TERRESTRIAL WATER ECOSYSTEMS AND CLIMATE ARE INTIMATELY COUPLED DYNAMIC COMPONENTS OF THE EARTH'S SYSTEM. IN RESPONSE TO ELEVATED CO2 AND THE RESULTING WARMING TERRESTRIAL WATER AND ECOSYSTEMS HAVE BEEN EXPERIENCING SUBSTANTIAL CHANGES E.G. GLOBALLY SHRINKING SNOWPACK GREENING PLANTS EARLIER BLOOMING AND LEAFING OUT AND DEPLETING GROUNDWATER. THE "MEMORY" OF CLIMATE CHANGE RETAINED IN THE SLOWLY VARYING STATES OF SNOW SOIL WATER AND GROUNDWATER CAN PERSIST VARIABLY FROM SEASONS TO YEARS FEEDING BACK TO CLIMATE VARIABILITY WITH VARYING ENERGY AND WATER FLUXES MAINLY VIA PLANT ROOTS AND STOMATA. BASED ON THE WIDELY USED NOAH LAND SURFACE MODEL (LSM) NOAH-MP SYSTEMATICALLY IMPROVES THE REALISM OF SNOW SOIL WATER GROUNDWATER AND VEGETATION SCHEMES AND ENHANCES THE TERRESTRIAL WATER AND ECOSYSTEM DYNAMICS. HOWEVER WHETHER THE ENHANCED DYNAMICS AND IMPROVED REALISM OF TERRESTRIAL WATER AND ECOSYSTEMS HELP IMPROVE CLIMATE PREDICTIONS HAS NOT BEEN INVESTIGATED. LIKE MANY OTHER LSMS NOAH-MP USES STATIC SHALLOW REPRESENTATIONS OF ROOTS AND NEGLECTS ROOT DYNAMICS RESULTING IN LOW ECOSYSTEM RESILIENCE TO DROUGHT AND A SHORTER CLIMATE "MEMORY." WE PROPOSE TO 1) ANALYZE SEASONAL AND INTER-ANNUAL VARIABILITY AND LONG-TERM TREND OF THE TERRESTRIAL WATER ECOSYSTEM AND CLIMATE DYNAMICS USING THE GROUND-BASED AND SATELLITE DATA OF TEMPERATURE PRECIPITATION SNOW TERRESTRIAL WATER STORAGE (TWS) ANOMALIES STREAMFLOW AND LEAF AREA INDEX ETC.; 2) ANALYZE THE COUPLING DYNAMICS OF SNOW SUBSURFACE WATER VEGETATION AND CLIMATE USING A NEW "COUPLING STRENGTH" BASED ON OBSERVATIONS OF STREAMFLOW AND TWS CHANGE OVER RIVER BASINS IN THE CONTIGUOUS US (CONUS); 3) DEVELOP AND IMPLEMENT AN OPTIMALITY BASED DYNAMIC ROOT MODEL INTO NOAH-MP WHICH DESCRIBES OPTIMAL ADAPTATION OF THE ROOT PROFILE TO THE SOIL MOISTURE PROFILE TO MAINTAIN SUFFICIENT WATER IN PLANT TISSUES TO MEET TRANSPIRATION DEMAND; 4) COUPLE NOAH-MP WITH THE NASA LAND INFORMATION SYSTEM (LIS) AND CONDUCT OFFLINE EXPERIMENTS DRIVEN BY THE NORTH AMERICAN LAND DATA ASSIMILATION SYSTEM (NLDAS) AND THE MODERN-ERA RETROSPECTIVE ANALYSIS FOR RESEARCH AND APPLICATIONS (MERRA)-LAND ATMOSPHERIC FORCINGS; 5) COUPLE NOAH-MP WITH THE NASA-UNIFIED WEATHER RESEARCH AND FORECASTING MODEL (NU-WRF) AND CONDUCT COUPLED MODEL EXPERIMENTS IN THE CONUS USING NU-WRF/NOAH AND NU-WRF/NOAH-MP DRIVEN BY MERRA 2 REANALYSIS DATA. WE WILL TEST THREE MAJOR HYPOTHESES: H1: WITH MORE REALISTIC SCHEMES OF SNOW GROUNDWATER AND LEAF AND ROOT DYNAMICS NOAH-MP/NU-WRF WILL PRODUCE MORE REALISTIC TERRESTRIAL WATER AND ECOSYSTEM STATES AS WELL AS MORE REALISTIC CLIMATOLOGY AND CLIMATE VARIABILITY THAN NOAH/NU-WRF. H2: INCLUDING LEAF AND ROOT DYNAMICS THAT CAN ADAPT TO CLIMATE CHANGE WILL ENHANCE TERRESTRIAL ECOSYSTEM RESILIENCE AND TRANSPIRATION AND PRODUCE MORE REALISTIC CLIMATE VARIABILITY. H3: SHRINKING SNOW COVER HAS ACCELERATED WARMING OVER THE CONUS SINCE THE 1980S THROUGH POSITIVE SNOW-ALBEDO FEEDBACK; LESS (MORE) SNOW ACCUMULATION IN WINTER MAY RESULT IN LESS (MORE) SNOWMELT WATER INFILTRATING THE SOIL IN SPRING AND HENCE LESS (MORE) VIGOROUS VEGETATION AND A CONSEQUENT EFFECT ON SUMMER TEMPERATURE AND PRECIPITATION. THIS PROPOSAL IS A DIRECT REPLY TO THE MAP THEME OF "COUPLING IN THE EARTH SYSTEM" FOR "DEVELOPING AN UNDERSTANDING OF THE EARTH AS A COMPLETE DYNAMIC SYSTEM." THE PROPOSED STUDY WILL HELP "LEAD TO AN IMPROVED UNDERSTANDING AND REPRESENTATION OF THE INTERACTIONS BETWEEN DIFFERENT EARTH SYSTEM COMPONENTS - SUCH AS LAND-ATMOSPHERE . OR THE INTERACTION OF THE CRYOSPHERE WITH OTHER COMPONENTS."