EPS Colloquium – Xuhui Lee, Yale University
Climatic effects of local land cover and land use change
Land cover on the Earth’s surface typically varies at spatial scales smaller than the grid size of a climate model. Similarly, contemporary land use activities, such as urbanization and deforestation, are occurring at local scales than cannot be resolved by climate models. Heterogeneity in land cover causes spatial variability in climate, and land use changes can perturb local climate conditions more than the change signals associated with greenhouse gases. A good understanding of these two classes of “sub-grid” problem is helpful to inform climate adaptation efforts and efforts to improve the land parameterization in climate models.
In this study, the climate effect of local land use change is quantified as a linear addition of an indirect component and a direct component. The indirect component represents the signal arising from regional atmospheric feedback. The direct component can be evaluated with a “space-for-time” substitution, using simultaneous observations made at two adjacent land cover types and data produced by a climate model at sub-grid tiles within the same model grid. This framework is applied to two cases. In Case I, the local climate effect associated with historical deforestation is investigated with an ensemble of five LUMIP (Land-Use Model Intercomparison Project) models. In Case II, the humid heat burden due to urbanization is quantified with observations at paired urban and rural weather stations and with sub-grid data generated by NCAR’s Earth System Model. Results show that the direct effect of local land use is more predictable than the indirect effect, the latter of which may be masked by internal climate variability.
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Professor Lee’s research and teaching concern the interactions between the terrestrial biosphere, the atmosphere and anthropogenic drivers. His areas of interest include boundary-layer meteorology, micrometeorological instrumentation, remote sensing, and carbon cycle science. One focus of his research activity is on biophysical effects of land use on the climate system. Other ongoing projects investigate greenhouse gas fluxes in the terrestrial environment (forests, cropland and lakes), isotopic tracers in the cycling of carbon dioxide and water vapor, and urban climate adaptation and mitigation. His lab group deploys an array of research methodologies, including field observations (eddy covariance, optical isotope instruments, and high-precision greenhouse gas analyzers), mathematical models (land surface models, large-eddy simulation, WRF, and earth system models), and environmental remote sensing (satellites and drones). He is Sara Shallenberger Brown Professor of Meteorology and Director of the Yale Center for Earth Observation. His recent textbook Fundamentals of Boundary-Layer Meteorology offers the accumulation of insights gained during his academic career as a researcher and teacher in the field of boundary-layer meteorology.