Background
Climate alarmists contend that global warming should lead to both more frequent and more extreme weather phenomena, such as droughts and floods. Hence, it is important to search for real-world evidence of these phenomena, which is precisely what Marengo does in this data-based study of the hydrological history of the Amazon Basin of South America.

What was done
Morengo worked with hydrometeorological indices for the Amazon basin and its several sub-basins in an effort designed "to explore long-term variability of climate since the late 1920s and the presence of trends and/or cycles in rainfall and river indices in the basin," which analyses were based on northern and southern Amazonian rainfall data that were originally developed by Marengo (1992) and Marengo and Hastenrath (1993), and which were subsequently updated by Marengo (2004).

What was learned
The Brazilian researcher reports that "no systematic unidirectional long-term trends towards drier or wetter conditions have been identified since the 1920s." Instead, he found that "the rainfall and river series show variability at inter-annual scales."

What it means
With respect to the patterns he uncovered, Morengo writes that they are "characteristic of decadal and multi-decadal modes," which he describes as "indicators of natural climate variability" that are linked to the El Niņo Southern Oscillation, "rather than any unidirectional trend towards drier conditions (as one would expect, due to increased deforestation or to global warming)." Hence, in response to what climate alarmists call the unprecedented warming of the 20th century, there appears to have been a total lack of what they predicted should have occurred - in terms of hydrology - in response to this "catastrophic" phenomenon.

References
Marengo, J.A. 1992. Interannual variability of surface climate in the Amazon basin. International Journal of Climatology 12: 853-863.

Marengo, J.A. 2004. Interdecadal and long term rainfall variability in the Amazon basin. Theoretical and Applied Climatology 78: 79-96.

Marengo, J. and Hastenrath, S. 1993. Case studies of extreme climatic events in the Amazon basin. Journal of Climate 6: 617-627.