The world's climate alarmists claim that both droughts and floods will be more common, as well as more severe and long-lasting, in a CO2-enriched warmer world, and that such is already occurring around the globe. Already several years ago, for example, Hisdal et al. (2001) noted that "the media often reflect the view that recent severe drought events are signs that the climate has in fact already changed owing to human impacts." Hence, they and others have been studying data from throughout Eurasia for evidence to either support or refute this contention. In this brief Summary, we review what has been learned from their efforts to date.
Hisdal et al. (2003) examined what the data show for Europe. Specifically, they performed a series of statistical analyses on more than 600 daily streamflow records from the European Water Archive to examine trends in the severity, duration and frequency of drought over the following four time periods: 1962-1990, 1962-1995, 1930-1995, and 1911-1995. This protocol indicated that "despite several reports on recent droughts in Europe, there is no clear indication that streamflow drought conditions in Europe have generally become more severe or frequent in the time periods studied." Quite to the contrary, they report discovering that the number of trends pointing towards decreasing streamflow deficits or fewer drought events exceeded the number of trends pointing towards increasing drought deficits or more drought events.
Looking towards Asia, Cluis and Laberge (2001) utilized streamflow records stored in the databank of the Global Runoff Data Center at the Federal Institute of Hydrology in Koblenz (Germany) to see if there were any recent changes in river runoff of the type predicted by IPCC scenarios of global warming, such as increased streamflow and increases in streamflow variability that would lead to more floods and droughts. Spatially, their study encompassed 78 rivers said to be "geographically distributed throughout the whole Asia-Pacific region," while temporally the mean start and end dates of the river flow records were 1936 ± 5 years and 1988 ± 1 year.
As a result of their analyses, the two researchers determined that mean river discharges were unchanged in 67% of the cases investigated; and where trends did exist 69% of them were downward. Likewise, maximum river discharges were unchanged in 77% of the cases investigated; and where trends did exist 72% of them were downward. Minimum river discharges, on the other hand, were unchanged in 53% of the cases investigated; while where trends did exist 62% of them were upward.
With respect to the implications of these findings, we note that in the case of mean river discharge, the empirical observations go doubly against climate-alarmist predictions, i.e., most rivers show no change in flow volume, while most of those that do show changes exhibit decreases. In the case of maximum river discharge, the empirical observations also go doubly against climate-alarmist predictions, i.e., most rivers show no change in flow volume, while most of those that do exhibit changes show decreases, indicative of the likelihood of less flooding. Finally, in the case of minimum river discharge, the empirical observations once again go doubly against climate alarmist predictions, i.e., most rivers show no change in flow volume, while most of those that do exhibit changes show increases, indicative of the likelihood of less drought. Consequently, out of six possible metrics related to streamflow trends, all six exhibit changes that are contrary to IPCC-promoted scenarios of climate change.
Writing about the Qinghai-Tibet Plateau, where they conducted their streamflow study, Cao et al. (2006) note that "both theoretical arguments and models suggest that net high-latitude precipitation increases in proportion to increases in mean hemispheric temperature (Houghton et al., 2001; Rahmstorf and Ganopolski, 1999; Bruce et al., 2002)," stating that in these scenarios "under global warming, mainly in the middle and west regions of northwest China, precipitation increases significantly," so that "some researchers [have] even advanced the issue of [a] climatic shift from warm-dry to warm-wet in northwest China (Shi, 2003)," with the ultimate expectation that total river discharge within the region would significantly increase in response to global warming.
As a test of these climate-model predictions, Cao et al. analyzed annual discharge data for five large rivers of the Qinghai-Tibet Plateau over the period 1956-2000, using the Mann-Kendall nonparametric trend test; and in doing so, they found that over the period of their study, "river discharges in the Qinghai-Tibet Plateau, in general, have no obvious change with the increase of the Northern Hemisphere surface air temperature." Hence, because they could detect, in their words, "no increase in the stream discharge in the Qinghai-Tibet Plateau with global warming," Cao et al. concluded that their real-world findings are not "in accordance with the anticipated ideas" that led them to conduct their study. Indeed, the disconnect between streamflow and global warming in this and many other studies argues strongly against either (1) the claimed consequences of global warming or (2) the claimed large magnitude of global warming or (3) both of these standard climate-alarmist claims.
