Assessment of climate change impact over California using dynamical downscaling with a bias correction technique: method validation and analyses of summertime results

Abstract

This study explores climate-change influences on future air pollution-relevant meteorological variables (e.g., temperature, wind, humidity, boundary layer heights) and atmospheric phenomena (e.g., heat wave, marine air penetration, droughts) over California by the 2050s. The Community Earth System Model simulation results from Coupled Model Intercomparison Project Phase 5 under an emission scenario that most closely aligns with California's climate change goals were bias-corrected with respect to North American Regional Reanalysis data to reduce biases in both the climatological mean and inter-annual variations. The bias-corrected ~ 1° × 1° meteorological fields were dynamically downscaled to a resolution of 4 km × 4 km over California using the Weather Research and Forecasting model. This study focuses on summertime results, while the analysis of wintertime results will be presented in a separate paper. Our downscaled results projected a future increase of approximately 1 K in summer mean surface temperature over California under this single future climate realization. The temperature increase is larger in the nighttime than in the daytime. Water vapor mixing ratio is also projected to increase over California and off the coast. There are discernable decreases in boundary layer heights over the mountain ranges surrounding the central valley of California, while increases in boundary layer heights are observed over other regions in California. The number and duration of heat wave events are projected to increase substantially over the most populated parts of the State. The occurrence of marine air penetration events over the northern California is also projected to increase in the future. Keywords Dynamical downscaling • Climate change • Heat wave • Marine air penetration • California This paper has been reviewed by the staff of the California Air Resources Board and has been approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the California Air Resources Board, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

Effects of Anthropogenic and Biogenic Volatile Organic Compounds on Los Angeles Air Quality

“…In contrast to the considerable enhancement of BVOC emissions in Cases II, III, and IV, the relative change of BVOC emissions in Case V is only 4.6%, suggesting that climate change-induced meteorological variability in 2050 RCP8.5 scenario will have less of an impact on BVOC emissions in LA county than the increased tree cover fraction due to urban greening. This phenomenon is mainly attributed to the moderate temperature increase (approximately 1.0 °C) over LA county predicted by the climate model, which is consistent with findings reported in previous studies. , …”

“…Case V is adopted for exploring the impacts of future climate change on BVOC emissions by using the current BVOC emission factors and 18% tree cover fraction in 2014 and meteorological parameters in 2050 under the RCP8.5 scenario. Hourly meteorological parameters in 2050 were obtained from downscaled global bias-corrected climate model output data for the year 2050 from the Community Earth System Model (CESM1) that participated in phase 5 of the Coupled Model Intercomparison Experiment (CMIP5) ( last accessed: 10th June, 2021), which has been widely used in previous studies for investigating impacts of future climate change on California’s meteorological conditions and air quality. , The dynamic downscaling procedure is detailed in Zhao et al…”

“…Hourly meteorological parameters in 2050 were obtained from downscaled global bias-corrected climate model output data for the year 2050 from the Community Earth System Model (CESM1) that participated in phase 5 of the Coupled Model Intercomparison Experiment (CMIP5) (https://rda.ucar.edu/datasets/ds316.1/ last accessed: 10th June, 2021), which has been widely used in previous studies for investigating impacts of future climate change on California's meteorological conditions and air quality. 49,50 The dynamic downscaling procedure is detailed in Zhao et al 49 3. RESULTS AND DISCUSSION 3.1.…”

Impacts of Soil NOx Emission on O3 Air Quality in Rural California

“…In croplands, where nitrogen-rich fertilizers are applied to soils and have regular irrigation, NO x emissions can be significantly enhanced in comparison to the urban regions . Additionally, California has been experiencing warmer temperatures and increasing droughts. , Some rural regions, such as the Imperial Valley, San Joaquin Valley, and South Coast, also suffer from O 3 pollution that regularly exceeds government standards. , We thus choose California as a case study region and predict that SNO x could contribute to both NO x and O 3 distributions in the atmosphere. Our results provide insights needed for developing more effective emission reduction strategies to improve the air quality of California and other regions, especially in rural areas with a high prevalence of respiratory illnesses.…”

“…29 Additionally, California has been experiencing warmer temperatures and increasing droughts. 30,31 Some rural regions, such as the Imperial Valley, San Joaquin Valley, and South Coast, also suffer from O 3 pollution that regularly exceeds government standards. 2,15 We thus choose California as a case study region and predict that SNO x could contribute to both NO x and O 3 distributions in the atmosphere.…”