Alaska Climate Changes in Dynamically Downscaled CMIP5 Simulations

Global models are the most widely used tools for the understanding and assessing of climatic variability and changes. However, coarse resolution limits their capability to capture detailed finer-scale meteorological features, including heterogeneous spatial distributions and high-frequency temporal variability. In this study, the mesoscale Weather Research and Forecasting (WRF) model is used to dynamically downscale the CMIP5/IPCC AR5 global simulation (CCSM MOAR outputs) for a portion of the Arctic marginal zone, encompassing Alaska and surrounding areas (Figure 1), with the aim to improve the understanding, representation, and future projection of high-resolution climate changes in the area. Dynamic downscaling of the 20th century simulation was conducted for the period 1970–2005 and validated against in situ observations archived by the NCDC. Downscaled results generally capture observed conditions well. However, cold biases exist across most of the study area, except for a weak warm bias along the western and northern Alaskan coasts. In addition, downscaled winds are stronger than the observations and precipitation is overestimated along the Alaskan panhandle. The biases in the downscaled temperature, wind speed, and precipitation are correctable, and the downscaled temperature biases exhibit a strong seasonality, with warm biases in the cold months and cold biases in the warm months, particularly along the western and northern Alaskan coasts. The seasonality in the wind speed and precipitation biases, however, is relatively small. Under the RCP6.0 scenario, downscaled regional climate over Alaska and the surrounding areas demonstrates a significant warming trend over the entire study area, with the strongest warming occurring over the Arctic Ocean. Precipitation is also enhanced along Alaska's coastal areas and over the Arctic Ocean. Interior Alaska, on the other hand, becomes drier in the future climate scenario.