Drought Information Needs for Water Resources Management: Texas as a Case Study

Bridget R. Scanlon, Rong Fu, Todd Caldwell, Di Long, and Nelun Fernando

Jackson School of Geosciences, Univ. of Texas at Austin

Outline

• Background on aquifers• Drought information needs (ET, SM, GW)

– Modeling and satellite products• Example: 2011 drought in Texas

Major Aquifers in Texas

Groundwater Depletion in Texas Aquifers

Storativity: amount of water released from an aquifer for a decrease in water level.

Unconfined aquifers1 – 30% of water storage can be recovered

Confined aquifers 0.005 – 0.5% of water in storage can be recovered

Typical Dipping Confined Aquifer

Same aquifer: unconfined and confined

Gulf Coast Aquifer SystemPre-Development

RechargeSpringflow and baseflow

Gulf Coast Aquifer SystemPost Development

Recharge PumpingRecharge

Implications for Using Model and Satellite Data

• Ogallala Aquifer: demand driven system, not really impacted directly by changes in recharge but indirectly affected by pumpage

• Confined aquifers: disconnected from surface water, recharged thousands of years ago, only impacted by drought indirectly through pumpage

Information Needs

• Groundwater planning time horizon: 50 yr, 2010 – 2060• Based on 1950s drought• National drought maps and archives with time series are very

valuable, extend back to 1900?• Climate in next 50 yr: 1 yr extreme droughts? Longer term droughts? • How well can we predict beginning of droughts? Persistence?, end

of droughts? • Seasonal drought predictions: fall – early spring: water transfers if

drought predicted• Not irrigate if predict intense drought? • Daily temperature data for electricity sector

Data Needs

• Evapotranspiration (MODIS, Landsat, NLDAS): – Irrigation needs

• Soil moisture storage (SMAP, NLDAS): – Irrigation needs – Drought persistence…feedback– Precipitation requirements for reservoir recovery– Flood predictions

Data Needs

• Groundwater (NLDAS, GRACE)• Recharge (NLDAS): P − ET = Recharge 500 ± 50 − 480 ± 48 = 20 ± 98 • GRACE:∆TWS = ∆ SMS + ∆ GWSWater Scarcity = Demand > Supply

Satellite and Modeling Products

• Satellite ET, GRACE derived ET, and LSM ET• Satellite ET unconstrained by water balance (1 km

resolution)• Model ET more reliable, coarse ( 14 km resolution)• GRACE GW, LSM GW• Difficult to disaggregate GRACE TWS into

components with large variability in LSM SMS• LSM provide upper BC for groundwater

(unconfined aquifers)

Example of 2011 Drought in Texas

PDSI and GRACE Total Water Storage

-120

-80

-40

0

40

80

120

km

3

-200

-150

-100

-50

0

50

100

150

200

Totalw

aterstorageanomalies(m

m)

GRGS RL02CSR RL05PDSI

-10

-8

-6

-4

-2

0

2

4

6

8

10

PDSI

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

-40

0

40

80

120

(mm)

-40

-20

0

20

40

60

80

km

3

Precip. anomal

Long et al., 2013

Soil Moisture Storage

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

-80

-40

0

40

80

120

km3

-150

-100

-50

0

50

100

150

200

Soilmoistureandtotalw

aterstorage

anomalies(mm)

NLDAS-2 Noah

NLDAS-2 Mosaic

GLDAS-1 Noah

GLDAS-1 Mosaic

GLDAS-1 VIC

GLDAS-1 CLM

CSR RL05

GRACE Gridded Product

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Wa

ter

sto

rage

ano

ma

lies

(mm

)

-200

-150

-100

-50

0

50

100

150

200

(km3)

-120

-90

-60

-30

0

30

60

90

120

CSRGFZJPLAlgorithm1

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Precipanomaly(m

m)

-100-50

050

100150

-50

0

50

100

(km3)

Summary

• Information needs for drought:– Long-term planning, 1 yr versus multiyear droughts?– Seasonal forecasting: 6 – 9 months– Daily data: temperature, heat waves– Archive data back to 1900

• Satellite data: ET, irrigation demand; soil moisture

• Modeling: upper boundary condition for unconfined aquifers