Droughts and Deluges in Semiarid Grassland Ecosystems: Implications of Co-Occurring Extremes for Carbon Cycling


Melinda D. Smith1* ([email protected]), Anping Chen1, Daniela F. Cusack2, Alan K. Knapp1, Andrew J. Felton3, David L. Hoover4, Seth M. Munson5, Anthony P. Walker6


1Department of Biology, Colorado State University, Fort Collins, CO; 2Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, CO; 3Department of Land Resources and Environmental Sciences, Montana State University–Bozeman, MT; 4Crops Research Laboratory, USDA-ARS, Fort Collins, CO; 5Southwest Biological Science Center, U.S. Geological Survey, Flagstaff, AZ; 6Oak Ridge National Laboratory, Oak Ridge, TN


The overall research project goal is to assess how co-occurring drought and deluge climate extremes will impact key carbon (C)-cycling processes known to be important for carbon-climate feedbacks. The team will address this goal via research in the 280,000 km2 semiarid shortgrass steppe ecoregion located at the western edge of the U.S. Great Plains. Semiarid regions such as this one respond strongly to precipitation extremes and play a dominant role in interannual variability of the global land carbon dioxide sink. The key hypothesis being tested is that when a compound climate perturbation of an extreme deluge occurs within the backdrop of extreme drought, a combination of conditions converge (e.g., warm temperatures, abundant soil moisture, and increased soil nitrogen availability) to strongly stimulate C-cycle processes, potentially resulting in “hot moments” or landscape-level “hot spots” (i.e., increases in biogeochemical processes in time or space that far exceed background levels). To test this hypothesis, researchers are planning to conduct a field experiment designed to quantify the magnitude of C-cycling responses to drought and deluge events (independently and combined) and identify the underlying mechanisms resulting in positive drought-deluge interactions that can lead to hot moments of C cycling. Both above- and belowground C-cycle responses to climate extremes will be quantified during this 3-year experiment. To scale up from the plot-level experiment to the shortgrass steppe ecoregion, the team will use historical climate data to quantify the regional frequency of potential drought-deluge interactions and remote sensing products (e.g., normalized difference vegetation index and solar-induced fluorescence) to estimate C-cycling sensitivity to droughts, deluges, and their combined effects and to identify hot spots in C cycling regionally. Concurrent with these research activities, extreme drought, deluge, and drought-deluge perturbations will be simulated with DOE’s E3SM Land Model (ELM). Researchers will explicitly compare the experimental results and remotely sensed observations of drought-deluge compound climate perturbations to ELM simulations, with the expectation that the process-level understanding gained from field experiment and remote sensing analyses can be used to constrain process representation and parameterization in ELM and to improve Earth system projections of ecosystem C-cycling responses to droughts and deluges at the ecoregion scale.