According to the Drought Monitor, drought conditions improved recently across some of the US. As of Jul. 9, 2013, 47.3% of the contiguous US is experiencing moderate or worse drought (D1-D4), as the early 2010s drought continues month after month. That is the lowest percentage in a number of months. The percentage area experiencing extreme to exceptional drought increased from 14.6% to 14.8%, but this is ~4% lower than it was six months ago. The eastern third of the US was wetter than normal during June, which helped keep drought at bay. The east coast in particular was much wetter than normal. Instead of Exceptional drought in Georgia and Extreme drought in Florida two years ago, there is flash flooding and rare dam water releases in the southeast. Eight eastern states experienced their top-three wettest Junes on record. The West is quite a different story. Long-term drought continues to exert its hold over the region, as it remains warmer and drier than normal month after month.
Figure 1 – US Drought Monitor map of drought conditions as of July 9th.
If we focus in on the West, we can see recent shifts in drought categories:
Figure 2 – US Drought Monitor map of drought conditions in Western US as of July 9th.
Early year snowmelt relief was short-lived, as drought conditions expanded as worsened in the past three months. More than three-fourths of the West is in Moderate drought. More than half of the West is now is Severe drought. And one-fifth of the West is in Extreme drought.
Temporary drought relief might occur in New Mexico and southern Colorado due to the recent heavy rains brought by a retrograding low pressure system that also brought cooler than normal temperatures to Oklahoma and Texas.
Here are the conditions for Colorado:
Figure 3 – US Drought Monitor map of drought conditions in Colorado as of July 9th.
There is some evidence of relief evident over the past six months here. Severe drought area dropped from 95-100% to 83%. Extreme drought area dropped significantly from 53% to 39%. Exceptional drought shifted in space from central Colorado to southeastern Colorado, which left the percentage area near 17%. The good news for southeastern Colorado is the recent delivery of substantial precipitation. It isn’t likely to alleviate the long-term drought, but will hopefully dent short-term drought.
US drought conditions are more influenced by Pacific and Atlantic sea surface temperature conditions than the global warming observed to date. Different natural oscillation phases preferentially condition environments for drought. Droughts in the West tend to occur during the cool phases of the Interdecadal Pacific Oscillation and the El Niño-Southern Oscillation, for instance. Beyond that, drought controls remain a significant unknown. Population growth in the West in the 21st century means scientists and policymakers need to better understand what conditions are likeliest to generate multidecadal droughts, as have occurred in the past.
As drought affects regions differentially, our policy responses vary. A growing number of water utilities recognize the need for a proactive mindset with respect to drought impacts. The last thing they want is their reliability to suffer. Americans are privileged in that clean, fresh water flows every time they turn on their tap. Crops continue to show up at their local stores despite terrible conditions in many areas of their own nation (albeit at a higher price, as found this year). Power utilities continue to provide hydroelectric-generated energy.
That last point will change in a warming and drying future. Regulations that limit the temperature of water discharged by power plants exist. Generally warmer climate conditions include warmer river and lake water today than what existed 30 years ago. Warmer water going into a plant either means warmer water out or a longer time spent in the plant, which reduces the amount of energy the plant can produce. Alternatively, we can continue to generate the same amount of power if we are willing to sacrifice ecosystems which depend on a very narrow range of water temperatures. As with other facets of climate change, technological innovation can help increase plant efficiency. I think innovation remains our best hope to minimize the number and magnitude of climate change impacts on human and ecological systems.