High-resolution climate change mapping with gridded historical climate products

The detection of climate-driven changes in coupled human-natural systems has become a focus of climate research and adaptation efforts around the world. High-resolution gridded historical climate (GHC) products enable analysis of recent climatic changes at the local/regional scales most relevant for research and decision-making, but these fine-scale climate datasets have several caveats. We analyzed two 4 km GHC products to produce high-resolution temperature trend maps for the US Northeast from 1980 to 2009, and compared outputs between products and with an independent climate record. The two products had similar spatial climatologies for mean temperatures, agreed on temporal variability in regionally averaged trends, and agreed that warming has been greater for minimum versus maximum temperatures. Trend maps were highly heterogeneous, i.e., a patchy landscape of warming, cooling and stability that varied by month, but with local-scale anomalies persistent across months (e.g., cooling 'pockets' within warming zones). In comparing trend maps between GHC products, we found large local-scale disparities at high elevations and along coastlines; and where weather stations were sparse, a single-station disparity in input data resulted in a large zone of trend map disagreement between products. Preliminary cross-validation with an independent climate record indicated substantial and complex errors for both products. Our analysis provided novel landscape-scale insights on climate change in the US Northeast, but raised questions about scale and sources of uncertainty in high-resolution GHC products and differences among the many products available. Given rapid growth in their use, we recommend exercising caution in the analysis and interpretation of high-resolution climate maps.