Science Source

Heavy Precipitation and High Streamflow in the Contiguous United States: Trends in the Twentieth Century

States that changes in several components of the hydrological cycle over the contiguous United States have been documented during the twentieth century: an increase of precipitation, especially heavy and very heavy precipitation, and a significant retreat in spring snow cover extent over western regions during the last few decades
States that these changes have affected streamflow, including the probability of high flow
Finds a significant relationship between the frequency of heavy precipitation and high streamflow events in the eastern half of the United States both annually and during the months of maximum streamflow
Identifies two factors that contributed to finding such a relation: 1) the relatively small contribution of snowmelt to heavy runoff in the eastern United States (compared to the west), and 2) the presence of a sufficiently dense network of streamflow and precipitation gauges available for analysis
Finds an increase of spring heavy precipitation events over the eastern United States indicates with high probability that during the twentieth century an increase of high streamflow conditions has also occurred
In the West, a statistically significant reduction of snow cover extent has complicated the relation between heavy precipitation and streamflow
Increases in peak stream flow have not been observed here, despite increases in heavy precipitation events, and less extensive snow cover is the likely cause