Lins and Slack (1999) analyzed secular trends in streamflow for 395 climate-sensitive stream gage stations (including data from more than 1500 individual gages) located throughout the conterminous United States, some of which stations possessed data sets stretching all the way back to 1914. In doing so, they found many more up-trends than down-trends in streamflow nationally, with slight decreases "only in parts of the Pacific Northwest and the Southeast." These and other of their findings, as they describe them, indicate "the conterminous U.S. is getting wetter, but less extreme [our italics]," and it is difficult to conceive of a better result. As the world has warmed over the past century, the United States has gotten wetter in the mean, but less variable at the extremes, where floods and droughts occur.

Also studying the conterminous United States were McCabe and Wolock (2002), who for the period 1895-1999 evaluated (1) precipitation minus annual potential evapotranspiration, (2) the surplus water that eventually becomes streamflow, and (3) the water deficit that must be supplied by irrigation to grow vegetation at an optimum rate. This exercise revealed there was a statistically significant increase in the first two of these parameters, while for the third there was no change, indicative of the fact that over the period of time climate alarmists describe as having witnessed a global warming that was unprecedented over the past one to two millennia (which they claim is leading to catastrophic moisture-related consequences for agriculture), water has actually become more available within the conterminous United States, and there has been no increase in the amount of water required for optimum plant growth.

Knox (2001) studied how conversion of the U.S. Upper Mississippi River Valley from prairie and forest to crop and pasture land by settlers in the early 1800s influenced subsequent watershed runoff and soil erosion rates. Initially, the conversion of the region's natural landscape to primarily agricultural use boosted surface erosion rates to values three to eight times greater than those characteristic of pre-settlement times. In addition, the land-use conversion increased peak discharges from high-frequency floods by 200 to 400%. Since the late 1930s, however, surface runoff has been decreasing; but the decrease "is not associated with climatic causes," according to Knox, who reports that "an analysis of temporal variation in storm magnitudes for the same period showed no statistically significant trend."

Other notable findings of Knox's study include the observation that since the 1940s and early 1950s, the magnitudes of the largest daily flows have been decreasing at the same time that the magnitude of the average daily baseflow has been increasing, indicating a trend toward fewer flood and drought conditions. Once again, therefore, we have a situation where global warming has coincided with a streamflow trend that is leading to the best of all possible worlds, i.e., one of greater water availability, but with fewer and smaller floods and droughts.

Molnar and Ramirez (2001) conducted a detailed watershed-based analysis of precipitation and streamflow trends for the period 1948-97 in a semiarid region of the southwestern United States, the Rio Puerco Basin of New Mexico. "At the annual timescale," as they describe it, "a statistically significant increasing trend in precipitation in the basin was detected." This trend was driven primarily by an increase in the number of rainy days in the moderate rainfall intensity range, with essentially no change at the high-intensity end of the spectrum. In the case of streamflow, however, there was no trend at the annual timescale; but monthly totals increased in low-flow months and decreased in high-flow months.

What are the implications of these findings? Increasing precipitation in a semiarid region sounds like a plus to us. Having most of the increase in the moderate rainfall intensity range also sounds like a plus. Increasing streamflow in normally low-flow months sounds good as well, as does decreasing streamflow in high-flow months. In fact, what more could one possibly want in terms of changes in precipitation and streamflow? ... especially in a world that according to the anti-CO2 forces of the planet is supposed to be experiencing more extreme weather events and increases in floods and droughts? We once thought that by predicting both more floods and more droughts at one and the same time in response to global warming, climate alarmists were making sure they could not be proven wrong in their predictions of CO2-induced water-related calamities. In reviewing what nature reveals about the matter, however, it seems we erred in this assumption; they can be wrong on both counts, and they oftentimes are.

Shifting to a study of snowmelt runoff (SMR), McCabe and Clark (2005) note that most prior studies of this phenomenon in the western United States have depended on trend analyses to identify changes in timing, but they indicate that "trend analyses are unable to determine if a trend is gradual or a step change." This fact is crucial, they say, because when "changes in SMR timing have been identified by linear trends, there is a tendency to attribute these changes to global warming because of large correlations between linear trends in SMR timing and the increasing trend in global temperature." Therefore, using daily streamflow data for 84 stations in the western U.S., each with complete water-year information for the period 1950-2003, they conducted a number of analyses that enabled them to determine each station's mean streamflow trend over the last half century, as well as any stepwise changes that may have occurred in each data series.

