Introduction

Ecophysiological models were the dominant tools used to estimate the potential impact of climate change in agroecosystems in the Third and Fourth Assessment Reports of the IPCC (Gitay et al. 2001; Easterling et al. 2007) and are widely used elsewhere in climate change research. These models, also known as "crop models" or "simulation models", attempt to encapsulate the best-available knowledge on plant physiology, agronomy, soil science and agrometeorology in order to predict how a

US Arid Land Agricultural Research Center, USDA-ARS, 21881 North Cardon Lane,

Maricopa, AZ 85224

email: [email protected]

G. Hoogenboom

Biological and Agricultural Engineering, 165 Gordon Futral Court, The University of Georgia, Griffin, GA 30223-1731 email: [email protected]

D. Lobell and M. Burke (eds.), Climate Change and Food Security, 59

Advances in Global Change Research 37, DOI 10.1007/978-90-481-2953-9_4, © Springer Science + Business Media, B.V. 2010

plant will grow under specific environmental conditions. The models are "ecophysi-ological" because they use mathematical descriptions of physiological, chemical and physical processes to simulate crop growth and development over time. Physiological processes considered may include photosynthesis, respiration, growth and partitioning, development of reproductive structures, transpiration, and uptake of water and nutrients. Chemical and physical processes can involve soil chemical transformations, energy flows, and diffusion of gases into and out of leaves, among others.

To predict crop growth, the model requires that initial conditions be specified, such as the soil nutrient and water status, the planting date and density. Data on temperature, solar radiation, precipitation, or other weather parameters are then used to estimate how the development and growth of the crop progress over the cropping season. Most models operate at daily time steps, starting at planting and ending at the prediction of harvest or physiological maturity, depending on the crop. Information on irrigations, fertilizer applications, tillage events, pests, diseases, or other factors also may be considered.

The first ecophysiological models were developed by De Wit (1965) in the Netherlands and Duncan and colleagues in the United States (Duncan et al. 1967). These models were primarily used as research platforms to quantitatively test basic hypotheses about plant growth and development (Loomis et al. 1979). As computing power increased and understanding of basic processes improved, more factors were considered, such as the dynamics of specific nutrients in the soil and plant and the effects of pests and diseases.

Models are available for all major annual crops and many minor crops (e.g., Jones et al. 2003). Current models typically run on a personal computer or a work station and can simulate a cropping season in less than 1 s. The responsiveness of the models to climate and other environmental variables, as well as to crop management, allow them to be easily adapted to simulate responses to projected climate conditions, such as obtained from general circulation models.

This chapter first reviews how ecophysiological models function with emphasis on the physiological responses that are most relevant to climate change research. We then discuss how the models are applied in climate change research and identify challenges and opportunities for improving the models per se and how they are applied to climate change research. The overall objective is to help readers understand how the features of ecophysiological models affect projections of potential impacts of climate change. Readers seeking further information should consult texts such as Hay and Porter (2006) for an overview of the physiological assumptions and Tsuji et al. (1998) or Hanks and Ritchie (1991) for details on modeling both plant and soil processes.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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