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Drought Happens

Written by David Hoover, SoGES 2013-2014 Sustainability Leadership Fellow, and PhD Candidate in the Department of Biology and Graduate Degree Program in Ecology

Droughts are one of the most expensive extreme weather events, second only to hurricanes. In 2012, the US experienced its most extensive drought since the 1930’s Dust Bowl. Over half the country experienced moderate to extreme drought, costing an estimated $30 billion. The central plains were hit the hardest, causing widespread failure of crops and leading to the lowest cattle heard size since 1951, which has recently driven beef costs to the highest level since 1987.

The newest IPCC report on climate change predicts that extreme events, such as drought, will be more frequent and intense in the future as result of manmade climate change. 

This leads to the question: Was the 2012 US drought caused by climate change?

Well, most climate scientists would argue that currently we cannot attribute individual weather events to climate change. However, it is very likely that today’s droughts are influenced by climate change. For example, warmer air temperatures can increase the evaporative demand of the atmosphere and thus intensify the effects of drought. Warmer temperatures can also alter hydrologic cycles, changing rainfall patterns and amounts. Combined, these two factors – greater evaporation and altered precipitation – can affect drought severity.  

But as bad as the 2012 US drought was, natural climate variability over the past millennia have spawned droughts worse than anything we have witnessed or are prepared to deal with as a society.

We can categorize drought severity on three different time scales – yearlong (think 2012 US drought), multiyear (think 1930’s Dust Bowl) and multidecade (think “megadrought”). A recent study by Cook et al. (2014), examined tree ring data in North America for the past 1000 years, to investigate drought variability over time scales longer than our instrumental record. It turns out that the 2012 US drought was not an uncommon event – short-term pancontinental droughts occurred about 12% of the time or about once every decade. On the other hand, there were only four megadroughts during this period, all occurring during the Medieval Warming Period (between 1900-1400 AD), and each lasting for decades.

So perhaps a better question is: What if the 2012 drought had developed into a megadrought?

The truth is we have no idea what the consequences of such an event would be. We can look back at the 1930’s Dust Bowl, but that was just under a decade long (not a megadrought) and the ecological and agricultural impacts were exacerbated by poor agricultural practices. Basically the Dust Bowl looks pretty tame when we zoom our timescale out to the millennial level.

Our current thinking about drought is small, or more accurately, short. Our agricultural systems struggle with single year droughts and few ecological studies examine drought effects beyond a single grant funding cycle (about four years). Although environmentally and economically disruptive, most ecosystems and our highly industrialized agricultural system have the resilience to bounce back from such short-term droughts. However the impacts of megadroughts are uncertain at best and apocalyptic at worst (ask the Mayans). Therefore it is important that we begin to consider how to improve societal resilience and investigate the potential ecological consequences of megadroughts.

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