EXTREME WEATHER EVENTS AND AQUIFER RESPONSES IN THE BALCONES FAULT ZONE EDWARDS AQUIFER OF SOUTH-CENTRAL TEXAS (Invited Presentation)

South-Central Texas is noted for extreme weather events that include both rainfall/flooding and drought. Rainfall events may be associated with hurricane systems moving from the Gulf of Mexico or the Pacific Ocean. However, stalled weather fronts have also been responsible for intense rainfall events when warm moist air from the Gulf of Mexico or Pacific Ocean meet a high pressure system that has stalled over the Texas Hill Country. Rainfall amounts of as much as 38 inches in 24 hours and 23 inches of rain in 12 hours have been recorded. Rainfall events in 1921, 1935, 1954, 1972, 1987, 1991, 1998, 2002, 2013, and 2015 caused widespread flooding, property damage, and loss of life. Water levels in some Edwards Aquifer wells rose more than 100 feet in 48 hours during extreme events.

The area has also experienced record droughts from 1951 to 1956, which was probably the driest in hundreds of years, and from 2009 to 2013, during which 2011 set a record for the hottest, driest one-year period throughout much of Texas. Droughts have resulted in economic devastation to the agricultural community. Water withdrawals from the Edwards Aquifer are now regulated to protect critical habitat for endangered species during droughts.

The correlation of ENSO index to rainfall for south-central Texas and recharge to the Edwards Aquifer is generally weak, but all seven of the largest monthly recharge estimates for the Edwards Aquifer have all occurred during moderate to strong El Niño conditions.

EAA was created to protect threatened and endangered species habitat at Comal and San Marcos springs from extreme weather. Groundwater management policies instituted by EAA achieved significant improvements in springflow and water levels compared to previous severe droughts. EAA obtained a Habitat Conservation Permit to manage the springs habitat during extreme weather events in the future.