GPS analysis of ground surface deformation in response to 2011 drought in Texas

Tuesday, 16 December 2014
Makan A. Karegar, Timothy H Dixon and Rocco Malservisi, University of South Florida, TAMPA, FL, United States
A precise process and analysis of a dense network of CGPS observations are used to infer the long term and seasonal deformation patterns of ground surface over the state of Texas. The state covers 9 major aquifers which supply more than 50 percent of the water utilized in the state and spread over ~75% of the state area. Pumping of groundwater from many aquifers for irrigation, industrial and human consumption has resulted in a significant water level declines, and in many areas caused long term ground surface subsidence. While more than 70 percent of GPS sites, located on the top of aquifers, experience subsidence, the remained sites located outside the aquifers present significant uplift as a result of elastic response to the changes in loading due to soil moisture and surface water. However, a significant episodic uplift (up 6 mm/yr) from 2010 to 2012 appears in all GPS time series corresponding to 2011 extreme drought in Texas and adjacent states. Such episodic uplift is inferred as an elastic response of ground surface to reduced surface load. While most of drought indicators rely on precipitation index, soil moisture model, satellite vegetation health index and streamflow data, we suggest using regional CGPS vertical displacement as a further proxy for the indication of a drought. Inverting the vertical displacement from GPS it is possible to estimate total water storage including the portion of groundwater storage. In this abstract, the uplifts during drought period are inverted to derive total water storage loss using load Green’s function. The GPS-based estimate of water loss is compared with GRACE-based and Land Surface Models estimates of total water storage (e.g. NLDAS and GLDAS). The limitations and uncertainty associated with each technique are discussed.