Climate model predictions of CO2-induced global warming typically suggest that rising temperatures should be accompanied by increases in rainfall amounts and intensities, as well as enhanced variability. As a result, many scientists are examining various historical and proxy precipitation records in an effort to determine how temperature changes of the past millennium may have impacted these aspects of earth's hydrologic cycle. In this summary, we review what several such studies have learned about precipitation in Asia.
Kripalani et al. (2003) note that globally-averaged temperatures are projected to rise under all scenarios of future energy use, according to the IPCC, leading to "increased variability and strength of the Asian monsoon." Consequently, to see if there is any sign of such a precipitation response in real-world measurements, they examined Indian monsoon rainfall using observational data for the period 1871-2001 that were obtained from 306 stations distributed across the country. In doing so, they discovered decadal variations running throughout the record that reveal "distinct alternate epochs of above and below normal rainfall," which epochs "tend to last for about three decades." In addition, they report "there is no clear evidence to suggest that the strength and variability of the Indian Monsoon Rainfall (IMR) nor the epochal changes are affected by the global warming." They also report that "studies by several authors in India have shown that there is no statistically significant trend in IMR for the country as a whole." Last of all, they report that "Singh (2001) investigated the long term trends in the frequency of cyclonic disturbances over the Bay of Bengal and the Arabian Sea using 100-year (1890-1999) data and found significant decreasing trends [our italics]." As a result, Kripalani et al. conclude that "there seem[s] to be no support for the intensification of the monsoon nor any support for the increased hydrological cycle as hypothesized by [the] greenhouse warming scenario in model simulations." In addition, they say that "the analysis of observed data for the 131-year period (1871-2001) suggests no clear role of global warming in the variability of monsoon rainfall over India," much as Kripalani and Kulkarni (2001) had concluded two years earlier. Hence, it is doubly clear that the climate models appear to have struck out with respect to both of their Asian monsoon-related projections.
Kanae et al. (2004) also note that both the number and intensity of heavy precipitation events are projected to increase in a warming world, according to the IPCC. Hence, they investigate this climate-model-derived hypothesis with digitalized hourly precipitation data recorded at the Tokyo Observatory of the Japan Meteorological Agency for the period 1890-1999. Within this context, they report that "many hourly heavy precipitation events (above 20 mm/hour) occurred in the 1990s compared with the 1970s and the 1980s," and that against that backdrop, "the 1990s seems to be unprecedented." However, they note that "hourly heavy precipitation around the 1940s is even stronger/more frequent than in the 1990s." In fact, their plots of maximum hourly precipitation and the number of extreme hourly precipitation events rise fairly regularly from the 1890s to peak in the 1940s, after which declines set in that bottom out in the 1970s and then reverse to rise to endpoints in the 1990s that are not yet as high as the peaks of the 1940s.
Taking a somewhat longer view of the subject, Pederson et al. (2001) used tree-ring chronologies from northeastern Mongolia to reconstruct annual precipitation and streamflow histories for the period 1651-1995. Analyses of both standard deviations and five-year intervals of extreme wet and dry periods of this record revealed that "variations over the recent period of instrumental data are not unusual relative to the prior record." The authors do state, however, that the reconstructions "appear to show more frequent extended wet periods in more recent decades," but they say this observation "does not demonstrate unequivocal evidence of an increase in precipitation as suggested by some climate models." In addition, they report that spectral analysis of the data revealed significant periodicities around 12 and 20-24 years, suggesting, in their words, "possible evidence for solar influences in these reconstructions for northeastern Mongolia."
Going back even further in time, Touchan et al. (2003) developed two reconstructions of spring (May-June) precipitation for southwestern Turkey from tree-ring width measurements, one of which extended from 1776 to 1998 and one from 1339 to 1998. These reconstructions, in their words, "show clear evidence of multi-year to decadal variations in spring precipitation," but they report that "dry periods of 1-2 years were well distributed throughout the record" and that the same was true of wet periods of 1-2 years' duration. With respect to more extreme events, however, the period that preceded the Industrial Revolution stood out. They say, for example, that "all of the wettest 5-year periods occurred prior to 1756," while the longest period of reconstructed spring drought was the four-year period 1476-79, and the single driest spring was 1746. Hence, it is clear that Turkey's greatest precipitation extremes occurred prior to the Modern Warm Period, which is just the opposite of what climate alarmists typically claim about extreme weather and its response to global warming.
Looking much further back in time (from 9600 to 6100 years ago) were Neff et al. (2001), who explored the relationship between a 14C tree-ring record and a δ18O proxy record of monsoon rainfall intensity as recorded in calcite δ18O data obtained from a stalagmite in northern Oman. They found that the correlation between the two data sets was "extremely strong," and that a spectral analysis of the data revealed statistically significant periodicities centered on 779, 205, 134 and 87 years for the δ18O record and periodicities of 206, 148, 126, 89, 26 and 10.4 years for the 14C record. Consequently, because variations in 14C tree-ring records are generally attributed to variations in solar activity, and because of the 14C record's strong correlation with the δ18O record, as well as the closely corresponding results of their spectral analyses, Neff et al. conclude there is "solid evidence" that both signals are responding to solar forcing.
In conclusion, the evidence reviewed here provides absolutely no support for the point of view promulgated by the world's climate alarmists, i.e., that precipitation in a warming world becomes more variable and intense. In fact, in some cases it tends to suggest just the opposite, and provides support for the proposition that precipitation responds more to cyclical variations in solar activity than to anything else.
References
Kanae, S., Oki, T. and Kashida, A. 2004. Changes in hourly heavy precipitation at Tokyo from 1890 to 1999. Journal of the Meteorological Society of Japan 82: 241-247.
Kripalani, R.H. and Kulkarni, A. 2001. Monsoon rainfall variations and teleconnections over south and east Asia. International Journal of Climatology 21: 603-616.
Kripalani, R.H., Kulkarni, A., Sabade, S.S. and Khandekar, M.L. 2003. Indian monsoon variability in a global warming scenario. Natural Hazards 29: 189-206.
Neff, U., Burns, S.J., Mangini, A., Mudelsee, M., Fleitmann, D and Matter, A. 2001. Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago. Nature 411: 290-293.
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.
Singh, O.P. 2001. Long term trends in the frequency of monsoonal cyclonic disturbances over the north Indian ocean. Mausam 52: 655-658.
Touchan, R., Garfin, G.M., Meko, D.M., Funkhouser, G., Erkan, N., Hughes, M.K. and Wallin, B.S. 2003. Preliminary reconstructions of spring precipitation in southwestern Turkey from tree-ring width. International Journal of Climatology 23: 157-171.