WATER ALLOCATION INSTITUTIONS ARE FUNDAMENTAL TO AGRICULTURAL PRODUCTION IN THE ARID WESTERN US, WHERE PRECIPITATION DURING GROWING SEASONS IS NEGLIGIBLE, SURFACE AND GROUNDWATER SOURCES ACCOUNT FOR OVER 90% OF AGRICULTURAL WATER USE, AND WATER RIGHTS ARE FULLY ALLOCATED. MOUNTAIN SNOWPACK, A SIGNIFICANT SOURCE OF THE REGION'S WATER, PROVIDES NATURAL STORAGE AND CONTROLLED WATER RELEASE TIMING. BUILT WATER STORAGE AND DELIVERY INFRASTRUCTURE EVOLVED WITH THE EXPECTATION OF UNCHANGED MOUNTAIN SNOWMELT-TIMING PATTERNS. BUT THOSE PATTERNS NO LONGER REPRESENT CURRENT AND FUTURE SNOWPACK PATTERNS. IN PARTICULAR, CHANGES IN RUNOFF TIMING AND AMOUNTS POSE CHALLENGES FOR AGRICULTURAL WATER RIGHTS HOLDERS. PEAK FLOWS FROM MELTING SNOW THAT OCCUR TOO EARLY TO USE IN AGRICULTURAL PRODUCTION INCREASE ECONOMIC RISKS TO AGRICULTURE. IT HAS BEEN DEMONSTRATED THAT EARLIER SNOWMELT CAN GENERATE LESS AVAILABLE WATER FOR AGRICULTURAL PRODUCERS WITH SENIOR WATER RIGHTS, AND MORE AVAILABLE WATER FOR JUNIOR NON-AGRICULTURAL WATER RIGHTS HOLDERS. WHILE TRENDS INDICATE EARLIER PEAK FLOWS, THEY ALSO SUGGEST INCREASED VARIABILITY MEDIATED BY LOCAL CLIMATE AND TOPOGRAPHY. IMPACTS ARE NOT LIMITED TO GREATER YEAR-TO-YEAR VARIATION IN YIELDS AND INCOME; INCREASED RISK ALSO INFLUENCES PRIVATE DECISIONS TO SELL IRRIGATION WATER RIGHTS AND LANDS, CAUSING PERMANENT LOSSES IN THE CAPACITY FOR FOOD PRODUCTION IN THE ARID WEST. DECISION-MAKING CAN BE IMPROVED WITH A BETTER UNDERSTANDING OF HOW CHANGES IN WATER FLOWS INFLUENCE AGRICULTURAL PRODUCER DECISION-MAKING, AND HOW WATER INSTITUTIONS CAN EXACERBATE OR RELIEVE CONSTRAINTS FROM THESE CHANGES.WATER POLICY ANALYSTS PREDICT THAT WATER MANAGEMENT IN THE WESTERN US WILL UNDERGO EXTENSIVE CHANGES TO ADAPT TO MOUNTAIN SNOW MELT PATTERNS, WITH A FOCUS ON WATER ALLOCATION INSTITUTIONS. IN RESPONSE TO RECENT CONFLICTS, WHERE EXISTING WATER ALLOCATION INSTITUTIONS HAVE FAILED TO ALLOCATE WATER IN ACCORDANCE WITH ALL RIGHTS HOLDERS' EXPECTATIONS, STATES HAVE EXERCISED THEIR RIGHTS TO INTERVENE TO LIMIT PERMITTED WATER RIGHTS. THE PROSPECT OF MORE INSTANCES OF STATE INTERVENTION TO RESOLVE CONFLICT HAS GENERATED INTEREST IN WHETHER AND HOW TO MODIFY WATER INSTITUTIONS TO PERFORM BETTER WITH CHANGING CONDITIONS. YET, THERE ARE FEW EMPIRICAL STUDIES OF THE IMPLICATIONS OF CHANGING MOUNTAIN SNOWPACK AND SNOWMELT TIMING ON WATER AVAILABLE FOR AGRICULTURE, AND OF THE ABILITY OF WATER INSTITUTIONS TO MANAGE ECONOMIC IMPACTS ON AGRICULTURE AND FOOD PRODUCTION. MODIFICATIONS TO WATER ALLOCATION INSTITUTIONS MAY HASTEN THE RATE AT WHICH LANDS PERMANENTLY TRANSITION OUT OF AGRICULTURE, AND COULD GENERATE NEGATIVE