Downscaling a global climate model to simulate climate change over the US and the implication on regional and urban air quality

Abstract

Climate change can exacerbate future regional air pollution events by making conditions more favorable to form high levels of ozone. In this study, we use spectral nudging with the Weather Research and Forecasting (WRF) model to downscale NASA earth system GISS modelE2 results during the years 2006 to 2010 and 2048 to 2052 over the contiguous United States in order to compare the resulting meteorological fields from the air quality perspective during the four seasons of five-year historic and future climatological periods. GISS results are used as initial and boundary conditions by the WRF regional climate model (RCM) to produce hourly meteorological fields. The downscaling technique and choice of physics parameterizations used are evaluated by comparing them with in situ observations. This study investigates changes of similar regional climate conditions down to a 12 km by 12 km resolution, as well as the effect of evolving climate conditions on the air quality at major US cities. The high-resolution simulations produce somewhat different results than the coarse-resolution simulations in some regions. Also, through the analysis of the meteorological variables that most strongly influence air quality, we find consistent changes in regional climate that would enhance ozone levels in four regions of the US during fall (western US, Texas, northeastern, and southeastern US), one region during summer (Texas), and one region where changes potentially would lead to better air quality during spring (Northeast). Changes in regional climate that would enhance ozone levels are increased temperatures and stagnation along with decreased precipitation and ventilation. We also find that daily peak temperatures tend to increase in most major cities in the US, which would increase the risk of health problems associated with heat stress. Future work will address a more comprehensive assessment of emissions and chemistry involved in the formation and removal of air pollutants

The regional MiKlip decadal forecast ensemble for Europe: the added value of downscaling

“…The long-term means and trends of our regional simulations belong (by definition) not to the quantities, which vary on decadal time scales; hence, they are not the subject of our assessment of decadal predictability. The long-term performance of the initialised predictions is, in principle, similar to the long-term performance of the projections (Feldmann et al, 2013;Wagner et al, 2013;Berg et al, 2013;Trail et al, 2013). Figure 4 shows the correlation coefficient and the reliability for Europe of summer precipitation sums for lead years 1-5.…”

“…For climate projections and climate assessment, this has been shown to yield added value (Feldmann et al, 2013;Wagner et al, 2013;Berg et al, 2013;Trail et al, 2013). Whether such added value can also be found in regionally downscaled predictions is presently an open question and one of the aims of this study.…”

Air Quality and Climate Connections

“…First, variations in weather on weekly to annual scales introduce an uncontrollable random component that can mask the true efficacy of air quality improvement strategies in the short-term (Gégo et al, 2007). Second, climate change can alter regional meteorology conducive to pollutant buildup, imposing a "climate penalty" (see Key Terms) or, for example, can enhance ventilation of the polluted boundary layer, yielding a "climate benefit" (e.g., Trail et al, 2013). A quantitative understanding of how air pollution meteorology responds to climate change and natural variability is needed to inform air quality planning and regulation accountability for the coming decades (Ravishankara et al, 2012;Dawson et al, 2013).…”

Projected changes in haze pollution potential in China: an ensemble of regional climate model simulations

“…Longer WVDs indicate more haze pollution incidents. The threshold of 6000 m 2 s −1 for the ventilation coefficient was widely used, not only in the USA (Hanson and McKee, 1983;Leung and Gustafson, 2005;Trail et al, 2013) but also in other places such as India (Goyal and Rao, 2007;Manju et al, 2002), Athens (Kassomenos et al, 1995) and Thailand (Pimonsree, 2008). A sensitivity analysis shows that there is little change in the relationship between WVDs and the haze days if using different thresholds to calculate WVDs.…”

“…To validate the performance of the RegCM4 downscaling simulations, the ERA-Interim reanalysis data set (Uppala et al, 2008) with the horizontal resolution of 0.75 • × 0.75 • was employed as observations, including 6 h boundary layer height, precipitation, geopotential height, and wind speed.…”