Drought: A Paleo Perspective
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A Final Word

How is the paleoclimatic record of drought relevant for understanding or predicting drought today, or in the future?
The North American record of past drought allows us to determine what has been the range of natural variability of drought over hundreds if not thousands of years. This long-term perspective is important because although severe droughts have occurred in the 20th century, a more long-term look at past droughts, when climate conditions appear to have been similar to today, indicates that 20th century droughts do not represent the possible range of drought variability.

The paleoclimatic record of past droughts is a better guide than what is provided by the instrumental record alone of what we should expect in terms of the magnitude and duration of future droughts. For example, paleoclimatic data suggest that droughts as severe at the 1950s drought have occurred in central North America several times a century over the past 300-400 years, and thus we should expect (and plan for) similar droughts in the future. The paleoclimatic record also indicates that droughts of a much greater duration than any in 20th century have occurred in parts of North American as recently as 500 years ago. These data indicate that we should be aware of the possibility of such droughts occurring in the future as well. The occurrence of such sustained drought conditions today would be a natural disaster of a magnitude unprecedented in the 20th century.

In addition to establishing a baseline of drought variability over the long term, the paleoclimatic record of drought provides information about drought under a range of naturally varying climate conditions, some of which are the same as the climate of today and some which are quite different. This paleoclimatic perspective can be used to learn about the underlying process and characteristics of drought under very different future climate conditions.

The impact of droughts over the last few decades have shown that some regions and sectors of the population are becoming increasingly vulnerable to drought. Compounding these vulnerabilities is the uncertainty of the effects of human activities and global warming on climate in general and on drought in particular. A number of climate model simulations for doubled CO2 conditions suggest an increased frequency of drought in midcontinental regions (e.g. Gregory et al, 1997 , Mearns et al, 2000) whereas other model simulations and recent decadal trends in the instrumental record suggest wetter conditions, at least in the short term, due to an intensification of the hydrologic cycle associated with warmer sea surface temperatures. Better constrained answers to the question of the severity of future droughts requires improved understanding and modeling of the processes underlying the drought behavior exhibited in both the instrumental and the paleoclimate records.

What can we do to better understand past droughts and predict future droughts?
Our understanding of what causes drought conditions to persist for years and decades is far from complete. Much work is needed to comprehensively understand drought and the causes of drought, and to improve drought prediction capabilities. Putting together the pieces of past droughts through the use of paleoclimatic data is a vital part of building this understanding and developing an improved capacity to anticipate droughts in the future.

Focused efforts are needed to bring together paleoclimatic records of past droughts with scientists working to better understand the workings of the climate system. Currently, scientists are working on this sort of focused effort for western Canada. In the Prarie Drought Paleolimnology Project, paleoecological reconstructions will be incorporated into novel models specifically developed for use with long-term climatic data. The models will be used to predict drought frequency, duration and intensity over the next 5-50 years. More such efforts are needed to understand the drought across all of North America.