THIS 3-YEAR PROJECT IS COLLABORATION BETWEEN SCIENTISTS FROM TWO UNIVERSITIES (ASU AND BGSU) AND JPL WITH THE AIM TO SIGNIFICANTLY IMPROVE RESOLUTION AND ACCURACY OF CURRENT ESTIMATES OF TOTAL WATER MASS BUDGET VARIATIONS OVER CALIFORNIA. THE SUCCESS OF THE PROJECT RELIES ON CAREFUL ANALYSIS AND COMBINATION OF INSAR GPS AND GRACE DATA SETS. TO THIS END THE FOLLOWING GOALS ARE ENVISIONED: 1. GENERATING MAP OF LARGE SCALE (~1000 KM) HIGH RESOLUTION (~500 M) AND TIME-DEPENDENT (2003 - 2018) 3D SURFACE DEFORMATION BY COMBINING ALL AVAILABLE GPS DATA AND LARGE SETS OF SAR IMAGES ACQUIRED BY ENVISAT ALOS 1&2 SENTINEL-1 TERRASAR-X COSMO- SKYMED SATELLITES. 2. APPLYING A BAYESIAN TIME-DEPENDENT MODELING SCHEME TO INVERT GRAVITY AND DEFORMATION DATA AND TO CONSTRAIN THE LOCAL POROELASTIC AQUIFER DEFORMATION CAUSED BY PUMPING AND TWS VARIATIONS LINKED TO REGIONAL ELASTIC LOADING AT 1000 M RESOLUTION. 3. APPLYING A STATISTICAL FRAMEWORK TO TAKE INTO ACCOUNT ALL DATA ERRORS AND MODEL UNCERTAINTIES TO ESTIMATE UNCERTAINTIES ASSOCIATED WITH OBTAINED TWS VARIATIONS SUITABLE FOR DROUGHT FORECAST MODELS. 4. IMPLEMENTING A KALMAN FILTER FRAMEWORK TO FILL GAPS IN GRACE DATA AVAILABILITY TO ASSURE THE CONTINUITY OF TWS ESTIMATES UNTIL GRACE-FO IS IN ORBIT. AN IMPROVED UNDERSTANDING OF THE SPATIOTEMPORAL VARIATIONS OF TWS CAN BE USED TO ASSESS THE RECHARGE WITHDRAWAL AND FLUXES OF WATER THROUGH THE HYDROLOGICAL WATER CYCLE. IT ACCOUNTS FOR VARIATIONS IN WATER AMONG ALL STORAGES THUS IT ALLOWS QUANTIFYING THE TOTAL CHANGE IN AVAILABILITY OF WATER FOR A REGION AND THEREWITH ESTIMATING SEVERITY OF AN UPCOMING DROUGHT. STATES ACROSS SOUTHWEST USA IN PARTICULAR CALIFORNIA ARE CURRENTLY UNDERGOING A SEVERE DROUGHT ON LARGE SPATIAL EXTENTS WHICH CAUSES SHRINKAGE OF THE SURFACE AND GROUNDWATER RESOURCES. THUS A COMPREHENSIVE MONITORING AND MODELING SCHEMES TO ENHANCE DROUGHT MANAGEMENT AND MITIGATING THE NEGATIVE IMPACTS AT VARIOUS SPATIAL AND TEMPORAL SCALES IS AN ESSENTIAL. THE PROPOSED RESEARCH EFFORT WILL PERFORM A JOINT ANALYSIS OF THE DEFORMATION AND GRAVITY DATA TO OBTAIN MAPS OF TWS VARIATIONS ON VARIOUS SCALES RANGING FROM 100S OF M TO 1000S OF KM. TO THIS END WE WILL ANALYZE THE ARCHIVE OF GRAVITY DATA OBTAINED BY GRACE SATELLITES (2002-PRESENT) AND THE HIGH RESOLUTION 3D DEFORMATION DATA OBTAINED THROUGH INSAR PROCESSING OF THE SAR IMAGES ACQUIRED BY VARIOUS SATELLITES (2003-PRESENT) AND GPS MEASUREMENTS OVER THE STATE OF CALIFORNIA. COMBINATION OF THE HIGH RESOLUTION DEFORMATION DATA AND CONTINUOUS GRAVITY OBSERVATIONS THROUGH A BAYESIAN INVERSE MODELING SCHEME PROVIDES MULTISCALE ESTIMATES OF WATER STORAGES VARIATIONS AND ITS UNCERTAINTY. THUS IT PROVIDES UNIQUE CONSTRAINTS ON THE TIMING AND EXTENT OF HYDROLOGICAL MASS FLUXES USEFUL FOR PROBABILISTIC DROUGHT FORECAST AND MANAGEMENT. RESULTS FROM THIS PROJECT WILL ASSESS THE CAPABILITIES OF INSAR IN COMBINATION WITH GRACE AND GPS DATA TO PROVIDE HIGH RESOLUTION SPATIOTEMPORAL OBSERVATIONS OF TWS VARIATIONS. A BYPRODUCT OF THIS PROJECT IS THE LARGE SCALE MAP OF SURFACE DEFORMATION ACROSS CALIFORNIA WHICH IS USEFUL FOR VARIOUS ENGINEERING AND SCIENTIFIC APPLICATION. THUS BROAD LONG TERM BENEFITS ARE EXPECTED. THROUGH OUTREACH PROGRAMS WE WILL MENTOR HIGH SCHOOL STUDENTS IN PARTICULAR FEMALES AND UNDERREPRESENTED MINORITIES TO ENCOURAGE THEM PURSUE A CAREER IN SCIENCE AND ENGINEERING. THIS PROJECT PROVIDES SUPPORT FOR TWO PH.D. STUDENTS FOR TWO YEARS AND PARTIAL SUPPORTS FOR 3 EARLY CAREER SCIENTISTS. IT WILL ALSO ALLOW DEVELOPING NEW TECHNOLOGY-BASED AND LEARNER-CENTERED CURRICULA FOR UNDERGRADUATE COURSES. ALL TOOLS DEVELOPED AND RESULTS OBTAINED HEREIN WILL BE DOCUMENTED AND AVAILABLE TO THE ENGINEERING AND EARTHSCIENCE COMMUNITIES AS OPEN SOURCE.