Climate alarmists claim CO2-induced global warming will adversely impact earth's water resources by inducing large changes in global streamflow characteristics. As a result, many scientists are examining proxy streamflow records in an effort to determine how temperature changes of the 20th century may or may not have impacted this aspect of the planet's hydrologic cycle. We here review some of their findings that pertain to Eurasia, seeking to discover if there have been any 20th-century changes in streamflow regimes in this part of the world that might reasonably have been caused by 20th-century changes in air temperature and atmospheric CO2 concentration, which latter changes the world's climate alarmists typically characterize as having been unprecedented (or nearly so) over thousands of years to hundreds of thousands of years, respectively.
Pederson et al. (2001) used tree-ring chronologies from northeastern Mongolia to develop annual precipitation and streamflow histories for the period 1651-1995. This work revealed, with respect to both standard deviations and 5-year intervals of extreme wet and dry periods, that "variations over the recent period of instrumental data are not unusual relative to the prior record," although they say that the reconstructions "appear to show more frequent extended wet periods in more recent decades." Nevertheless, they state that this observation "does not demonstrate unequivocal evidence of an increase in precipitation as suggested by some climate models." Spectral analysis of the data also revealed significant periodicities of 12 and 20-24 years, suggesting, in the researchers' words, "possible evidence for solar influences in these reconstructions for northeastern Mongolia."
Working in another part of the same region, Davi et al. (2006) report that "absolutely dated tree-ring-width chronologies from five sampling sites in west-central Mongolia were used in precipitation models and an individual model was made using the longest of the five tree-ring records (1340-2002)," which effort led to a reconstruction of streamflow that extended from 1637 to 1997. In analyzing these data, the four researchers discovered there was "much wider variation in the long-term tree-ring record than in the limited record of measured precipitation," which for the region they studied covered the period from 1937 to 2003. In addition, they report their streamflow history indicates that "the wettest 5-year period was 1764-68 and the driest period was 1854-58," while "the most extended wet period [was] 1794-1802 and ... extended dry period [was] 1778-83." For this part of Mongolia, therefore - which the researchers say "is representative of the central Asian region" - there is no support to be found for the climate-alarmist contention that the "unprecedented" warming of the 20th century has led to increased variability in precipitation and streamflow.
Rounding out our short Summary, Pekarova et al. (2003) analyzed the annual discharge rates of selected large rivers of the world for recurring cycles of wet and dry periods. For those rivers with sufficiently long and accurate data series, they also derived long-term discharge rate trends. This latter analysis, however, did not show "any significant trend change in long-term discharge series (1810-1990) in representative European rivers," including the Goeta, Rhine, Neman, Loire, Wesaer, Danube, Elbe, Oder, Vistule, Rhone and Po.
These latter observations are most interesting, for they indicate that even over the 180-year time period that saw the demise of the Little Ice Age and the ushering in of the Current Warm Period, there were no long-term trends in the discharge rates of the major rivers of Europe. Does this observation suggest earth's hydrologic cycle may not be as sensitive to global warming as climate alarmists claim it is? It's difficult to say for sure, due to inadequate river discharge data from many parts of the world; but the discharge data of Europe's major rivers sure don't support the contention.
In light of the results of these three important studies, it would thus appear that the supposedly "unprecedented" 20th-century increases in global air temperature and atmospheric CO2 concentration have not led to commensurate changes in streamflow throughout large parts of Eurasia. In fact, we do not see any changes at all.
References
Davi, N.K., Jacoby, G.C., Curtis, A.E. and Baatarbileg, N. 2006. Extension of drought records for Central Asia using tree rings: West-Central Mongolia. Journal of Climate 19: 288-299.
Pederson, N., Jacoby, G.C., D'Arrigo, R.D., Cook, E.R. and Buckley, B.M. 2001. Hydrometeorological reconstructions for northeastern Mongolia derived from tree rings: 1651-1995. Journal of Climate 14: 872-881.
Pekarova, P., Miklanek, P. and Pekar, J. 2003. Spatial and temporal runoff oscillation analysis of the main rivers of the world during the 19th-20th centuries. Journal of Hydrology 274: 62-79.
Last updated 8 August 2007