This Friedman Seminar features Nathan Mueller, Postdoctoral Fellow at Harvard University in the Department of Earth and Planetary Sciences and the Department of Organismic and Evolutionary Biology, presenting "Crop water use and extreme temperatures: Implications for future food production."
High temperature extremes during the growing season can reduce crop productivity. At the same time, agricultural practices can modify temperatures by altering the surface energy balance, either via shifts in surface reflectivity or from how much energy is utilized to evaporate water from the soil surface and from leaves (together termed “evapotranspiration”). Here I investigate summer climate trends in major cropping systems and their relationships with changes in agricultural land management. In the US Midwest, 100-year trends are towards cooler summer temperature extremes and increased precipitation, conditions generally more favorable for agricultural production. Statistically significant associations are found between the cooling pattern and trends in cropland intensification. Greater use of irrigation is also associated with cooling over a small subset of area. Land conversion to cropland, often considered an important influence on historical temperatures, is not significantly related to cooling. I propose that cooling is primarily associated with greater rates of water use (evapotranspiration) from more productive crop vegetation, consistent with greater cooling trends at the highest temperature percentiles and the increase in precipitation. Rainfed and irrigated areas diverge in their response to drought; rainfed areas revert to historically high extreme temperatures during drought, while irrigated areas sustain cooling. I then examine trends in climate and land use from 1961 to present for seven major temperate cropping regions using global historical land use data. Consistent with results for the US, all regions examined with intensification of summer crops experience cooling of temperature extremes proportional to the degree of intensification. I will discuss the implications of these findings for projecting crop yields under climate change.
Nathan Mueller is a Postdoctoral Fellow at Harvard University in the Department of Earth and Planetary Sciences and the Department of Organismic and Evolutionary Biology. His research analyzes the interactions between climate, water resources, and agricultural management to promote global food security and more sustainable agricultural landscapes. He received his Ph.D. from the University of Minnesota in 2013.