (2009) American Geophysical Union.
Hossain, F., I. Jeyachandran, and R.A. Pielke Sr., 2009: Dam safety effects due to human alteration of extreme precipitation. Water Resources Research, doi:10.1029/2009WR007704, in press.
The conclusion of the second paper reads
“Today, we know little about the impact of dams and reservoirs on the alteration in precipitation patterns as we step into the 21st century. Dam design protocol in civil engineering continues to assume as ‘static’ the statistical parameters of a low exceedance probability precipitation event during the life-span of the dam. Our study seems to indicate that the impact of large dams on extreme precipitation is clearly a function of surrounding meso-scale and land-use conditions (e.g., see Pielke et al., 2007; Douglas et al 2009), and that more research is necessary to gain insights on the physical mechanisms of extreme precipitation alteration by dams. The changes in land-use, for example from added irrigation, add a significant amount of water vapor into the atmosphere in the growing season, thereby fueling showers and thunderstorms (e.g. see Pielke and Zeng, 1989; Pielke et al 1997; Pielke 2001). Such landscape changes can even alter large scale precipitation patterns such as the Asian monsoon (e.g. see Takata et al, 2009).
Although, the focus of our paper is primarily on how dams may alter extreme precipitation patterns and consequentially the flood frequency relationship, we should also recognize that there are other direct ways that the discharge into a reservoir may increase in frequency and magnitude (such as urbanization and other changes in land cover). Whatever the possible causes might be, it is timely for the civil engineering profession to change perceptions and embrace an interactive hydrology/atmospheric science approach to safe dam design and operations for the 21st century.
There has been news coverage of our articles, including