What was done
The authors studied streamflow records (up to the year 2002) from 36 U.S. Geological Survey gauging stations in five major river basins of Minnesota, USA: Red River of the North, Rainy River, Mississippi River, Minnesota River and tributaries to Lake Superior. Seven of the stations had record lengths in excess of 90 years, eleven had lengths of 70 to 90 years, and eighteen had lengths of 50 to 70 years.

What was learned
Novotny and Stefan report that "increases in low flow (base flow) in summer and in winter have been significant," while "peak flow due to snowmelt, typically the highest flow in each year ... has not changed at a significant rate."

What it means
In discussing the implications of their findings, the two researchers rhetorically ask: "What do these changes mean for the future of the water resources in the State of Minnesota?" Answering their own question, they say that "higher summer and winter base flows may benefit water quality," as well as "provide more aquatic habitat ... and more recreational opportunities, among other benefits," stressing that "water quality and aquatic ecosystems should benefit from increases in low flows in both the summer and winter since water quality stresses are usually largest during low flow periods."

"The other good news," as they continue, "is that spring floods (from snowmelt), the largest floods in Minnesota, have not been increasing significantly." Hence, it would appear that Minnesota is experiencing the best of both worlds when it comes to the hydrologic extremes of low flows and large floods. The former are rising significantly while the latter are not, as the researchers note has typically been observed throughout the entire United States, citing the broader-based studies of Lins and Slack (1999) and Douglas et al. (2000).

Not much apocalyptic gore here!

References
Douglas, E.M., Vogel, R.M. and Kroll, C.N. 2000. Trends in floods and low flows in the United States: impact of spatial correlation. Journal of Hydrology 240: 90-105.

Lins, H.F. and Slack, J.R. 1999. Streamflow trends in the United States. Geophysical Research Letters 26: 227-230.