What was done
In the words of the authors, "absolutely dated tree-ring-width chronologies from five sampling sites in west-central Mongolia [all of them "in or near the Selenge River basin, the largest river in Mongolia"] were used in precipitation models, and an individual model was made using the longest of the five tree-ring records (1340-2002)." Then, they developed "a reconstruction of streamflow that extends from 1637 to 1997." Of this latter reconstruction they say that "streamflow can be a better indicator of regional water resources than individual station precipitation records," because "streamflow integrates the areal effects of precipitation input and evapotranspiration losses," which "system of moisture balance is more similar to the hydrologic environment of trees than precipitation alone."

What was learned
On the ten driest five-year periods of the 360-year Selenge streamflow record, only one occurred during the 20th century (and that just barely:1901-1905, sixth driest of the ten extreme periods), while of the ten wettest five-year periods, only two occurred during the 20th century (1990-1994 and 1917-1921, the second and eighth wettest of the ten extreme periods, respectively). Consequently, as Davi et al. describe the situation, "there is much wider variation in the long-term tree-ring record than in the limited record of measured precipitation."

What it means
Climate alarmists claim that global warming leads to more frequent and more extreme periods of both wetness and dryness (floods and droughts). In the case of west-central Mongolia, however, just the opposite appears to be the case. Over the course of the 20th century, which climate alarmists describe as having experienced a warming that was unprecedented over the past two millennia, extremes of both dryness and wetness were both less frequent and less severe.