As far as drought is concerned, for the next 20 to 30 years, State Climatologist Dr. John Nielsen-Gammon, College Station, said he is optimistic.
“And then I turn seriously pessimistic,” he said.
While reports from Texas A&M AgriLife Extension Service personnel show an improvement in rainfall during the last six months, Nielsen-Gammon said rainfall patterns are only one of the major factors in drought.
The other factor is evaporation from increased temperature, he said. Global warming has meant an average temperature increase in Texas of about 1.5 degrees since the 1970s. While this may not seem like much of an increase to most people, it’s enough to increase the evapotranspiration of plants and loss of surface water by several percent.
“Any incremental increase of severity of the drought starts having a huge impact,” Nielsen-Gammon said. “It doesn’t matter at all during normal conditions, but when you’re in an extreme drought, it can make the difference between making it through the drought and not making it through.”
Despite the rising temperatures, Nielsen-Gammon remained optimistic for agriculture during the next couple of decades because of an expected increase in rainfall compared to the last 10 or 15 years, he said.
“Over the long-term, yes, there will be a trend to greater evaporation,” he said. “But then there are also short-term trends on top of that long-term trend. Based on how the Atlantic and Pacific Oceans operate, and how they influence our weather, over the next 20 to 25 years, we are probably going to see an improvement in drought conditions, mainly from an increase in rainfall amounts. This is because the two oceans have been working against us for the past decade or decade and half, and that trend tends to flip back and forth every 20 years or so.”
Nielsen-Gammon noted there is another side effect of global warming that rules in favor of crop production. Plants open up stomata to take in carbon dioxide, their basic building material, and to cool themselves by evapotranspiration. As atmospheric carbon dioxide levels rise, their pores don’t need to open as much to get the carbon dioxide they need. As a result, they lose less water through transpiration and tend to become more drought-tolerant. When there is ample water, the plants can grow faster, though that growth may be limited by things such as nutrient availability.
In addition to his duties as state climatologist and professor of meteorology at Texas A&M University, Nielsen-Gammon also contributes to a blog on global warming at http://climatechangenationalforum.org.