- What were the biggest changes or surprises that the researchers want to make sure Texans know?
All Texans – including our state’s policymakers – should understand the significant challenges our people and economy will face as extreme weather trends continue through 2036. Texas will be hotter, more susceptible to severe drought, and more vulnerable to intense weather events and urban flooding.
This report can help the state incorporate these climatic considerations into plans to build, strengthen and pay for critical infrastructure around water and flood control, energy, transportation, and even public education.
- How did you approach this study? What is the relationship between historic trends and future weather patterns?
The report’s conclusions were drawn through observations and analyses of historical meteorological and climate data for Texas. It’s hard to argue with historical data because historic weather actually happened. That being said, some data are more reliable than others (i.e., we didn’t go out and chase tornadoes in the 1950s, so we really don’t know much about tornado trends).
Historic climate trends are indicative of future trends if the physical mechanisms that cause them are clearly related to long-term global climate changes. For example, temperatures are increasing not just in Texas, but everywhere, and we know why. Precipitation is more variable, and climate models aren’t all on the same page. Therefore, it’s not clear whether Texas’s historical trend toward increasing precipitation totals will continue. Precipitation intensity, though, has a more direct physical relationship to temperatures, and observations and models both show intensity increases.
- How does this Texas-focused analysis compare to other research regarding the warming of the planet?
The report relies on lots of other studies, some Texas-focused and others broader in scope. It turns out that what’s happening in Texas is not much different from what’s happening elsewhere, especially in places with similar climates. Texas is a special place in a lot of ways, but its climate trends are actually nothing special. Temperatures, for example, have risen just a little bit more than the global average since 1975.
- This summer in Texas was cooler and wetter than other summers – can you put this into context with these long-term trends showing a warming climate?
Summertime temperatures in Texas are closely tied to rainfall. If we have a wet spring and early summer, we’re not going to tend to reach sustained high temperatures. What we’ve seen, though, is that hot summers are getting warmer, and cool summers are getting warmer, too. While this summer seemed quite mild to us in the context of our recent climate, if you go back far enough, you’ll find about fifty other summers in the past 125 years or so with lower temperature peaks.
The other thing a wet spring and early summer brings is humidity. This summer, nighttime lows were not all that low. The coldest temperatures observed this summer were a couple of degrees warmer than the historical average. It’s a matter of taste whether you’d rather have cool days and warm nights, or warmer days and cool nights, but they’re both getting warmer.
- Would you put into context what damage Texans should expect for every degree increase in temperature?
Nothing special happens when the temperature on a given day goes up by a degree (or three). At first, you don’t notice anything different. But occasionally, something happens, and you think, “Gee, that never used to happen before,” or “Again? This is happening again already?”
Imagine you are visiting a place where bets are made, and you are making a few hundred $1 bets. The last time you were there, the odds favored the house by 1%. This time, they favor the house by 2%. You win about half your bets either way, but if you play for long enough, you realize you’re losing more money than you used to. That’s how you notice climate change’s effect on average temperatures: not because a particular day is warm, but because the warm days add up more than they used to.
Now, suppose you’re playing a different game. You must bet your entire life savings each time, and if you win, you win $1. The odds are set up so that you’ll win almost every time, but still, it’s a rather uncomfortable game to play. Then they change the odds so that the chances of losing your life savings doubles. Would you now expect to lose your life savings? No, not with a single bet. But if you play enough times, you might lose your life savings sooner, or more frequently, or maybe not at all if you’re lucky. What happens is up to chance, but your risk has gone way up. That’s how climate change affects many types of weather catastrophes.
Texas is a large state, so we’re going to get our share of catastrophes. If you add up the costs of various storms, Texans should anticipate billions of additional dollars in damages driven by extreme weather — unless the state takes action to create a more resilient infrastructure. Examples include:
The cost of Winter Storm Uri: https://www.texastribune.org/2021/02/25/texas-winter-storm-cost-budget/
The cost of Hurricane Harvey: https://www.lamar.edu/_files/documents/resilience-recovery/grant/recovery-and-resiliency/hurric2.pdf
The cost of drought: https://comptroller.texas.gov/economy/fiscal-notes/2019/apr/tx-water-planning.php
- Based on this research, should we expect another Winter Storm Uri?
The data indicate that such storms are likely to decrease in frequency, but they remain a threat. Texas has experienced very few extreme statewide snowstorms like the one that hit in February 2021. Given the size of Texas and the typical scale of snowstorms at this latitude, it is rare for individual snowstorms to affect most of the state simultaneously. The low temperatures were very unusual, but generally, they were not unprecedented either.
Both the snow and the cold should gradually become less likely over time. Over the next fifteen years, the odds will be just a little bit lower than they were going into 2021. That’s nice, but extreme weather like Uri could certainly happen again.
- What about changes to the polar vortex? Won’t it make these storms more likely, rather than less likely?
There has been some research in recent years suggesting that changes in snowfall patterns and Arctic sea ice cover will increase chances of disruption of the stratospheric polar vortex and the jet stream. That will increase the odds of triggering a chain reaction of events that can lead a storm like Uri.
However, winter temperatures are getting warmer, and Arctic temperatures are getting warmer rather quickly. That makes extremely cold weather and snowstorms in Texas less likely. Future Uris will tend to be milder, and more of them will produce cold rain rather than snow. Essentially, the trend toward milder winter temperatures will have a stronger impact on our chances of extreme winter weather than the trend toward a more disrupted stratospheric vortex. Indeed, it already has – extreme winter temperatures in Texas have gotten warmer.
