NSF Award
2304953
The transformation of global agriculture over the last century is rightly called a revolution, as the use of fertilizers, pesticides, irrigation, and hybridization has boosted crop yields by perhaps a factor of three. The increased yields mean that today's croplands are home to the most intense vegetation growth on earth, accompanied by the greatest plant water use on earth. Most of the water taken up by plants is released to the atmosphere through the leaves, thus higher crop yields should be accompanied by increases in atmospheric humidity. Moreover, since thermal energy is expended in converting liquid water into water vapor, increased humidity is typically accompanied by cooling. In the absence of irrigation, atmospheric moistening comes at the expense of soil moisture, as the water vapor released from the leaves is first taken up from the soil by the plant roots. Given these effects on humidity, temperature, and soil moisture, along with the fact that croplands cover about a third of the world's land surface, it is natural to ask what effects the Green Revolution has had on global climate. But such effects are difficult to identify, particularly as they could differ from one region to another.<br/><br/>In this project the Principal Investigators (PIs) examine the effects of agriculture on climate extremes, focusing on three particular types: 1) heat waves and humid heat waves, the latter measured by the wet bulb temperature, 2) flash drought, meaning droughts with sudden onset, and 3) prolonged hot/dry and cool/wet conditions. The PIs examine several hypotheses, one that agricultural intensification increases the risk of flash drought during hot and dry growing seasons. Another is that agriculture reduces the risk of dry heat waves but increases the risk of humid heat waves. A central consideration for the work is that the effects of vegetation on climate extremes are likely to depend on the aridity of the region, as in more arid regions evaporation and transpiration are limited by the amount of moisture in the soil, while in regions of greater water abundance the limiting factor is the amount of energy (sunlight, in particular) available to convert liquid water into water vapor.<br/><br/>The work involves analysis of several datasets including reanalysis products and climatic precipitation datasets, and simulations from the Community Earth System Model (CESM2) including version 5 of the Community Land Model (CLM, version 5), and analysis of simulations from the Land Use Model Intercomparison Project (LUMIP). CLM includes a representation of agricultural land cover and irrigation which can be enabled or disabled to allow comparisons of simulations with and without agricultural effects. The LUMIP archive includes simulations for a historical period (1850 to the present) in which either CO2 or land cover is held fixed, and with farm and pastureland treated explicitly as agricultural land or counterfactually as either unmanaged grassland or as agricultural land with irrigation fixed at 1850 levels.<br/><br/>The work is of societal as well as scientific interest given the impacts of climate extremes on human activities. In addition the project provide support and training to a graduate student and undergraduate work-study students. Students are recruited in collaboration with the Syracuse Office for Undergraduate Research and Creative Engagement (SOURCE) and other organizations dedicated to enhancing the diversity of the science and technology workforce.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
