sign in sign up
<<
Home , Climate of Texas

Chapter 5 Climate of

Climate of Texas 129 Chapter 5 Climate of Texas

From the hot, dry desert of Far and The average annual maximum daily temperature in the blue northers that blast the the state generally increases from about 70°F in to the humid, rainy pine forests of and the northern Panhandle to about 82°F in the the hurricanes that sweep across the Gulf Coast, Lower Valley, with the exception Texas’ climate is as varied as its landscape. That of mountainous areas in Far West Texas. variability is a result of the interactions between Texas’ unique geographic location and the move- Average annual ranges from over ments of seasonal air masses, such as arctic 55 inches in Beaumont to less than 10 inches in fronts, the jet stream, subtropical west winds, El Paso. Average annual gross lake surface evaporation tropical storms, and a subtropical high pressure ranges from less than 45 inches in East Texas system known as the Bermuda High (Figure 5.1). to more than 90 inches in Far West Texas. The is a dominant geographical feature, moderating temperatures along the Gulf Except for the wetter, eastern portion of the state, Coast and, more important, providing the ma- evaporation exceeds precipitation for most of Texas, jor source of moisture for the state (Carr, 1967; yielding a semiarid climate that becomes arid in Larkin and Bomar, 1983). The eastern Pacific Far West Texas. Ocean and land-recycled moisture also provide, to a lesser extent, a source for annual rainfall to The Gulf of Mexico is a dominant influence on the the state (Carr, 1967; Schmidt, 2001; Slade and state's climate, moderating its temperature and Patton, 2003). Texas is prone to hurricanes that precipitation. The El Niño Southern Oscillation also find their way into the Gulf of Mexico during the affects the state’s moisture patterns and is responsible hurricane season. The Rocky Mountains guide cold for long-term changes in Texas’ precipitation. fronts of arctic air moving southward into the state during the late fall, winter, and early and also extract much of the Pacific moisture from subtropical depressions carried eastward by subtropical west winds during the summer. During the spring and fall, warm, dry air from the high plains of northern Mexico is pulled into the state by the jet stream and collides with humid air from the Gulf of Mexico funneled in by the western limb of the Bermuda High system—resulting in severe and tornadoes.

5.1 Temperature, Precipitation, and Evaporation In general, average annual maximum daily temp- erature gradually increases from less than 70°F in the northern Panhandle to more than 82°F in the Lower , except for isolated mountainous areas of Far West Texas (Figure 5.2). In Far West Texas, the average annual maximum daily temperature sharply increases from less than 72°F in the Davis and Guadalupe mountains to more than 80°F in the Presidio and areas. Average annual precipitation decreases from over 55 inches in Beaumont to less than 10 inches in El Paso (Figure 5.3). Average annual gross lake sur-

130 Water for Texas 2007 Figure 5.1. The interaction of seasonal air masses and North American geography affecting the variability of Texas climate

(source data for base map Rocky Mountains from USGS, 2000). Arctic fronts

stream Jet Atlantic Ocean stream

Jet H Bermuda Mexican West winds Highlands High Gulf air

Pacific Gulf Ocean West winds of Mexico Tropical storms

Climate of Texas 131 face evaporation ranges from less than 45 inches in East Texas to more than 90 inches in Far 70 West Texas (Figure 5.4). 72 74 Although most of the state’s 70 precipitation occurs in the form of rainfall, small amounts 72 of ice and snow become in- 74 74 creasingly probable toward the 74 78 north and west. In addition, 76 76 76 the variability of both daily 76 temperature and precipitation 72 totals increase inland across 76 76 the state and away from the Gulf of Mexico. The majority 76 of rainfall in Texas occurs dur- 78 80 78 ing storm events when a large 80 80 80 amount of precipitation falls over a short period of time. 82 78 Except for the wetter, eastern Figure 5.2. Average annual 80 portion of the state, evapora- maximum daily temperature tion exceeds precipitation for (degrees Fahrenheit) for 1971 to 2000 (data from most of Texas, yielding a semi- SCAS, 2004). 82 arid climate that becomes arid in Far West Texas. Relative hu- midity varies throughout the state, depending on rainfall and evaporation rates, but gen- 20 erally decreases from east to west. 15

5.2 Climate 25 30 Divisions 35 40 45 50 The National Climatic Data Center divides Texas into 10 50 climate divisions (Figure 5.5). 15 Climate divisions represent 10 15 regions with similar climatic 55 characteristics, such as vege- 10 tation, temperature, , 10 rainfall, and seasonal weather changes. Data collected at lo- 20 55 cations throughout the state 15 are averaged within the divi- 20 20 20 50 sions in order to make maps 45 such as the one in Figure 5.5. 40 These divisions are commonly 40 35 used to report climatic infor- Figure 5.3. Average annual 30 mation, such as precipitation, precipitation (inches) for temperature, and drought in- 1971 to 2000 (data from 20 dices. SCAS, 2004). 25

132 Water for Texas 2007 5.3 Climate Influences The El Niño Southern Oscilla- 70 tion, a cyclical fluctuation of 65 60 55 ocean surface temperature 50 and air pressure in the tropical 75 Pacific Ocean, affects Pacific moisture patterns and is respon- sible for long-term (decadal) 80 45 changes in Texas’ precipitation, leading to periods of moderate 45 to severe drought. During a 85 weak oscillation, precipitation 90 will generally be below average and some degree of drought 85 90 50 will occur. However, during a 80 strong oscillation, Texas will 85 55 usually experience above aver- 60 age precipitation. Figure 5.4. Average annual gross lake surface The range between summer evaporation (inches) for and winter average monthly 1950 to 1979 (modified from 85 temperatures increases with Larkin and Bomar, 1983). 75 70 65 increased distance from the Gulf of Mexico (Figure 5.5). In

