1. 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

2. Outline Background on aquifers Drought information needs (ET, SM, GW) – Modeling and satellite products Example: 2011 drought in Texas

3. Major Aquifers in Texas

4. Groundwater Depletion in Texas Aquifers

5. Storativity: amount of water released from an aquifer for a decrease in water level. Unconfined aquifers 1 – 30% of water storage can be recovered Confined aquifers 0.005 – 0.5% of water in storage can be recovered

6. Typical Dipping Confined Aquifer Same aquifer: unconfined and confined

7. Gulf Coast Aquifer System Pre-Development Recharge Springflow and baseflow

8. Gulf Coast Aquifer System Post Development Recharge Pumping Recharge

9. 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

10. 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

11. 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

12. Data Needs Groundwater (NLDAS, GRACE) Recharge (NLDAS): P − ET = Recharge 500 ± 50 − 480 ± 48 = 20 ± 98 GRACE: ∆TWS = ∆ SMS + ∆ GWS Water Scarcity = Demand > Supply

13. 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)

14. Example of 2011 Drought in Texas

15. PDSI and GRACE Total Water Storage Long et al., 2013

16. Soil Moisture Storage

17. GRACE Gridded Product

18. 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