- Four years ago, Hurricane Harvey caused $125 billion in damage, according to the National Hurricane Center. What can we expect regarding future hurricanes?
In general, major hurricanes have become more common, rapid intensification has become more common, intense rain from hurricanes has become heavier, and the sea level has risen, which makes storm surges higher. It’s not clear whether the total number of major hurricanes will continue to increase, but it’s very likely that the fraction of storms that become major will increase. The increased intensity of rainfall from hurricanes is a robust trend, and sea level rise is certainly not stopping anytime soon. So, of the three major types of damage from hurricanes — storm surge, freshwater flooding, and wind damage — at least two out of three are likely to get worse.
On the bright side, recent research out of Rice University suggests that hurricanes might become less likely to stall over Texas. But as Hurricane Ida showed Louisiana this past September, fast-moving storms can still be quite disruptive.
- How is it that Texas will face more extreme drought over the next 15 years, given it appears we will be both wetter and drier?
We’ll be wetter in the sense that extreme rainfall is likely to become more extreme. Overall rainfall might increase too, but probably not by much. So if rainfall is more likely to be extreme, and overall rainfall doesn’t change very much, that means that rainfall will in general become more erratic, with larger gaps between the heavier rains. That’s a good way to trigger a drought.
Meanwhile, warmer temperatures lead to more rapid evaporation of the water that soaks into the soil or runs off into reservoirs. When rainfall is below normal for a few months, everything will dry out faster, and drought impacts (such as declines in drinking water availability) will happen sooner. In general, it seems that droughts will become more extreme.
How much more extreme depends on the particular drought impact being considered. Crops will respond differently to the contributing factors than will surface water supplies, and groundwater supplies are different yet again. At this point, it’s not possible to put a number on how large the change in drought severity will be. Also, these trends are trends in contributing factors. Good, old-fashioned rainfall matters too, and Texas can have entire decades with rain well above normal or rain well below normal. So, while an underlying drying trend is there, there’s no way to know the specifics of how it will play out.
- When we think of extreme rainfall in Texas, many people automatically think of the Houston area, given the impact of Hurricane Harvey four years ago. Can you talk about what your data shows?
The Houston metropolitan region stands out as a hotspot for increasing urban flooding trends; Harris County has more than 60% of the flood gauges that show increasing flood trends. Also, there’s a tendency for extreme rainfall to be increasing throughout Texas, and urban flooding is directly tied to extreme rainfall. So, you might think that Houstonians should be especially worried about further increases in flood risk.
But, it’s actually the opposite. Because Houston has seen so much urban flooding recently, they’re probably well aware of the problem. They’ve had more than their share of flooding: through 2036, the odds of more extreme rainfall in Houston are probably less than what recent experience suggests. Instead, it’s most of the other cities in Texas that should be worried. They’ve been lucky, with not a lot of floods recently, despite an ever-increasing risk. Sooner or later, the actual weather is going to catch up with the odds there, and extreme rain-producing storms are going to be mostly hitting places other than southeast Texas. The combination of changing luck and worsening odds may catch a lot of people by surprise.
- Based on the map in this report, it appears that no corner of the state is immune to severe thunderstorms. Can you talk about what your research showed?
We can’t say much about severe thunderstorm trends, but it’s still helpful for people to better understand their risk, even if we don’t know how that risk is changing. Generally speaking, severe thunderstorms are more likely the farther north you go in Texas. The observations show large clusters of severe thunderstorm reports around major metropolitan areas, but that seems to be just because there are more people to see them and more things for them to damage. The same tendency applies to tornadoes and hail: the National Weather Service won’t get a report of building damage if there aren’t any buildings nearby.
- One of the findings of the report discusses hail in Texas. Can you talk about what your data shows about hail and how what we can expect?
On April 28th, 2021, a severe thunderstorm traveled down the HWY 90 corridor west of San Antonio, showering the region with damaging hail. Afterwards, someone found a giant 6.4″ hailstone near Hondo, TX. This was officially accepted as the largest well-documented hailstone ever in Texas.
Every year brings a risk of big hail. Warmer temperatures might mean less hail overall, particularly during the summer. But climate change will also increase the energy in thunderstorms, making it easier for hailstones to stay aloft and grow. With the studies we’ve seen so far, it seems that the main effect of climate change on hail might be to make big hail-producing storms more common earlier in springtime.
- Does the research determine whether Texas can expect more tornados?
No, it’s too hard to tell. There’s a good bit of research going on at the moment, but about the best we can say right now is that it looks like there will be more days apparently capable of helping tornadic supercells form.
- What happens after 2036?
The extreme weather trends continue. It seems clear that global temperatures are going to stay on an upward trajectory for several decades. Whatever is done to change greenhouse gas emissions is unlikely to have a substantial effect on global climate until after 2050. And as global climate changes, Texas climate follows. Since the report’s projections generally stop in 2036, they underestimate the overall potential impact of future climate change on Texas.
That’s “potential impact,” because the actual impact depends not just on future weather and climate, but on what Texas does to become more resilient to future weather and climate. Climate scientists can make projections of future climate, but climate scientists don’t have any special ability to make projections of what Texans will decide to do about it.