Mean annual temperature has increased by approximately 1°F since the first half of the 20th century. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century, with associated increases in extreme heat events.
Although projected changes in annual precipitation are uncertain, increases in extreme precipitation events are projected. Higher temperatures will increase soil moisture loss during dry spells, increasing the intensity of naturally occurring droughts.
The number of landfalling hurricanes in Texas is highly variable from year to year. As the climate warms, increases in hurricane rainfall rates, storm surge height due to sea level rise, and the intensity of the strongest hurricanes are projected.
The Texas climate is characterized by hot summers and cool to mild winters. Three geographical features largely influence the state’s varied climate. The Rocky Mountains block intrusions of moist Pacific air from the west and tend to channel arctic air masses southward during the winter. The relatively flat central North American continent allows easy north and south movement of air masses. The Gulf of Mexico is the primary source of moisture, most readily available to the eastern part of the state. As a result of these factors, the state exhibits large east-west variations in precipitation and is subject to frequent occurrences of a variety of extreme events, including hurricanes, tornadoes, droughts, heat waves, cold waves, and intense precipitation. Increased demand for limited water supplies due to rapid population growth, especially in urban areas, may increase Texas’ vulnerability to naturally occurring droughts.
Mean annual temperatures has increased approximately 1°F since the first half of the 20th century (Figure 1). While there is no overall trend in extremely hot days (maximum temperature above 100°F) (Figure 2), the number of very warm nights (minimum temperature below 75°F) was a record high during the latest 2010–2014 period (Figure 3). This was due to very high values during the drought years of 2011 and 2012 when very warm nights were very frequent both along the coast (where they are a common feature of the climate due to warm waters) and in the interior (where they are less common). The urban heat island effect increased these occurrences in city centers. In 2011, Texas recorded its warmest summer on record (since 1895) and broke the record for the statewide-average highest number of days with temperatures of 100°F or more. The Dallas-Fort Worth area endured 40 consecutive days in excess of 100°F, which was the second longest streak on record (1898–2011). The record dry conditions contributed to the higher temperatures.
Daily minimum temperatures in January typically range from about 20°F in the northern Panhandle to about 50°F near the mouth of the Rio Grande River. The annual number of days of extreme cold (maximum temperatures below 32°F) was well above average in the 1970s and 1980s but since then has fluctuated near the long-term average (Figure 4a).
Average annual precipitation varies from less than 10 inches in the far west to greater than 50 inches in the far east. The driest multi-year periods were in the 1890s, 1950s, and 2000s, and the wettest in the 1940s and mid-1990s (Figure 4b). The driest 5-yr period was 1952–1956 and the wettest was 1990–1994. In the 1990s and early 2000s, the number of extreme precipitation events was well-above average, but the state has experienced below average rainfall and extreme precipitation events over the last five years (Figure 4c). However, this extended dry period was interrupted in May 2015 with a statewide monthly average rainfall total of 9.05 inches, breaking the previous all-time monthly record by well over two inches (Figure 5a). During one specific late-May episode, the Blanco River at Wimberly (south-central Texas) experienced historic flash and river flooding following a 1- to 2-day rainfall of 4–12 inches (Figure 5b), rising 35 feet in approximately 3 hours.
Texas is consistently ranked in the top 10 states affected by extreme events. In 2011, Texas was hit by eight of the nation’s billion dollar disasters. The three most impactful events were drought, extreme heat, and wildfires. The warmest and the driest summer in the historical record (Figure 6) helped fuel the worst wildfire season since statewide records began (approximately 1990), with nearly 4 million acres burned and $750 million in damages. Since the creation of the United States Drought Monitor Map in 2000, Texas has been completely drought-free for only approximately 8% of the time (2000–2014), and at least half of the state has been under drought conditions for approximately 42% of the time over the same period. Paleoclimatic records indicate that droughts of the severity of 2011 have occurred occasionally in the pat 1000 years (Figure 6). Higher temperatures in combination with drought conditions are likely to increase the severity, frequency, and extent of wildfires in the future posing significant harm to property, human health, and the livelihood of residents.
Over the period of 1900 to 2010, the Texas coastline endured more than 85 tropical storms and hurricanes (about 3 storms every 4 years), with approximately half of them hurricanes (Figure 4d). Since 2000, Texas has experienced 12 named storms, including 5 destructive hurricanes, with Hurricane Rita (Category 3) and Hurricane Ike (Category 2) causing the most significant damage. While Hurricane Rita holds the designation as causing the largest U.S. evacuation in history, Hurricane Ike is the costliest hurricane in Texas history, with an estimated $19.3 billion in damages. Along the southern coast, surges of between 11 and 13 feet typically have return periods of 25 years (Figure 7).
Over the past 30 years (1985–2014), Texas has averaged 140 tornadoes and 4 tornado fatalities per year. Events can occur all year, though activity typically peaks between April and June.
Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, average annual temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. Increases in the number of extremely hot days and decreases in the number of extremely cold days are projected to accompany the overall warming. By 2055, an estimated increase of 20–30 days over 95°F is projected under one pathway, with the greatest increase in southwestern Texas.
Future changes in annual average precipitation are uncertain (Figure 8), but an increase in intense rainfall is likely. Furthermore, even if average precipitation does not change, higher temperatures will increase the rate of soil moisture loss and thus naturally occurring droughts will likely be more intense. Longer dry spells are also projected.
Increased drought severity combined with increased human demand for surface water will cause changes in streamflow, with extended reductions of freshwater inflow to Texas bays and estuaries. Such reductions in streamflow will cause temporary or permanent changes to bay salinity and oxygen content, with potentially major impacts to bay and estuary ecosystems, such as negatively affecting organism growth, reproduction, and survival.
Future changes in the frequency and severity of tornadoes, hail, and severe thunderstorms are uncertain. However, hurricane intensity and rainfall are projected to increase for Texas as the climate warms.
Since 1880, global sea level has risen by about 8 inches. Along the Texas coastline, sea level rise has been measured between 5 and 17 inches per century, causing the loss of an average of 180 acres of coastline per year. Sea level is projected to rise another 1 to 4 feet by 2100 as a result of both past and future emissions from human activities (Figure 9). Sea level rise has caused an increase in tidal floods associated with nuisance-level impacts. Nuisance floods are events in which water levels exceed the local threshold (set by NOAA’s National Weather Service) for minor impacts. These events can damage infrastructure, cause road closures, and overwhelm storm drains. As sea level has risen along the Texas coastline, the number of tidal flood days has also increased, with the greatest number occurring in 2008 and 2015 (Figure 10). Future sea level rise will increase the frequency of nuisance flooding (Figure 9) and the potential for greater damage from storm surge.