Climate of Texas 133 6 90 2 P = Precipitation in inches 4 60 P T T = Temperature in degrees Fahrenheit 2 30 6 90 3 0 0 4 60 6 90 J FMAMJJASON D 1 P T 2 30 4 60 P T 0 0 2 30 JFMAMJJASOND 6 90 0 0 1 4 J FMAMJJASON D 2 4 60 6 90 P T 5 2 30 4 60 3 P T 4 0 0 J FMAMJJASON D 2 30 5 6 6 90 0 0 8 JFMAMJJASOND 7 8 4 60 6 90 P T 6 2 30 4 60 9 0 0 P T JFMAMJJASOND 2 30 6 90 10 7 0 0 J FMAMJJASON D 4 60 6 90 P T 9 2 30 4 60 0 0 P T JFMAMJJASOND 2 30 6 90 10 0 0 J FMAMJJASON D 4 60 P T 2 30 Figure 5.5. Climate divisions of Texas with corresponding climographs showing average monthly precipitation 0 0 (vertical bars) and temperature (curved line) for 1971 J FMAMJJASON D to 2000 (data from NCDC, 2006).

addition, the state climate divisions nearest the about 30 percent below average. This drought Gulf Coast show more pronounced rainy seasons persisted for five to seven years throughout most in the fall and spring. These two rainy seasons are of the state (Figure 5.6). During the 1930s, north- affected by polar fronts interacting with moist ern and western parts of the state—along with a Gulf air during those seasons. The fall season also large portion of the central —experi- includes precipitation associated with hurricanes enced a drought compounded by poor agricultural and tropical depressions approaching or entering management practices that stripped away large the state from the Gulf of Mexico. volumes of top soil, known as the . More recently, portions of South, Central, and West 5.4 Climate Trends Texas have experienced recurrent periods of drought from the 1990s through 2006 (Figure 5.6). Some During the period of recorded precipitation from regions have experienced or are experiencing new 1895 to 2005, the most severe statewide drought droughts of record since the passage of Senate Bill 1, occurred during the 1950s when precipitation was 75th Legislative Session, in 1997. The geographic

134 Water for Texas 2007 120 Average = 18.9 inches 80 1 Climate division 40 0 -40 -80 120 80 2 Average = 23.6 inches 40 0 -40 -80 120 80 3 Average = 34.3 inches 40 0 -40 -80 120 80 4 Average = 46.4 inches 40 0 -40 -80 120 80 5 Average = 12.5 inches 40 0 -40 -80 120 80 6 Average = 25.4 inches 40 0 -40 -80 120 80 7 Average = 34.8 inches 40 0 -40 Departure from annual average precipitation (percent) -80 120 80 8 Average = 47.8 inches 40 0 -40 -80 120 80 9 Average = 23.3 inches 40 0 -40 -80 120 80 10 Average = 25.0 inches 40 0 -40 -80 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 Note: Light blue shading indicates drought of record in Texas.

Figure 5.6. Historical plots of percent departure from average annual precipitation for each climate division of Texas for 1895 to 2005 (data from NCDC, 2006).

Climate of Texas 135 location and consequential climatic variability References of the state creates the inevitability of recurrent drought interrupted by brief periods of floods. Carr, J.T., Jr., 1967, The climate and The frequency of droughts in the state is the rea- physiography of Texas: Texas Water Development son Senate Bill 1 required the water supply plan- Board Report 53, 27 p. ning process to meet water supply needs during Larkin, T.J., and Bomar, G.W., 1983, Climatic a drought of record and is one of the reasons for atlas of Texas: Texas Water Development the five-year cycle of review and update of the Board Limited Publication 192, 151 p. regional and state water plans. With the Senate Bill 1 planning process, the citizens of Texas will NCDC (National Climatic Data Center), 2006, always have an up-to-date assessment of the Climate visualization (CLIMVIS)—Climate division adequacy of their water supply during drought data: Asheville, NC, National Climatic Data conditions and the strategies and actions that Center, National Environmental Satellite Data will be required to meet water supply needs and Information Services, National Oceanic and during the inevitable return to drought. Atmospheric Administration, U.S. Department of Commerce, ASCII file, http://lwf.ncdc.noaa.gov/ oa/climate/onlineprod/drought/main.html, accessed March 2006. SCAS (Spatial Climate Analysis Service), 2004, Near-real-time monthly high-resolution precip- itation climate data set for the conter-minous United States (2.5-arc minute 1971–2000 mean monthly precipitation grids for the conterminous United States): Corvallis, OR, Spatial Climate Analysis Service, Oregon State University, Arc grid file, http://www.ocs.oregonstate.edu/prism/, accessed March 2006. Schmidt, R.H., 2001, The online, Trans-Pecos: Austin, TX, The General Libraries at the University of Texas at Austin and the Texas State Historical Association, http://www.tsha.utexas.edu/handbook/online/ articles/TT/ryt2.html, accessed June 2006. Slade, R.M., Jr., and Patton, J., 2003, Major and catastrophic storms and floods in Texas—215 major and 41 catastrophic events from 1853 to September 1, 2002: U.S. Geological Survey Open- File Report 03-193, Division, U.S. Geological Survey, U.S. Department of the Interior, http://pubs.usgs.gov/of/2003/ofr03- 193/cd_files/USGS_Storms/index.html, accessed June 2006. USGS (U.S. Geological Survey), 2000, Hydro 1K digital elevation model (DEM) for North America: Sioux Falls, SD, Earth Resources Observation and Science Center, U.S. Geological Survey, U.S. Department of the Interior, DEM file, http:// edc.usgs.gov/products/elevation/gtopo30/ hydro/na_dem.html, accessed March 2006.

136 Water for Texas 2007