Sensitivity of Airborne Dust to Drought in the U.S. Southwest: What Are the Implications for Public Health under Future Climate Change?

The southwest U.S. (Arizona, Colorado, New Mexico, and Utah) is projected to experience severe droughts in the coming decades due to climate change. While previous studies have linked past fluctuations in dust activity to hydroclimate variability and human land disturbance, the extent to which future increases in aridity could impact airborne dust levels and public health remains poorly quantified. Here, we investigate the sensitivity of fine dust (soil-derived PM_2.5) and coarse mass (PM_2.5-10) levels in the Southwest to regional drought conditions, using the Standardized Precipitation-Evapotranspiration Index (SPEI) as a drought proxy. The observed relationships are then used to estimate changes in dust levels and associated health impacts under future scenarios consistent with the U.S. Environmental Protection Agency's Climate Change Impacts and Risk Analysis (CIRA) framework. Empirical Orthogonal Function analysis of ground-based measurements reveal that in each season, the most dominant modes of year-to-year changes in fine dust and in coarse mass anomalies display patterns of coherent variability across the Southwest, which is indicative of large-scale influence by controlling factors. These modes are strongly correlated to the SPEI accumulated over 1–6 months in local and surrounding regions, which are representative of soil moisture conditions. Historically, a unit decrease in the 2-month SPEI averaged over southwestern North America is associated with seasonal mean increases of 0.22–0.44 𝜇g m⁻³ fine dust and of 1.10–2.19 𝜇g m⁻³ coarse mass averaged across the US Southwest (p < 0.05). We then apply these observed sensitivities to estimate changes in fine dust and coarse mass through 2099 under two Representative Concentration Pathways (RCP4.5 and RCP8.5), using bias-corrected downscaled meteorological outputs from six CMIP5 models. We estimate the excess premature mortality and morbidity attributable to the projected changes in dust concentrations by combining our projections with epidemiological relationships describing health risks due to PM_2.5 and coarse mass exposures, and projections of future population baseline incidence rates. Our findings highlight the potential for climate change to increase public health risks due to exacerbating droughts and air pollution in many populated arid regions around the world.