As others before them had previously learned, the two researchers found that "the timing of SMR for many rivers in the western United States has shifted to earlier in the snowmelt season." However, they discovered that "the shift to earlier SMR has not been a gradual trend, but appears to have occurred as a step change during the mid-1980s," which shift was "related to a regional step increase in April-July temperatures during the mid-1980s." As a result, and after discussing various other possible reasons for what they had discovered, McCabe and Clark concluded that "the observed change in the timing of SMR in the western United States is a regional response to natural climatic variability and may not be related to global trends in temperature."

Over in Minnesota, Novotny and Stefan (2006) analyzed streamflow records (extending up to the year 2002, with lengths ranging from 53 to 101 years) obtained from 36 gauging stations in five major river basins of the state, deriving histories of seven annual streamflow statistics: "mean annual flow, 7-day low flow in winter, 7-day low flow in summer, peak flow due to snow melt runoff, peak flow due to rainfall, as well as high and extreme flow days (number of days with flow rates greater than the mean plus one or two standard deviations, respectively)." In doing so, they found significant trends in each of the seven streamflow statistics throughout the state, but that in most cases "the trends are not monotonic but periodic," and they determined, as might have been expected, that "the mean annual stream flow changes are well correlated with total annual precipitation changes."

Most significantly, they found that peak flood flows due to snowmelt runoff "are not changing at a significant rate throughout the state," but that 7-day low flows or base flows are "increasing in the Red River of the North, Minnesota River and Mississippi River basins during both the summer and winter," that the "low flows are changing at a significant rate in a significant number of stations and at the highest rates in the past 20 years," and that "this finding matches results of other studies which found low flows increasing in the upper Midwest region including Minnesota (Lins and Slack, 1999; Douglas et al., 2000)."

With respect to the ramifications of their findings, the two researchers write than "an increase in mean annual streamflow in Minnesota would be welcome," as "it could provide more aquatic habitat, better water quality, and more recreational opportunities, among other benefits." Likewise, they say 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." In addition, they say "other good news is that spring floods (from snowmelt), the largest floods in Minnesota, have not been increasing significantly." Clearly, therefore, even in the fabled "Land of Ten Thousand Lakes," increasing base flows of rivers and streams are tending to enhance the environment, in response to - or in spite of (take your pick) - the supposedly unprecedented increases in air temperature and atmospheric CO2 concentration that have been experienced concurrently.

In a study that covered parts of two countries, Rood et al. (2005) performed an empirical analysis of streamflow trends for rivers fed by relatively pristine watersheds in the central Rocky Mountain Region of North America that extends from Wyoming in the United States through British Columbia in Canada. In doing so, they applied both parametric and non-parametric statistical analyses to assess nearly a century of annual discharge (ending about 2002) along 31 river reaches that drain this part of North America. These analyses revealed that river flows in this region declined over the past century by an average of 0.22% per year, with four of them exhibiting recent decline rates exceeding 0.5% per year. This finding, in the words of Rood et al., "contrasts with the many current climate change predictions that [this specific] region will become warmer and wetter in the near-future." Once again, therefore, the models appear to have gotten it all wrong for a large portion of North America.

Working entirely in Canada, where about three quarters of the country is drained by rivers that discharge their water into the Arctic and North Atlantic Oceans, Déry and Wood (2005) analyzed hydrometric data from 64 northern Canadian rivers that drain more than half of the country's landmass for the period 1964-2003. Then, after assessing both variability and trends, they explored the influence of large-scale teleconnections as possible drivers of the trends they detected. This work indicated there was a statistically significant mean decline of approximately10% in the discharge rates of the 64 rivers over the four decades of their study, which was nearly identical to the decline in precipitation falling over northern Canada between 1964 and 2000. These facts led the two scientists to conclude that the changes in river discharge they observed were driven "primarily by precipitation rather than evapotranspiration." As for the cause of the precipitation/river discharge decline, statistically significant links were found between the decline and the Arctic Oscillation, the El Niño/Southern Oscillation and the Pacific Decadal Oscillation. Consequently, the results of this study indicate there is nothing unusual about the four-decade-long trends in northern Canada river discharge rates, which means there is nothing in these trends that would suggest a global warming impact. If anything, the results argue against the worrisome climate-alarmist notion, for state-of-the-art climate models generally suggest that global warming will enhance river discharge rates due to an intensified hydrologic cycle. The trends observed here, however, are just the opposite; and it would appear they are the products of natural variations in natural phenomena.

