Drought-sensitivity of fine dust in the US Southwest: Implications for air quality and public health under future climate change

Abstract

We investigate the present-day sensitivity of fine dust levels in the U.S. Southwest to regional drought conditions and use the observed relationships to assess future changes in fine dust levels and associated health impacts under climate change. Empirical Orthogonal Function analysis reveals that the most dominant mode of fine dust interannual variability for each season consists of a pattern of large-scale co-variability across the Southwest. This mode is strongly correlated to the Standardized Precipitation-Evapotranspiration Index (SPEI) accumulated over 1-6 months in local and surrounding regions spanning the major North American deserts. Across the seasons, a unit decrease in 2-month SPEI averaged over the U.S. Southwest and northern Mexico is significantly associated with increases in Southwest fine dust of 0.22-0.43 μg m-3. We apply these sensitivities to statistically downscaled meteorological output from 22 climate models following two Representative Concentration Pathways (RCPs), and project future increases in seasonal mean fine dust of 0.04-0.10 μg m-3 (5-8%) under RCP2.6 and 0.15-0.55 μg m-3 (26-46%) under RCP8.5 relative to the present-day (2076-2095 vs. 1996-2015). Combined with the same projections of future population and baseline incidence rates, annual premature mortality attributable to fine dust exposure could increase by 140 (24%) deaths under RCP2.6 and 750 (130%) deaths under RCP8.5 for adults aged ≥30 years, and annual hospitalizations due to cardiovascular and respiratory illnesses could increase by 170 (59%) admissions under RCP2.6 and 860 (300%) admissions under RCP8.5 for adults aged ≥65 years in the Southwest relative to the present-day. Our results highlight a climate penalty that has important socioeconomic and policy implications for the U.S. Southwest but is not yet widely recognized.