Beyond the next few years, climate change must be taken into account. Projected changes
in precipitation are relatively small compared to past natural precipitation variations
(Nielsen-Gammon, 2011), so it seems unlikely that anthropogenic climate change will
induce a substantial decrease in Texas precipitation by mid-century. Natural variations
presently have Texas in a dry phase, so it seems relatively likely that as the PDO and AMO
evolve over the next couple of decades Texas will pass into another relatively wet phase,
albeit temporary. Scientists also do not know whether La Niña, which exerts such a strong
influence on Texas weather from year to year, will become more or less frequent as the
climate changes.
Projected temperature changes are much larger than past decade-scale temperature
variations in Texas, and the projected warming is robust across models. While it is not
known how much warmer temperatures will become, an increase of several degrees
Fahrenheit by mid-century in Texas is well within the realm of possibility.
Whether such a large temperature increase comes to pass or not, it seems very likely that
temperatures will become at least somewhat warmer than present, so that evaporation will
have an increasingly large impact on water supplies throughout Texas. 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
