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.
Highlights
California has substantially improved its air quality over the past decades with effective emission control strategies, it still remains as one of the most polluted states in the United States
Many high particulate matter (PM) episodes in California’s San Joaquin Valley (SJV) are largely due to stagnation associated with meteorological drivers such as low planetary boundary layer height (PBLH) and low wind speed, which are sometimes induced by the intrusion of Pacific Subtropical High (PSH) located west of California to SJV (Zhao et al 2011a)
We have investigated the climate change impact on meteorological variables and extreme events for different geographical sub-regions in California by dynamically downscaling Community Earth System Model (CESM) data from Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations with the RCP6.0 emission scenario using the WRF model
Summary
California has substantially improved its air quality over the past decades with effective emission control strategies, it still remains as one of the most polluted states in the United States During summertime, when ozone is the primary pollutant of concern, air temperature and ventilation are crucial factors affecting ozone production and buildup (Sillman 2000) Both the frequency and magnitude of heat waves have been shown to increase in California during summer, which are at least partially induced by climate change (Gershunov et al 2009; Meehl and Tebaldi 2004). The primary goal of this study is to explore the future projection of air pollution-relevant meteorological variables (e.g., temperature, wind, precipitation and ventilation) and important atmospheric phenomena (e.g., heat wave events, MAP events and droughts) over California in greater detail using the aforementioned dynamical downscaling with bias correction (i.e., the mean bias correction plus the adjustment of inter-annual variations). In addition to evaluating the dynamical downscaling method with bias correction applied to the CESM data, this paper presents the climate change impact on summertime meteorological conditions and atmospheric phenomena.
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