RAINFALL DEFICITS, RECHARGE, AND SURVIVING DROUGHT

IN THE EDWARDS AQUIFER REGION

PRESENTATION TO WATER ENVIRONMENT ASSOCIATION OF TEXAS SUMMER SEMINAR SERIES

JULY 24,2015

JIM WINTERLE. P.G. , DIRECTOR OF MODELING AND DATA MANAGEMENT

MARK HAMILTON, P.G., EXECUTIVE DIRECTOR, AQUIFER MANAGEMENT SERVICES

JENNA PACE, ENVIRONMENTAL COORDINATOR

SARAH EASON, GIS ANALYST

Assessing Rainfall Deficit from 2003-2014 • At beginning of 2015, drought maps showed

widespread improvements in drought conditions in Central Texas, but groundwater levels remained low.

• Questions about why recharge has been far below average when rainfall was near average for the past two years

• Summary of rainfall deficits, annual recharge, and

water levels January 1, 2003 – December 31, 2014.

This map shows the EAA precipitation gauging network. • Over 70 automated gauges

• Data used to calibrate NEXRAD

• Calibrated NEXRAD data used

for detailed region wide rainfall totals

Background

Expected Rainfall for a 12-Year Period Based on NWS 30-year Average from 1981-2010

2003 to 2014 Actual Rainfall

12-year Cumulative Deficit

Compared to a regional mean annual rainfall of 30” an 82” deficit equates to:

Missing 2.7 Years of rainfall for the period.

Regional Mean Statistics

Compared to a regional mean annual rainfall of 30” A worst case deficit (-130”) equates to:

Missing 4.3 years of rainfall over the 12-year period.

Deficit Rainfall Statistics, 2003-2014

Including Drought of Oct. 2010 to Sept. 2011

Although the Drought Maps Show Improvements in Recent Months Water Levels Do Not

Annual Rainfall Deficit

Index Well Water Levels

Annual Recharge

Recharge 2003-2014 Mean = 660,500 Median = 263,200 Recharge 1934-2014 Mean = 692,100 AF Median = 556,100 AF

In the most recent 12-year period, 7 of the years are below average. Over 50-percent of the total recharge for this period occurred in 2004 and 2007. 4.3 million AF (2004 and 2007) 3.6 million AF (remaining years)

More rigorous analyses of recharge is underway using Puente and HSPF.

Differences in Recharge Between Years 2011 and 2014

The cumulative effect of contiguous dry years impacts stream flows which impacts recharge.

2015 Recovery from the Drought Rainfall totals for January-June, 2015

2015 Recovery from the Drought

2015 Recovery from the Drought

Conclusion • Regional rainfall deficits are quite significant over the twelve year period 2003 –

2014, averaging -82 inches across the Edwards Aquifer region. • The regional mean rainfall deficit for the period 2008 – 2014, is -71 inches.

(Equivalent to 2.3 out of 7 years with no rainfall based on a 30-inch annual mean) • Cumulative deficit can reduce annual recharge to far below average even when

rainfall is only slightly below average • Timing and location of rainfall is also important to recharge

• Recovery of aquifer levels in 2015 shows that we don’t need to make up the all of

the cumulative deficit to get good recharge

• Total long-term recharge to the aquifer tends to be dominated by relatively few wet years

• Conservation measures under EAA Act have helped to sustain water levels through the recent drought

�rainfall Deficits, recharge, and Surviving drought in the Edwards Aquifer Region����presentation to water environment association of Texas�summer seminar series�july 24,2015Slide Number 2Slide Number 3Expected Rainfall for a 12-Year Period�Based on NWS 30-year Average from 1981-20102003 to 2014 Actual RainfallSlide Number 6Slide Number 7Deficit Rainfall Statistics, 2003-2014Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23