Last of all, worried about the possibility that enhanced freshwater delivery to the Arctic ocean by increased river flow could shut down the ocean's thermohaline circulation, Peterson et al. (2002) plotted annual values of the combined discharge of the six largest Eurasian Arctic rivers (Yenisey, Lena, Ob', Pechora, Kolyma and Severnaya Dvina) - which drain about two-thirds of the Eurasian Arctic landmass - against the globe's mean annual surface air temperature (SAT), after which they ran a simple linear regression through the data and determined that the combined discharge of the six rivers seems to rise by about 212 km3/year in response to a 1°C increase in mean global air temperature. Then, they calculated that for the high-end global warming predicted by the Intergovernmental Panel on Climate Change (IPCC) to occur by AD 2100, i.e., a temperature increase of 5.8°C, the warming-induced increase in freshwater discharge from the six rivers could rise by as much as 1260 km3/year (we calculate 5.8°C x 212 km3/year/°C = 1230 km3/year), which represents a 70% increase over the mean discharge rate of the last several years.
The link between this conclusion and the postulated shutting down of the thermohaline circulation of the world's oceans resides in the hypothesis that the delivery of such a large addition of freshwater to the North Atlantic Ocean may slow - or even stop - that location's production of new deep water, which constitutes one of the driving forces of the great oceanic "conveyor belt." Although still discussed, this scenario is currently not as highly regarded as it was when Peterson et al. conducted their research, for a number of reasons, one that we have highlighted being the difficulty of accepting the tremendous extrapolation Peterson et al. make in extending their Arctic freshwater discharge vs. SAT relationship to the great length that is implied by the IPCC's predicted high-end warming of 5.8°C over the remainder of the current century.
Consider, for example, that "over the period of the discharge record, global SAT increased by [only] 0.4°C," according to Peterson et al. Do you think it reasonable to extend the relationship they derived across that small temperature range fully fourteen and a half times further? We surely don't, nor should any other rational person.
Consider also the Eurasian river discharge anomaly vs. global SAT plot of Peterson et al. (their Figure 4), which we have replotted in the figure below. Enclosing their data with simple straight-line upper and lower bounds, it can be seen that the upper bound of the data does not change over the entire range of global SAT variability, suggesting the very real possibility that the upper bound corresponds to a maximum Eurasian river discharge rate that cannot be exceeded in the real world under its current geographic and climatic configuration. The lower bound, on the other hand, rises so rapidly with increasing global SAT that the two bounds intersect less than two-tenths of a degree above the warmest of Peterson et al.'s 63 data points, suggesting that 0.2°C beyond the temperature of their warmest data point may be all the further any relationship derived from their data may validly be extrapolated.
Annual Eurasian Arctic river discharge anomaly vs. annual global surface air temperature (SAT) over the period 1936 to 1999. Adapted from Peterson et al. (2002).
In considering these observations, plus the findings of the other papers reviewed in this Summary, we feel it is obvious that real-world data do not support the hydrologic negativism climate alarmists associate with both real-world and simulated global warming.
References
Bruce, J.P., Holmes, R.M., McClelland, J.W. et al. 2002. Increasing river discharge to the Arctic Ocean. Science 298: 2171-2173.
Cao, J., Qin, D., Kang, E. and Li, Y. 2006. River discharge changes in the Qinghai-Tibet Plateau. Chinese Science Bulletin 51: 594-600.
Cluis, D. and Laberge, C. 2001. Climate change and trend detection in selected rivers within the Asia-Pacific region. Water International 26: 411-424.
Hisdal, H., Stahl, K., Tallaksen, L.M. and Demuth, S. 2001. Have streamflow droughts in Europe become more severe or frequent? International Journal of Climatology 21: 317-333.
Houghton, J.T., Ding, Y., Griggs, D.J., Eds. Climate Change 2001: The Scientific Basis. Cambridge University Press, Cambridge.
Peterson, B.J., Holmes, R.M., McClelland, J.W., Vorosmarty, C.J., Lammers, R.B., Shiklomanov, A.I., Shiklomanov, I.A. and Rahmstorf, S. 2002. Increasing river discharge to the Arctic Ocean. Science 298: 2171-2173.
Rahmstorf, S. and Ganopolski, A. 1999. Long-term global warming scenarios computed with an efficient coupled climate model. Climatic Change 43: 353-367.
Shi, Y. 2003. An Assessment of the Issues of Climatic Shift from Warm-Dry to Warm-Wet in Northwest China. Meteorological Press, Beijing.
Last updated 19 September 2007