Among the long list of billion dollar weather-related disasters during 2011, there is one event that is still ongoing, its economic ramifications escalating with each passing day. The Texas drought - already the Lone Star State’s worst one-year drought on record - is now expected to last through at least next summer, and perhaps far longer than that, according to the latest climate projections released by NOAA’s Climate Prediction Center (CPC) and recent testimony by the Texas state climatologist.
In fact, CPC’s updated winter outlook, released last week, shows the potential for drought conditions to expand eastward along the Gulf Coast between December and February, extending down into Florida. The main reasoning behind this dry forecast is the likelihood that La Nina conditions will continue to be present in the tropical Pacific Ocean during much of the winter. La Nina, which is characterized by cooler-than-average ocean temperatures in the equatorial Pacific, tends to alter weather patterns in a way that favors drier-than-average conditions in Texas and parts of the Southeast, among other areas.
John Nielsen-Gammon, the Texas state climatologist, has posted a briefing on the drought that he gave to the Texas state Senate last month. It contains a wealth of statistics that help put this drought, and the dismal drought forecast, into historical context.
For example, did you know that the drought’s onset could be traced to a particular day? According to Nielsen-Gammon, the drought essentially began on Sept. 27, 2010, when a storm system departed Texas and seemingly took all the available moisture with it. This storm was followed by a year of much-below-normal precipitation.
Nielson-Gammon’s analysis delves into the question that is on the minds of most drought-weary Texans: when will the drought finally end?
“Because of the return of La Niña conditions in the tropical Pacific, a second year of drought in Texas is likely, which will result in continued drawdown of water supplies,” Nielson-Gammon writes. He continues:
Whether the drought will end after two years or last three years or beyond is impossible to predict with any certainty, but what is known is that Texas is in a period of enhanced drought susceptibility due to global ocean temperature patterns and has been since at least the year 2000. The good news is that these global patterns tend to reverse themselves over time, probably leading to an extended period of wetter weather for Texas, though this may not happen for another three to fifteen years. Looking into the distant future, the safest bet is that global temperatures will continue to increase, causing Texas droughts to be warmer and more strongly affected by evaporation.
On a conference call with reporters last week, top CPC climate forecasters said that some parts of Texas need 15 inches of rain or more in one month in order to break out of the drought, and this is unlikely to happen in the near future. The official U.S. Seasonal Drought Outlook shades the entire state of Texas in the dreaded deep brown color, denoting the expected “persistence” of drought conditions through the end of February (at least).
Substantial rains are always possible from May through October, so many parts of the state may well get lucky and receive significant drought relief by this time next year. However, there is no reason at this point to expect the summertime precipitation to be above normal, and even near-normal conditions would allow a continuation of the present drought into fall 2012. It therefore seems likely that at least a large portion of Texas will need to endure a second summer of drought.
Nielson-Gammon notes that it’s unlikely that the second year of drought will be as severe as the first one, simply because 2010-11 was so extraordinarily dry. “However, a continuation of the drought would be bad for water supplies across the state. The effects of drought tend to be cumulative on surface water storage and aquifers: continued depletion without adequate recharge would lead to more water restrictions and priority calls,” he writes.
The presentation Nielson-Gammon gave to the Texas legislature contains many sobering climate adaptation messages. For example, there’s this prudent warning: “While most water systems are designed for the drought of record, most have never actually had their infrastructure and water plans tested by the drought of record. It is not too late to consider the possibility that this drought may turn out to be worse than the drought of record and to take steps to prepare for that possibility.”
There’s also this heads up about how global warming may alter droughts in the coming years:
Future droughts will almost certainly be warmer than the Texas droughts of the past, and consequently will tend to be more severe even if precipitation is unchanged. It took rainfall only a third of normal to achieve summertime Texas temperatures five degrees warmer than their 20th century average; perhaps by mid-century a drought with two-thirds of normal precipitation will be sufficient to achieve similarly warm conditions.