Heat Waves in the United States: Definitions, Patterns, and Trends

by Tim Storer

Heat waves have impacts on a variety of industries and demographics throughout the world, and they are much scientific interest. In the United States, research has been done to study the trends in heat wave intensity and frequency. Unfortunately for the researchers, there have traditionally been many varying definitions of “heat waves,” in previous research, and additional work was required to standardize the data so that it could be analyzed for trends. The varying definitions are due to a multitude of interested parties, such as health researchers measuring heat waves that break a dangerous threshold, versus climate scientists tracking temperatures that are in high percentiles. Having compiled all the different definitions, the recent research showed mostly positive trends in the number of heat wave days per year in most of the United States, with the strongest increases in the Southeast and Great Plains regions (Smith et al. 2013). This approach is especially powerful, because by combining many different measures of heat waves, the study is likely to eliminate oversight that any individual measure may have. Continue reading

Heat Stress and Low Humidity with Climate Change will be Hard on Midwestern Corn Crops


by Christina Whalen and Emil Morhardt

Maize (corn) production continues to be a very important source of food, feed, and fuel all around the world, but climate change has raised the concern about being able to maintain the yield rates. A negative relationship between extremely high temperatures (above 30˚C) and yield has already been observed in various regions. Previous studies have not been able to demonstrate which mechanism causes the correlation between extreme temperatures and yield, thus it is possible that the relationship reflects the influence of another variable, such as precipitation rates. There are other possible explanations for the observed relationships. This study explores the mechanisms used in other studies that document the importance of extreme heat on rainfed maize using the process-based Agricultural Production Systems Simulator (APSIM). The study asks three main questions: can APSIM reproduce the empirical relationships—what farmers are seeing on the ground?; if so, what does APSIM imply are the key processes that give rise to these relationships?; how much are these relationships affected by changes in atmospheric CO2? Continue reading