Warming enabled upslope advance in western US forest fires.

Increases in burned area and large fire occurrence are widely documented over the western United States over the past half century. Here, we focus on the elevational distribution of forest fires in mountainous ecoregions of the western United States and show the largest increase rates in burned area above 2,500 m during 1984 to 2017. Furthermore, we show that high-elevation fires advanced upslope with a median cumulative change of 252 m (-107 to 656 m; 95% CI) in 34 y across studied ecoregions. We also document a strong interannual relationship between high-elevation fires and warm season vapor pressure deficit (VPD). The upslope advance of fires is consistent with observed warming reflected by a median upslope drift of VPD isolines of 295 m (59 to 704 m; 95% CI) during 1984 to 2017. These findings allow us to estimate that recent climate trends reduced the high-elevation flammability barrier and enabled fires in an additional 11% of western forests. Limited influences of fire management practices and longer fire-return intervals in these montane mesic systems suggest these changes are largely a byproduct of climate warming. Further weakening in the high-elevation flammability barrier with continued warming has the potential to transform montane fire regimes with numerous implications for ecosystems and watersheds.

Electromagnetic waves' effect on airflow during air sparging.

Air sparging is a popular, yet slow, remediation technology for soil and groundwater contaminated with volatile organic compounds (VOCs). This paper theoretically and experimentally studies the effect of electromagnetic (EM) waves on air-channel formation within a glass-bead medium-used as an analogy to soil-during air-sparging experiments. The impact of EM waves on cleanup is not the focus of this paper, and the impact on airflow may or may not positively impact resulting cleanup process using air sparging to remove VOCs through volatilization. The hypothesis is that dielectrophoretic forces by EM waves can be used to alter airflow. Air injection was performed at different pressures, in the presence of EM waves (referred to as EM-stimulated) of various power and frequencies and the absence of EM waves (referred to as unstimulated). Digital images of the airflow patterns were collected, processed, and analyzed for all tests. The shape of the zone of influence (ZOI) was observed, and the radius of the zone of influence (ROI) was measured, which showed a 16% increase in ROI due to EM stimulation. An experimentally validated numerical simulation of the electric-field component of EM waves was developed. The correlation between EM-wave and air sparging characteristics were then studied using the numerical simulation and acquired digital images of the airflow to investigate and validate that the dielectrophoretic mechanism is behind the EM effect on airflow.