A Comparison of Methods for Simulating Agricultural Evapo-transpiration and Crop Yields under Changing Climate Conditions

Project ID: 5431
Principal Investigator: Michael Tansey
Research Topic: Water Operation Models and Decision Support Systems
Priority Area Assignments: 2012 (Climate Change and Variability Research)
Funded Fiscal Years: 2012
Keywords: climate change, carbon dioxide, evapotranspiration, crop yields

Research Question

The Research and Development (R&D) program in collaboration with other Federal agencies has identified knowledge gaps and research priorities for climate change assessment and adaptation planning. This proposal addresses certain aspects of several of these priority gaps including:

1. Understanding how climate change should impact potential evapo-transpiration and how it is represented in watershed hydrologic models. Gap - 4.02 WH; Priority - High

2. Understanding how climate and/or carbon dioxide changes should impact land cover communities that control natural evapo-transpiration and soil erosion potential. Gap - 4.09 LC; Priority - Medium

3. Understanding how climate change and carbon dioxide changes should impact plant physiology, how impacts vary by crop type, and how impacts affect irrigation demand. Gap - 4.11 LC; Priority - Medium

Specifically, this project will examine various approaches for representing relationships between plant physiological processes and meteorological factors including carbon dioxide in models simulating soil evaporation, plant transpiration, growth, and yield of major agricultural crops. Native and outdoor urban landscape vegetation will also be included to the maximum extent possible within the constraints of time and budget.

Need and Benefit

Climate change will be one of the major challenges affecting the sustainability of Bureau of Reclamation (Reclamation) projects in the 21st century. In Reclamation's recently released "Secure Water Act Section 9503(C) - Reclamation Climate Change and Water 2011" report, a consistent, detailed analysis of the effects of potential climate changes on water supplies for major Reclamation basins was performed. However, water demands could not be similarly analyzed. As stated in the report, "potential climate changes to agricultural, municipal and industrial, and instream water demands are difficult to project; and existing information on the subject is limited." For Reclamation, agricultural and outdoor urban water deliveries constitute a large majority of water demands. The report also states that "water demands will change due to increased air temperatures; increased atmospheric carbon dioxide levels; and changes in precipitation, winds, humidity, atmospheric aerosols, and ozone levels." Other agricultural demand factors mentioned in the report include changes in planting dates, growing season length, crop types, weed and insect populations, as well as socioeconomic conditions. Another important factor will be changes in crop yields, which along with available water supplies, irrigation water requirements, production costs, and market prices, influence agricultural decisions relative to the types and acreages of crop actually planted and harvested. All of these factors affect actual water demands and ultimately the profitability and sustainability of Reclamation projects.

As climate change occurs, Reclamation's water users will need to develop and implement effective adaptation strategies. Already, Reclamation has begun addressing these needs through its West-Wide Climate Risk Assessment and Basin Studies programs. In both instances, as well as for other long-term planning studies, the need for better information on agricultural water demands has been identified as an important need.

This research proposal addresses these gaps by providing a comprehensive review of previous studies and an assessment of existing methods and models for quantifying the effects of climate change on agricultural water demands. The review component will include a thorough review of existing scientific literature on data, methods and models used for computing evapo-transpiration, growth, and yield of major crops grown in the western U.S.. A special emphasis will be given to the effects of CO(v2) as uncertainties associated with its importance have been expressed in some studies. The results of the literature review and database development will directly benefit Reclamation programs by providing a comprehensive reference of data, methods, and models that can be used for climate change studies.

Based on the review, a comparison of methods will be performed by using existing, well- documented models to assess model skill under historic conditions and to evaluate the significance of differences between the models within and between Reclamation regions. Future climate projections will be simulated to establish mean changes in major crop water demands and yields in each Reclamation region during the early, mid, and late 21st century . In addition to the future agricultural water demand and yield data being directly beneficial to regional long-range planning and adaptation studies, the inter-basin comparisons will provide useful insights into the sensitivity of future water demands to various climatic factors. Sensitivity to CO(v2) changes will become apparent from its changes during the 21st century. The overall results of the study will also be useful to Reclamation and others by helping to identify and prioritize needs for future research on the gaps addressed by this study.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Research products developed from this project will include 4 technical reports documenting results from the literature review and parameter database development; model skill assessment and inter-comparisons under historic climate conditions by and between regions for major crops; model comparisons under projected future climate and carbon dioxide conditions by and between regions for major crops; and a Final Technical report describing the study assumptions, models, methods and results comparisons. In addition, the project team will make multiple presentations at various workshops and scientific conferences to disseminate the results and improve understanding of the priority gap areas. At least one manuscript for publication in peer journal will be prepared and submitted.

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Last Updated: 4/4/17