ALTHOUGH ULTRAVIOLET (UV) RADIATION REPRESENTS ONLY SMALL FRACTION OF THE SOLAR RADIATION REACHING THE EARTH'S SURFACE, THE IMPACTS OF UV ON THE BIOSPHERE ARE SIGNIFICANT. STRATOSPHERIC OZONE IS ONE OF THE MAIN ABSORBERS OF THE UV PORTION OF THE SOLAR SPECTRUM. MEASUREMENTS IN THE MID-TO-LATE TWENTIETH CENTURY SHOWED SIGNIFICANT STRATOSPHERIC OZONE DEPLETION, WITH CORRESPONDING INCREASES IN SURFACE UV RADIATION, OVER POLAR REGIONS RESULTING FROM EMISSIONS OF OZONE-DEPLETING COMPOUNDS. THIS DISCOVERY PROMPTED A SWIFT INTERNATIONAL EFFORT TO PHASE OUT THESE SUBSTANCES, AN ACTION THAT HAS RESULTED IN THE NEAR-COMPLETE RECOVERY OF THE OZONE LAYER. HOWEVER, RECENT OBSERVATIONS OF NEW EMISSIONS OF CERTAIN OZONE-DEPLETING COMPOUNDS INTRODUCE UNCERTAINTY IN PROJECTIONS OF STRATOSPHERIC OZONE AND THEREFORE SURFACE UV RADIATION. FURTHER, COMPLEX INTERACTIONS BETWEEN CLIMATE CHANGE AND UV-B LEVELS ARE STILL NOT WELL UNDERSTOOD AND MAY HAVE IMPLICATIONS FOR FUTURE SURFACE UV LEVELS.RESPONDING TO THESE CONCERNS IN OCTOBER 1992, THE USDA FUNDED THE UV-B MONITORING AND RESEARCH PROGRAM (UVMRP) TO MONITOR UV-B LEVELS OVER WIDE GEOGRAPHIC AREAS OF THE U.S. AND TO ASSESS THE IMPACT OF UV RADIATION ON CROPS AND ECOSYSTEMS. MORE RECENTLY, THE UVMRP ADDED A THIRD COMPLEMENTARY OBJECTIVE TO DEVELOP A COMPREHENSIVE COMPUTATIONAL MODEL THAT WILL BE ABLE TO EVALUATE THE LONG-TERM EFFECTS OF CLIMATE CHANGE, UV EXPOSURE, AND THEIR INTERACTIVE EFFECTS, WITH A FOCUS ON THE ECONOMIC IMPACTS OF THESE ENVIRONMENTAL STRESSORS. TO ADDRESS THESE OBJECTIVES, THE UVMRP PURSUES RESEARCH IN THREE PROGRAM AREAS:CLIMATOLOGY DATA COLLECTION: THE UVMRP HAS ESTABLISHED A 41-STATION CLIMATOLOGICAL AND RESEARCH NETWORK THAT COVERS A WIDE RANGE OF ECOREGIONS, ELEVATIONS AND LAND-USE TYPES, INCLUDING A MIX OF CROP, FOREST AND RANGELANDS. EACH CLIMATOLOGICAL NETWORK STATION IS EQUIPPED WITH INSTRUMENTS CAPABLE OF MEASURING ULTRAVIOLET AND VISIBLE SOLAR RADIATION. RAW INSTRUMENT SIGNALS ARE EXAMINED FOR QUALITY CONTROL (QC) ISSUES AND ADJUSTED USING CALIBRATION FACTORS TO PRODUCE HIGH-QUALITY SOLAR IRRADIANCE DATA. IRRADIANCE DATA ARE SUBSEQUENTLY USED AS INPUTS TO WELL-ESTABLISHED ALGORITHMS TO CALCULATE A SERIES OF RELEVANT DERIVED PRODUCTS (E.G., UV INDEX, BIOLOGICALLY-WEIGHTED SUMS). THE IRRADIANCE DATA AS WELL AS THE DERIVED PRODUCTS ARE MADE AVAILABLE ON THE UVMRP WEBSITE WITHIN 48 HOURS OF COLLECTION (HTTP://UVB.NREL.COLOSTATE.EDU). THE UVMRP STAFF, ASSISTED BY LOCAL SITE OPERATORS, PERFORM ROUTINE ON-SITE MAINTENANCE AND TROUBLESHOOT OCCASIONAL INSTRUMENT MALFUNCTIONS TO MAINTAIN AT LEAST 95% DATA RETRIEVAL RATES OVER THE ENTIRE NETWORK. IN ADDITION, UVMRP CONTINUALLY INVESTIGATES NEW CALIBRATION AND QC PROCEDURES TO IMPROVE DATA QUALITY AND BETTER MEET THE NEEDS OF OUR STAKEHOLDERS. UVMRP RESEARCHERS ALSO CONDUCT ANALYSES USING NETWORK DATA TO EXPAND OUR DERIVED PRODUCTS AND CONTRIBUTE TO OUR UNDERSTANDING OF THE TRENDS IN SURFACE UV RADIATION.EFFECTS RESEARCH: BY USING COMPUTER-CONTROLLED-CROP-GROWTH CHAMBERS, THE UVMRP AND ITS COLLABORATORS RECORD, ANALYZE, AND QUANTIFY CROP RESPONSES TO THE ISOLATED AND INTERACTIVE EFFECTS OF ENVIRONMENTAL STRESS FACTORS (E.G., DROUGHT, UV-B RADIATION). THESE RESULTS HELP IDENTIFY PLANT CHARACTERISTICS THAT COULD BE MANIPULATED BY PLANT BREEDERS TO DEVELOP CULTIVARS THAT CAN TOLERATE EXTREME AND VARIABLE ENVIRONMENTAL CONDITIONS. FURTHER, CHAMBER EXPERIMENTS INFORM THE DEVELOPMENT OF FUNCTIONAL ALGORITHMS THAT DESCRIBE CROP RESPONSE TO UV-B AND OTHER ENVIRONMENTAL STRESS FACTORS THAT CAN BE INCORPORATED INTO CLIMATE-CROP MODELS. THE WORK PROPOSED HERE WILL EXPAND OUR ANALYSES TO RICE, WITH A FOCUS ON THE IMPACT OF DROUGHT AND EXTREME TEMPERATURES ON BOTH ABOVE (LEAF, STEM) AND BELOW (ROOT) GROUND PLANT MORPHOLOGY.INTEGRATED ASSESSMENT: THE AGRICULTURAL COMMUNITY AND DECISION MAKERS REQUIRE RELIABLE CROP YIELD ASSESSMENT TOOLS TO DETERMINE OPTIMAL MANAGEMENT PRACTICES, ASSESS RISKS AND RISK MANAGEMENT STRATEGIES, AND DEFINE ECONOMIC IMPACTS. THE UVMRP IS WORKING WITH COLLABORATORS TO DEVELOP A COMPREHENSIVE COMPUTATIONAL MODEL THAT WILL COUPLE STATE-OF-THE-ART CLIMATE, CROP AND BIOGEOCHEMICAL MODELS TO STUDY THE INFLUENCE OF ENVIRONMENTAL CHANGE ON ECOSYSTEMS AND AGRICULTURAL PRODUCTIVITY, AND THE RESULTING ECONOMIC IMPACTS OF THESE INTERACTIONS. MODULES FOR CORN AND SOYBEAN ARE UNDER DEVELOPMENT AND PRELIMINARY RESULTS SHOW PROMISING AGREEMENT BETWEEN MODELED AND MEASURED DATA IN THE U.S.