In a final study from Canada, St. George (2007) begins by noting that the study of Burn (1994) suggested that a doubling of the air's CO2 content could increase the severity and frequency of droughts in the prairie provinces of Canada (Alberta, Saskatchewan, Manitoba), but that results from an ensemble of climate models suggest that runoff in the Winnipeg River region of southern Manitoba, as well as runoff in central and northern Manitoba, could increase 20-30% by the middle of the 21st century (Milly et al., 2005). To help resolve this dichotomy, St. George obtained daily and monthly streamflow data from nine gauge stations within the Winnipeg River watershed from the Water Survey of Canada's HYDAT data archive, plus precipitation and temperature data from Environment Canada's Adjusted Historical Canadian Climate Data archive, and analyzed them for trends over the period 1924-2003.

This work revealed, in the words of St. George, that "mean annual flows have increased by 58% since 1924 ... with winter streamflow going up by 60-110%," primarily because of "increases in precipitation during summer and autumn." In addition, he notes that similar "changes in annual and winter streamflow are observed in records from both regulated and unregulated portions of the watershed, which point to an underlying cause related to climate." Countering these positive findings, however, St. George says there are "reports of declining flow for many rivers in the adjacent Canadian prairies," citing the studies of Westmacott and Burn (1997), Yulianti and Burn (1998), Dery and Wood (2005) and Rood et al. (2005). Consequently, just as there are conflicting predictions about the future water status of portions of the Prairie Provinces of Canada, especially in Manitoba, so too are there conflicting reports about past streamflow trends in this region. Hence, it's anybody's guess as to what will actually occur in the years and decades ahead, although based on the observed trends he discovered, St. George believes "the potential threats to water supply faced by the Canadian Prairie Provinces over the next few decades will not include decreasing streamflow in the Winnipeg River basin."

In concluding this brief summary, we note there appear to be few real-world data from North America that provide any significant support for the climate-alarmist contention that CO2-induced global warming will lead to more frequent and/or more severe increases and decreases in streamflow that result in, or are indicative of, more frequent and/or more severe floods and droughts. In fact, in the vast majority of cases, observed trends appear to be just the opposite of what people like super-climate-pessimists Al Gore and James Hansen are predicting. Not only are real-world observations nearly all not undesirable, they are positive, and typically extremely so.

References
Burn, D.H. 1994. Hydrologic effects of climate change in western Canada. Journal of Hydrology 160: 53-70.

Déry, S.J. and Wood, E.F. 2005. Decreasing river discharge in northern Canada. Geophysical Research Letters 32: doi:10.1029/2005GL022845.

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.

Knox, J.C. 2001. Agricultural influence on landscape sensitivity in the Upper Mississippi River Valley. Catena 42: 193-224.

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

McCabe, G.J. and Clark, M.P. 2005. Trends and variability in snowmelt runoff in the western United States. Journal of Hydrometeorology 6: 476-482.

McCabe, G.J. and Wolock, D.M. 2002. Trends and temperature sensitivity of moisture conditions in the conterminous United States. Climate Research 20: 19-29.

Milly, P.C.D., Dunne, K.A. and Vecchia, A.V. 2005. Global patterns of trends in streamflow and water availability in a changing climate. Nature 438: 347-350.

Molnar, P. and Ramirez, J.A. 2001. Recent trends in precipitation and streamflow in the Rio Puerco Basin. Journal of Climate 14: 2317-2328.

Novotny, E.V. and Stefan, H.G. 2006. Stream flow in Minnesota: Indicator of climate change. Journal of Hydrology 334: 319-333.

Rood, S.B., Samuelson, G.M., Weber, J.K. and Wywrot, K.A. 2005. Twentieth-century decline in streamflow from the hydrographic apex of North America. Journal of Hydrology 306: 215-233.

St. George, S. 2007. Streamflow in the Winnipeg River basin, Canada: Trends, extremes and climate linkages. Journal of Hydrology 332: 396-411.

Westmacott, J.R. and Burn, D.H. 1997. Climate change effects on the hydrologic regime within the Churchill-Nelson River Basin. Journal of Hydrology 202: 263-279.

Yulianti, J. and Burn, D.H. 1998. Investigating links between climatic warming and low streamflow in the Prairies region of Canada. Canadian Water Resources Journal 23: 45-60.