ATTRIBUTING THE CAUSES OF A CENTURY OF WETTING IN THE EASTERN UNITED STATES USING OBSERVATIONS, MODELS, AND TREE RINGS

IN THE COMING DECADES NATURALLY DRIVEN CLIMATE VARIATIONS AROUND THE WORLD WILL FORCE LOW-FREQUENCY CHANGES IN REGIONAL WATER AVAILABILITY THAT MAY COUNTER OR AMPLIFY HYDROCLIMATIC TRENDS PROJECTED TO RESULT FROM ANTHROPOGENIC CLIMATE CHANGE. PRELIMINARY ANALYSIS OF OBSERVATIONAL RECORDS INDICATES THAT A DOMINANT MODE OF HYDROCLIMATE VARIABILITY IS A ZONAL DIPOLE ACROSS THE CONTINENTAL US THAT IS CHARACTERIZED BY AN EAST-WEST CONTRAST IN SUMMER SOIL-MOISTURE ANOMALIES. THIS ZONAL DIPOLE FOLLOWS A POSITIVE TREND OVER THE PAST CENTURY ASSOCIATED WITH A WETTING EAST AND DRYING WEST. THIS ONGOING AND UNDIAGNOSED TREND HIGHLIGHTS A CRITICAL UNCERTAINTY IN HOW HUMAN AND NATURAL SYSTEMS WILL BE IMPACTED BY CHANGES IN WATER SUPPLY IN THE FUTURE. I PROPOSE TO DIAGNOSE THE PHYSICAL ORIGINS AND SEASONALITY OF OBSERVED WETTING ACROSS MUCH OF THE EASTERN US OVER THE PAST CENTURY AND DETERMINE THE DEGREE TO WHICH THIS TREND HAS BEEN DYNAMICALLY ASSOCIATED WITH DRYING TRENDS IN THE WESTERN US AS WELL AS THE ZONALLY CONTRASTING TRENDS IN TEMPERATURE. I WILL ALSO INVESTIGATE THE ROLE OF ANTHROPOGENIC FORCING IN PROMOTING THESE TRENDS. USING SATELLITE-DERIVED REANALYSIS WEATHER STATION CLIMATE MODEL SIMULATIONS AND TREE-RING RECONSTRUCTED DROUGHT DATASETS I WILL DIAGNOSE THE CAUSES OF THE ZONALLY DIVERGING TRENDS IN PRECIPITATION AND TEMPERATURE AND DETERMINE IF THESE TRENDS ARE DYNAMICALLY RELATED. FIRST I WILL IDENTIFY LARGE-SCALE ATMOSPHERIC CIRCULATION PATTERNS TRENDS IN STORM TYPES AND SEASONALITY ASSOCIATED WITH ZONAL MODES OF SOIL-MOISTURE AND PRECIPITATION VARIABILITY. SECOND I WILL INVESTIGATE THE SPATIOTEMPORAL VARIABILITY IN US SOIL MOISTURE AND PRECIPITATION ON DECADAL TO CENTENNIAL TIMESCALES OVER THE LAST MILLENNIUM TO DETERMINE WHAT TIMESCALES THE ZONAL DIPOLE MODES HAVE BEEN MOST ACTIVE OVER THE LAST MILLENNIUM. THIRD I WILL DETERMINE IF THE OBSERVED INCREASES IN PRECIPITATION IN THE EASTERN US ARE DYNAMICALLY RELATED TO DRYING TRENDS IN THE WESTERN US AND DETERMINE THE DEGREE TO WHICH THE PRECIPITATION TRENDS ARE RELATED TO REDUCED WARMING IN THE EASTERN US. LAST I WILL USE REANALYSIS CLIMATE DATA AND CLIMATE MODEL OUTPUTS INCLUDING COUPLED MILLENNIAL AND SST-FORCED SIMULATIONS TO DIAGNOSE CAUSES OF LOW-FREQUENCY PRECIPITATION VARIABILITY AND THE POTENTIAL ROLE OF ANTHROPOGENIC FORCING. MY RESEARCH WILL DRAW HEAVILY FROM NASA S SUITE OF DATA PRODUCTS PARTICULARLY MERRA-2 GPCP GRACE MODIS AND SMAP. THIS PROJECT WILL BE PARTICULARLY RELEVANT TO THE SECOND STRATEGIC GOAL OF THE NASA SCIENCE MISSION DIRECTORATE ADDRESSING THE CAUSES OF A CHANGING EARTH SYSTEM IDENTIFYING FUTURE CHANGES AND PROMOTING SOCIETAL BENEFITS OF EARTH SYSTEM SCIENCE. SPECIFICALLY THIS RESEARCH WILL IDENTIFY THE DYNAMICAL FOUNDATIONS OF CENTURY LONG HYDROCLIMATIC TRENDS IN THE CONTINENTAL US EVALUATE THE ROLE OF ANTHROPOGENIC CONTRIBUTION IN A CHANGING CLIMATE AND IMPROVE OUR UNDERSTANDING OF CLIMATIC PROCESSES IMPACTING WATER RESOURCES THAT WILL IMPACT TENS OF MILLIONS OF PEOPLE ACROSS THE US.