Climate
Using the data displayed above and Koppen’s Climate Classification, it was determined that the climate classification of Austin, Texas is Cfa, or humid subtropical. This climate classification is characterized by hot summers, mild winters, and regular precipitation year round. The overall amount of precipitation in this region is by no means extreme, however the region doesn’t have slow, steady rainfalls. It isn’t uncommon for a single rainfall to produce over three inches (76 mm) of precipitation, and severe rainfalls can produce at least 14 inches (356 mm) of precipitation. When looking at the average monthly rainfalls in the data provided, it can be seen that this is a fairly substantial amount in a single rinfall. This means that the region can be without rainfall for several days, even weeks at a time. This can often lead to misconceptions of the area being a somewhat dry place, but when large rainfalls hit, that misconception is corrected altogether.
Geographic Location
The storms that produce these rainfalls occur because of the geographic location of the Hill Country in the North American continent. To the southeast lies the Gulf of Mexico, to the northwest lies the Rocky Mountains, and a great portion of the inland continent. These two factors contribute to create the storms that are capable of producing large rainfalls. This happens when warm, moist air from the Gulf Coast meets with dry, cooler air from the Rocky Mountains. Whenever this combination occurs, it creates instability in the atmosphere, which then leads to the production of large storm clouds. Often, this mixing of air happens when a trough
in the Jetstream forms, bringing dry air from the north down to the
southeastern coastal region of Texas. When this happens, a cold front pushes
southward lifting the warmer moist airfrom the Gulf Coast, creating large storm
clouds over the Texas Hill Country. This process can easily be seen in the figure above.
Not only are severe thunderstorms frequent in the area, but tropical cyclones (also known as hurricanes) bring severe weather to the Texas Hill Country area. Hurricanes form over water, and require moisture to continue on their destructive path. Because of this, Central Texas is safe from the destruction that these powerful storms bring to the coast. However, significant precipitation is still carried over the Texas Hill Country as the cyclone moves inland and dissipates. Both hurricanes and severe thunderstorms bring immense rainfall to Central Texas, as a result of the region’s precise location on the continent.
Not only are severe thunderstorms frequent in the area, but tropical cyclones (also known as hurricanes) bring severe weather to the Texas Hill Country area. Hurricanes form over water, and require moisture to continue on their destructive path. Because of this, Central Texas is safe from the destruction that these powerful storms bring to the coast. However, significant precipitation is still carried over the Texas Hill Country as the cyclone moves inland and dissipates. Both hurricanes and severe thunderstorms bring immense rainfall to Central Texas, as a result of the region’s precise location on the continent.
Surfaces & Topography
The Texas Hill Country is also susceptible to flash floods due to the nature of the surfaces in the region – both natural and man made. Due to the proximity to the Edwards Plateau, above the Edwards Aquifer, this region has a very thin topsoil and large amounts of exposed bedrock, which produces a lot of runoff in the area. Normally the Edwards Aquifer recharges quickly, however this isn't the case with very large, intense rainfalls. Although water enters the Aquifer easily in the recharge zone, the drainage is generally inadequate to hold all the water that falls in large rain events. This thin topsoil doesn't absorb precipitation as fast as it falls, so the water has nowhere to go but over the surface. Likewise, natural impervious surfaces like bedrock do not help with the ground penetration of rainfall, so the precipitation is forced to flow across the surface.
In addition to these natural impervious surfaces are those impervious surfaces that humans have produced in the area. Cities that are at the edge of the Texas Hill Country (such as San Marcos, New Braunfels, Buda, Kyle, and Austin) contribute to the runoff, due to the quantities of sidewalks, roads, and other such surfaces that do not allow precipitation to be absorbed into the soil. As such, these areas often experience severe damage due to floods caused by insufficient drainage. This problem with runoff is also amplified due to the topography of the Central Texas region. Within Central Texas is the Balcones Escarpment, which is the transitional area between the coastal plains of southeastern Texas and the Hill Country of Central Texas. Considerably more runoff happens in the Hill Country than the coastal plains, and this change can be seen as the landscape changes within the Balcones Escarpment. It is obvious that large elevation changes would create an increase of runoff, and the Texas Hill Country is no exception.
In addition to these natural impervious surfaces are those impervious surfaces that humans have produced in the area. Cities that are at the edge of the Texas Hill Country (such as San Marcos, New Braunfels, Buda, Kyle, and Austin) contribute to the runoff, due to the quantities of sidewalks, roads, and other such surfaces that do not allow precipitation to be absorbed into the soil. As such, these areas often experience severe damage due to floods caused by insufficient drainage. This problem with runoff is also amplified due to the topography of the Central Texas region. Within Central Texas is the Balcones Escarpment, which is the transitional area between the coastal plains of southeastern Texas and the Hill Country of Central Texas. Considerably more runoff happens in the Hill Country than the coastal plains, and this change can be seen as the landscape changes within the Balcones Escarpment. It is obvious that large elevation changes would create an increase of runoff, and the Texas Hill Country is no exception.