Simulating Regional Climate Change in New Hampshire

Abstract:

Dynamical downscaling of Global Climate Model (GCM) simulated future projections using smaller scale, higher resolution models is widely used to assess the regional impacts of climate change on weather, ecosystems and economy. In this study, the Weather Research and Forecasting (WRF) model is used to dynamically downscale Community Earth System Model (CESM) future projections using Representative Concentration Pathways (RCP) 4.5 and 8.5 to simulate the possible effects of climate change in New Hampshire (NH). The first step to ensure that the downscaled model output is representative of the NH region is to find the correct WRF model set up for the region. This task is accomplished using CESM simulations of the historical period as forcing for WRF simulations and performing multiple sensitivity tests with different options for WRF physics parameterizations such as boundary layer, cloud microphysics and convection parameterizations. Simulated precipitation, temperature and other variables are compared with observations to obtain the more suitable model setup for NH. WRF simulations are performed on nested grids with 36, 12 and 4 km grid spacing, and the smallest grid sized nest is focused over NH. Furthermore, to prevent the drift of regional model from global model simulated climatology, WRF is reinitialized from GCM output every five days. Previous studies have shown that future regional climate model predictions of precipitation and snow water equivalent depend on the re-initialization interval of WRF from GCM forcing specifically over the western U.S, where topography is high. This problem is mainly because re-initialization erases the simulated memory for certain variables such as soil moisture. To evaluate whether re-initialization time-scale is also important in the Eastern US, in this study, the effects of 5-daily versus monthly re-initialization of WRF using CESM output on model simulated precipitation are also investigated. The obtained WRF model setup is then used to simulate future climate changes in NH using CESM forcing with RCP 4.5 and RCP 8.5. The climatology from these downscaled climate simulations will then be used as forcing in smaller scale ecosystem and economy models to predict the economical value of climate change in the region.