To help guide the discussion and illustrate the time series modeling process, we will use a dataset for US maize yields from 1950-2005. The United States Department of Agriculture (USDA) has recorded average yields for each county since early in the twentieth century, and in many cases since the late 1800s. In addition, the United States has arguably the most complete weather records of any country for the twentieth century. Here we have averaged yields over all counties east of the 100° W meridian, which separates mostly irrigated maize in the West from mostly rainfed maize in the East. The average was weighted by the area sown to maize in each county, so that yields in counties with high acreage were proportionally more important. Weather data from individual stations were similarly weighted.
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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.