IMPACTS TO AGRICULTURAL PRODUCERS WHO CURRENTLY HOLD MORE VALUABLE SENIOR RIGHTS, WHILE FAVORING NON-AGRICULTURAL JUNIOR RIGHTS HOLDERS. ALTERNATIVELY, INFLEXIBLE INSTITUTIONS COULD RESULT IN RIGHTS HOLDERS' WASTING WATER OR BEING RELUCTANT TO ADOPT CONSERVATION TECHNOLOGY TO AVOID RISK OF LOSING WATER RIGHTS.MORE EMPIRICAL INFORMATION IS NEEDED REGARDING HOW CHANGES IN MOUNTAIN SNOWPACK WILL AFFECT AVAILABLE WATER; WHICH BASINS IN THE ARID WEST ARE MOST AT RISK; THE EFFECTIVENESS OF EXISTING WATER ALLOCATION INSTITUTIONS IN MANAGING THESE CHANGES, IN COMPARISON WITH PROPOSED MODIFICATIONS OF WATER RIGHTS INSTITUTIONS; AND HOW CHANGES IN AVAILABLE WATER AND INSTITUTIONAL RESPONSES AFFECT THE DISTRIBUTION OF ECONOMIC WELL-BEING OF GROUPS IN SOCIETY, INCLUDING THE SUSTAINABILITY OF AGRICULTURAL PRODUCTION IN THE ARID WEST. THIS INFORMATION IS ESSENTIAL TO 3 SETS OF DECISION-MAKERS: REGIONAL, STATE AND FEDERAL WATER POLICYMAKERS WHOSE INTERESTS ARE THE DESIGN OF POLICIES AND INSTITUTIONS TO IMPROVE EFFICIENCY OF WATER ALLOCATION AND NET BENEFITS TO SOCIETY; LOCAL WATER DISTRICT MANAGERS AS THEY DETERMINE IN THE SHORT RUN, AND ACCORDING TO THE INSTITUTIONS AND RULES SET FORTH BY POLICY, WHERE AND WHEN TO DIVERT WATER FLOWS FROM THE VARIOUS SOURCES THROUGH THEIR SYSTEMS TO END USERS, IN RESPONSE TO VARIATIONS IN THOSE SOURCES; AND INDIVIDUAL AGRICULTURAL PRODUCERS AND OTHER WATER RIGHTS HOLDERS IN DECIDING HOW THEY WILL USE WATER AS A PRODUCTIVE INPUT AND HOW THEY WILL RESPOND TO CHANGES IN THE ASSET VALUE OF THEIR WATER RIGHTS. TO BE OF VALUE TO DECISION-MAKERS, EMPIRICAL INFORMATION MUST BE PROVIDED IN A MANNER THAT SPECIFICALLY ADDRESSES THE DECISION PROBLEMS AT HAND. THIS MEANS THAT TIMING, FORMAT, UNITS OF MEASUREMENT, ACCESSIBILITY, AND OTHER ATTRIBUTES OF EMPIRICAL INFORMATION NEED TO BE DESIGNED TO BE OF PRACTICAL USE TO IMPROVE DECISION-MAKING OUTCOMES, USING A COMMON CORE OF INFORMATION PRODUCTS.FINALLY, MORE INFORMATION IS NEEDED REGARDING CRITERIA FOR SUCCESSFUL GOVERNANCE REGARDING CHANGES IN RESOURCE ENDOWMENTS. DECISION-MAKING PROCESSES REGARDING PROPOSED CHANGES TO WATER ALLOCATION INSTITUTIONS, RIGHTS STRUCTURES, AND POLICIES MUST ACKNOWLEDGE POWER DISPARITIES THAT MAY EXIST AMONG DIVERGENT AND COMPETING DEMANDS FOR LIMITED WATER SUPPLIES, ALLOW THE VARIOUS STAKEHOLDERS TO EXPRESS THEIR INTERESTS, AND ADDRESS BOTH DIRECT AND INDIRECT DISTRIBUTIONAL IMPLICATIONS OF PROPOSED POLICY CHANGES, WHILE LEADING TO MULTILATERALLY AGREEABLE OUTCOMES.WITH A TEAM OF 11 RESEARCHERS FROM 5 INSTITUTIONS IN 3 STATES REPRESENTING SEVERAL ACADEMIC DISCIPLINES, THIS PROJECT USES ECONOMICS AS THE BASIC APPROACH