Paper No. 2
Presentation Time: 8:35 AM
DROUGHTS OF THE PAST, ANALOGUES FOR THE FUTURE?
Paleoclimatic data provide evidence for widespread and severe droughts against which events of the 20th and 21st centuries can be assessed. In the western US, there are numerous droughts documented in paleoclimatic records over the past 500-2000 years that have been more severe and sustained than those occurring during the modern period. There is no reason to believe that droughts with similar moisture deficits could not occur in the future, but are the droughts of the past a useful analogue for what might be expected in the future, given warming temperature? The most valuable analogues for future droughts are those that occurred under warmer temperatures, such as during the medieval period, approximately 900-1300 AD. Reconstructions of past drought, based on a continental network of tree-ring data and supported by other paleoclimatic data, indicate the spatial extent of drought over the medieval period was more extensive than any time since that period. Individual tree-ring based reconstructions show the regional expression of this period of drought. For example, in the upper Colorado River basin, the most sustained period of drought over the past 1200 years was centered on 1150, and spanned six decades with only a handful of above average flows. Similar conditions occurred in the Sacramento River basin. However, current warming temperatures suggest that medieval droughts, were they to occur in the future, would take place under even warmer temperatures. The impacts of recent warming, combined with region drought, are evident in paleoclimatic data from the Rocky Mountains, and indicate elevated temperatures may synchronize decreases in snowpack across the entire region. Droughts are one of the most costly and disruptive extreme climate events that impact society today, and paleoclimatic data provide some guidance for the magnitude of droughts that can be expected in the future. However, these extreme events and their impacts will be further exacerbated by anthropogenic warming.