Don Cheadle talks with a displaced meat-packing plant worker, Nelly Montez, about the punishing multi-year drought in Texas that drastically reduced the cattle herd in the first episode of Years of Living Dangerously, which aired April 13 and can be viewed online. A USDA spreadsheet on cattle losses, or a map of the most severe period during the recent drought in Texas, do not do justice in conveying the stories of people demonstrating courage in the face of mighty external forces. This episode has several surprising stories that I will not soon forget.
Don Cheadle and Nelly Montez in Plainview, Texas during filming of Years of Living Dangerously.
The lives disrupted, the questions people are asking, and the struggles confronted by the town of Plainview are a story that has implications far beyond Texas. To unpack this, Don Cheadle talks with Katharine Hayhoe, who eloquently combines her faith and science expertise to explain how our choices are in the mix of causes of the Texas drought.
Drawing upon her research into historic and future extreme heat risk to drought risk she connects the dots on the mechanisms: “As climate changes, warmer temperatures will make our droughts worse, on average, by increasing the amount of water that evaporates during the drought, and drying out the soil.”
Is the recent Texas drought unprecedented?
The recent multi-year drought in Texas had a period in October 2011 when nearly all counties in Texas were categorized as being in “exceptional drought” – the highest category – by the U.S. Drought Monitor. Indeed the March to August 2011 growing season in Texas was the hottest and driest on record.
Exceptional drought category for nearly all of Texas in the October 4, 2011 image from the animation of the U.S. Drought Monitor maps available here.
To study how exceptional this was, David Rupp and colleagues found that the risks of severe heat conditions in 2011 were 20 times more likely now in Texas compared to dry years in the 1960s. They also found an increased likelihood of severe drought. To understand what this means we can look at the research approach.
Natural cycles in the Pacific Ocean can bring hot and dry winter conditions (La Niña) or wet and cool winter conditions (El Niño) in the Texas region. Therefore the study compares the dry La Niña year of 2008 with dry La Niña years in the 1960s. This allowed Rupp and colleagues to assess any long-term shifts in risks that go beyond natural variability. Importantly, their study illustrates how natural variability and human-induced climate change can work in concert to create drought conditions.
To investigate such rare events, a huge number of simulations were run on a public volunteer network of computers. These simulations help create “recurrence interval” findings. They are similar to the 100-year flood event assessments for insurance. For example, a recurrence interval of five years means the probability of occurrence in any given year is one in five, or a 20 percent chance of occurrence in any given year.
I created this image based on Fig 9 in Rupp et al., 2012 BAMS. Modified photos from Gary Nored, Texas Parks and Wildlife (left) and Robert Burns – Texas AgriLife Extension Service (right).
Rupp and colleagues found that the recurrence interval in the growing season during dry La Niña years has changed since the 1960s. The same growing season heat event in 1964 that had a recurrence interval of 100 years, in 2008 would have had a recurrence interval of just five years.
Putting this all together, Rupp and colleagues state the risks of such an extreme 2011 temperature in Texas had increased over the last four to five decades. In controlling for natural variability, by comparing dry La Niña years separated by several decades, the leading suspect for a large contribution to this growing risk is excess heat-trapping gases from human activities.
The first episode of Years of Living Dangerously also tracks Harrison Ford as he tackles Palm Oil trends in Indonesia and Thomas Friedman looking into ingredients for unrest amid an epic drought displacing people in Syria.