TO IDENTIFY HOW CHANGES IN MOUNTAIN SNOWPACK AFFECT WATER ALLOCATION AND AGRICULTURE IN THE ARID WEST, THE DECISION-MAKERS WHO MUST ADDRESS THESE PROBLEMS, AND THE NATURE AND FORMAT OF INFORMATION NEEDED FOR DECISION-MAKING REGARDING WATER ALLOCATION TO TAKE INTO ACCOUNT DIRECT AND INDIRECT IMPACTS AND DIVERSE INTERESTS. THIS APPROACH UNIFIES PROJECT COMPONENTS, AND PROVIDES A PERSPECTIVE THAT GOES BEYOND THE PRIMARY END-USERS OF THE SCIENCE, PLACING IT IN THE CONTEXT OF THE LARGER COMMUNITY. METHODS USED TO COLLECT DATA, PERFORM ANALYSES AND INFORM TARGET AUDIENCES INCLUDE:IN COLLABORATION WITH THE NATIONAL CENTER FOR ATMOSPHERIC RESEARCH, MODIFY THE NATIONAL WATER MODEL(NWM) TO PREDICT AMOUNT, TIMING, AND FLOW RATES OF SURFACE WATER AS AFFECTED BY CHANGES IN MOUNTAIN SNOWPACK;GENERATE CLIMATE SCENARIOS TO REPRESENT PROJECTED SHIFTS, AS INPUTS TO THE NWM;USE NWM OUTPUTS AS INPUTS TO LOCAL WATER DISTRICT-LEVEL ALLOCATION MODELS, INCORPORATING ALTERNATIVE WATER INSTITUTIONS;DEVELOP AN ECONOMIC SIMULATION MODEL USING OUTPUT FROM THE NWM TO PREDICT CHANGES IN THE USES AND VALUE OF WATER, AS AFFECTED BY CHANGES IN SNOWPACK AND ALLOCATIVE INSTITUTIONS;DEVELOP ECONOMETRIC MODEL OF THE ECONOMIC VALUE OF SENIORITY OF APPROPRIATIVE WATER RIGHTS, USING DATA FROM CASE STUDY BASINS;EVALUATE WATER INSTITUTIONS USING ECONOMIC EFFICIENCY AND DISTRIBUTIONAL CRITERIA;CONDUCT STAKEHOLDER ANALYSES TO IDENTIFY PARTICIPANTS FOR A TECHNICAL ADVISORY GROUP (TAG), WHICH WILL COLLABORATE WITH SCIENTISTS THROUGHOUT THE PROJECT;GENERATE WATER FOOTPRINTS FOR CASE STUDY BASINS IN NEVADA, COLORADO AND ARIZONA;EVALUATE OUTCOMES FROM ECONOMIC MODELS USING ALTERNATIVE WATER ALLOCATION INSTITUTIONS AND NWM OUTPUTS, INCORPORATING TAG PARTICIPATION;CONDUCT EVALUATION OF WATER ALLOCATION GOVERNANCE WITH TAG PARTICIPATION;DEVELOP AND DISSEMINATE EXTENSION OUTREACH PRODUCTS;CONDUCT EXTERNAL PROJECT EVALUATION THROUGHOUT PROJECT, INCORPORATING FEEDBACK.THE PROJECT'S GOALS ARE TO DEVELOP AND APPLY REPLICABLE METHODS FOR ANTICIPATING MOUNTAIN SNOWPACK CHANGES, EVALUATE THE ABILITY OF WATER INSTITUTIONS TO RESPOND TO THESE CHANGES, ASSESS SHORT AND LONG RUN IMPACTS ON AGRICULTURE AND FOOD PRODUCTION, AND DESIGN A COLLABORATIVE FRAMEWORK TO ENHANCE PARTICIPATION OF DIVERSE INTERESTS TO ADDRESS THESE CHANGES. GENERAL IMPACTS OF MEETING THESE GOALS WILL BE IMPROVED ABILITY TO ADAPT TO FLUCTUATIONS IN MOUNTAIN SNOWPACK WATER AVAILABILITY TO MANAGE AGRICULTURAL RISK, AND IMPROVED INDIVIDUAL AND COLLECTIVE POLICY DECISION-MAKING CONCERNING WATER ALLOCATION AND AGRICULTURE IN THE ARID WESTERN STATES AND ELSEWHERE, LEADING TO MORE RESILIENT FOOD SYSTEMS.