Understanding and managing the impacts of climate change in a complex environmental system: The effects of increasing precipitation and land use change on streamflow.

摘要

Increased variability in the hydrologic cycle, including more extreme rainstorms and flood events, is anticipated as a result of global climate change. These variations may be exacerbated by alterations within watershed boundaries, such as land use change. In order to determine the relative impacts of precipitation and land use change on streamflow, spatial and temporal trends in precipitation and streamflow were examined for small watersheds throughout the United States, with particular emphasis on Midwestern regional and local changes. In the 160 watersheds selected for analysis, only nineteen sites had increasing trends in both precipitation and streamflow and increasing trends in peak streamflow were more than twice as prevalent as increasing trends in peak precipitation, indicating that many peak streamflow increases were not driven by changes in peak precipitation events. Seasonal analysis of peak daily precipitation and streamflow data in the Midwest indicated that half of all study sites had significant (alpha = 0.05) increasing trends in peak fall streamflow and nearly 40% of sites had significant trends in peak daily precipitation. This high number of sites with increases greatly overshadowed the number of sites with significant changes occurring in other seasons, and were significantly impacted by the level of watershed imperviousness; watersheds with impervious levels exceeding sixteen percent had greater increases in peak fall streamflow. Additional analysis of precipitation records in the Midwest indicated that precipitation statistics commonly used in engineering design are outdated, with increases in design storm event depths becoming greater over time, even though trends in peak precipitation events are not significantly increasing. Such changes in precipitation and streamflow require adaptive water resource plans to be in place for communities and agricultural areas, since stationarity in the quantity and quality of hydrologic resources cannot be assumed under climate and land use changes present in many parts of the U.S.