Geography

Austin Texas as seen from the International Space Station, 2007 City limits of Austin

Austin is located in Central Texas, along the Balcones Escarpment and Interstate 35, northwest of Houston. It is also 160 miles south of Dallas. Its elevation varies from 425 feet (130 m) to approximately 1,000 feet (305 m) above sea level. As of 2010, the city occupies a total area of 271.8 square miles (704 km2). Approximately 6.9 square miles (18 km2) of this area is water.

Austin is situated on the Colorado River, with three man-made (artificial) lakes within the city limits: Lady Bird Lake (formerly known as Town Lake), Lake Austin (both created by dams along the Colorado River), and Lake Walter E. Long that is partly used for cooling water for the Decker Power Plant. Mansfield Dam and the foot of Lake Travis are located within the city's limits. Lady Bird Lake, Lake Austin, and Lake Travis are each on the Colorado River. As a result of its straddling the Balcones Fault, the eastern part of the city is flat, with heavy clay and loam soils, whereas, the western part and western suburbs consist of rolling hills on the edge of the Texas Hill Country. Because the hills to the west are primarily limestone rock with a thin covering of topsoil, portions of the city are frequently subjected to flash floods from the runoff caused by thunderstorms. To help control this runoff and to generate hydroelectric power, the Lower Colorado River Authority operates a series of dams that form the Texas Highland Lakes. The lakes also provide venues for boating, swimming, and other forms of recreation within several parks on the lake shores.

Austin is located at the intersection of four major ecological regions, and is consequently a temperate-to-hot green oasis with a highly variable climate having some characteristics of the desert, the tropics, and a wetter climate. The area is very diverse ecologically and biologically, and is home to a variety of animals and plants. Notably, the area is home to many types of wildflowers that blossom throughout the year but especially in the spring, including the popular bluebonnets, some planted in an effort by "Lady Bird" Johnson, wife of former President Lyndon Johnson.

A popular point of prominence in Austin is Mount Bonnell. At about 780 feet (238 m) above sea level, it is a natural limestone formation overlooking Lake Austin on the Colorado River, with an observation deck about 200 feet (61 m) below its summit.

The soils of Austin range from shallow, gravelly clay loams over limestone in the western outskirts to deep, fine sandy loams, silty clay loams, silty clays or clays in the city's eastern part. Some of the clays have pronounced shrink-swell properties and are difficult to work under most moisture conditions. Many of Austin's soils, especially the clay-rich types, are slightly to moderately alkaline and have free calcium carbonate.

Climate Austin Climate chart (explanation) J F M A M J J A S O N D     2.2   62 41     2   65 45     2.8   72 51     2.1   80 59     4.4   86 67     4.3   92 72     1.9   95 74     2.4   97 75     3   91 70     3.9   82 61     3   71 51     2.4   63 42 Average max. and min. temperatures in °F Precipitation totals in inches Metric conversion J F M A M J J A S O N D     56   16 5     51   18 7     70   22 11     53   27 15     112   30 19     110   33 22     48   35 24     60   36 24     76   33 21     99   28 16     75   22 10     61   17 6 Average max. and min. temperatures in °C Precipitation totals in mm

Austin has a humid subtropical climate (Köppen: Cfa), characterized by hot summers and mild winters. Austin is usually at least partially sunny, receiving nearly 2650 hours, or 60.3% of the possible total, of bright sunshine per year.

Austin summers are usually hot, with average July and August highs in the high-90s °F (34–36 °C). Highs reach 90 °F (32.2 °C) on 116 days per year, and 100 °F (37.8 °C) on 18. The highest recorded temperature was 112 °F (44 °C) occurring on September 5, 2000 and August 28, 2011

Winters in Austin are mild and relatively dry. For the entire year, Austin averages 88 days below 45 °F (7.2 °C) and 13 days when the minimum temperature falls below freezing. The lowest recorded temperature was −2 °F (−19 °C) on January 31, 1949. About every two years or so, Austin experiences an ice storm that freezes roads over and affects much of the city for 24 to 48 hours. Snowfall is rare in Austin; a 3-inch (7.6 cm) snowstorm brought the city to a near standstill in 1985.

Monthly averages for Austin's weather data are shown in a graphical format to the right, and in a more detailed tabular format below.

Climate data for Camp Mabry, Austin, Texas (1981–2010 normals) Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Record high °F (°C) 90 (32) 99 (37) 98 (37) 99 (37) 104 (40) 109 (43) 109 (43) 112 (44) 112 (44) 100 (38) 91 (33) 90 (32) 112 (44) Average high °F (°C) 61.5 (16.4) 65.2 (18.4) 72.2 (22.3) 79.8 (26.6) 86.5 (30.3) 92.1 (33.4) 95.6 (35.3) 97.0 (36.1) 90.5 (32.5) 81.8 (27.7) 71.4 (21.9) 62.7 (17.1) 79.7 (26.5) Average low °F (°C) 41.5 (5.3) 44.8 (7.1) 51.3 (10.7) 58.6 (14.8) 66.7 (19.3) 72.3 (22.4) 74.4 (23.6) 74.6 (23.7) 69.4 (20.8) 60.6 (15.9) 50.6 (10.3) 42.3 (5.7) 58.9 (14.9) Record low °F (°C) −2 (−19) −1 (−18) 18 (−8) 30 (−1) 40 (4) 51 (11) 57 (14) 58 (14) 41 (5) 30 (−1) 20 (−7) 4 (−16) −2 (−19) Precipitation inches (mm) 2.22 (56.4) 2.02 (51.3) 2.76 (70.1) 2.09 (53.1) 4.41 (112) 4.33 (110) 1.88 (47.8) 2.35 (59.7) 2.99 (75.9) 3.88 (98.6) 2.96 (75.2) 2.40 (61) 34.29 (871.1) Snowfall inches (cm) .4 (1) .2 (0.5) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) .6 (1.5) Avg. precipitation days (≥ 0.01 in) 7.4 7.4 9.2 7.1 8.9 7.7 5.4 4.9 6.7 7.5 7.5 7.8 87.6 Avg. snowy days (≥ 0.1 in) .2 .3 0 0 0 0 0 0 0 0 0 0 0.5 Mean monthly sunshine hours 164.3 169.5 204.6 207.0 226.3 285.0 316.2 297.6 234.0 217.0 168.0 155.0 2,644.5 Source: NOAA (extremes 1897–present), Weather.com , Hong Kong Observatory (sun only, 1961–1990)

2011 drought Main article: 2011 Southern US drought The 2011 Texas drought dried up much of Central Texas water ways. This boat was left to sit in the middle of what is normally a branch of Lake Travis, part of the Colorado River.

From October 2010 through September 2011, Austin had the least rainfall since the 1950s. This was a result of La Niña conditions in the eastern Pacific Ocean where water was significantly cooler than normal. Dr. David Brown, a regional official with the National Oceanic and Atmospheric Administration, has explained that "these kinds of droughts will have effects that are even more extreme in the future, given a warming and drying regional climate."