title: Evaluating the utility of dynamical downscaling in agricultural impacts projections.
abstract: Interest in estimating the potential socioeconomic costs of climate change has led to the increasing use of dynamical downscaling--nested modeling in which regional climate models (RCMs) are driven with general circulation model (GCM) output--to produce fine-spatial-scale climate projections for impacts assessments. We evaluate here whether this computationally intensive approach significantly alters projections of agricultural yield, one of the greatest concerns under climate change. Our results suggest that it does not. We simulate US maize yields under current and future CO2 concentrations with the widely used Decision Support System for Agrotechnology Transfer crop model, driven by a variety of climate inputs including two GCMs, each in turn downscaled by two RCMs. We find that no climate model output can reproduce yields driven by observed climate unless a bias correction is first applied. Once a bias correction is applied, GCM- and RCM-driven US maize yields are essentially indistinguishable in all scenarios (<10% discrepancy, equivalent to error from observations). Although RCMs correct some GCM biases related to fine-scale geographic features, errors in yield are dominated by broad-scale (100s of kilometers) GCM systematic errors that RCMs cannot compensate for. These results support previous suggestions that the benefits for impacts assessments of dynamically downscaling raw GCM output may not be sufficient to justify its computational demands. Progress on fidelity of yield projections may benefit more from continuing efforts to understand and minimize systematic error in underlying climate projections.
authors.affiliation: Department of the Geophysical Sciences and.
authors.forename: Michael
authors.initials: M
authors.lastname: Glotter
authors.affiliation: Computation Institute, University of Chicago, Chicago, IL 60637; and jelliott@ci.uchicago.edu.
authors.forename: Joshua
authors.initials: J
authors.lastname: Elliott
authors.affiliation: Department of the Geophysical Sciences and.
authors.forename: David
authors.initials: D
authors.lastname: McInerney
authors.affiliation: Computation Institute, University of Chicago, Chicago, IL 60637; and.
authors.forename: Neil
authors.initials: N
authors.lastname: Best
authors.affiliation: Computation Institute, University of Chicago, Chicago, IL 60637; andMathematics and Computer Science, Argonne National Laboratory, Lemont, IL 60439.
authors.forename: Ian
authors.initials: I
authors.lastname: Foster
authors.affiliation: Department of the Geophysical Sciences and.
authors.forename: Elisabeth J
authors.initials: EJ
authors.lastname: Moyer
mesh_terms: D000383:Agriculture / Q000379:methods*; D000465:Algorithms; D002245:Carbon Dioxide; D002980:Climate; D057231:Climate Change; D003198:Computer Simulation; D003247:Conservation of Natural Resources; D018556:Crops, Agricultural; D005523:Food Supply; D005544:Forecasting; D005843:Geography; D008962:Models, Theoretical; D009656:North America; D011336:Probability; D015203:Reproducibility of Results; D003313:Zea mays
chemical_list: D002245:Carbon Dioxide
keywords: CORDEX; NARCCAP; agriculture; food security