Outdoor Residential Water Use Restrictions during Recent Drought Suppressed Disease Vector Abundance in Southern California.

The California state government put restrictions on outdoor residential water use, including landscape irrigation, during the 2012-2016 drought. The public health implications of these actions are largely unknown, particularly with respect to mosquito-borne disease transmission. While residential irrigation facilitates persistence of mosquitoes by increasing the availability of standing water, few studies have investigated its effects on vector abundance. In two study sub-regions in the Los Angeles Basin, we examined the effect of outdoor residential water use restrictions on the abundance of the most important regional West Nile virus vector, Culex quinquefasciatus. Using spatiotemporal random forest models fit to Cx. abundance during drought and non-drought years, we generated counterfactual estimates of Cx. abundance under a hypothetical drought scenario without water use restrictions. We estimate that Cx. abundance would have been 44% and 39% larger in West Los Angeles and Orange counties, respectively, if outdoor water usage had remained unchanged. Our results suggest that drought, without mandatory water use restrictions, may counterintuitively increase the availability of larval habitats for vectors in naturally dry, highly irrigated settings and such mandatory water use restrictions may constrain Cx. abundance, which could reduce the risk of mosquito-borne disease while helping urban utilities maintain adequate water supplies.

Characterizing the Role of Wind and Dust in Traffic Accidents in California.

Wind is a common ground transportation hazard. In arid regions, wind-blown dust is an added risk. Here, we analyzed the relationship between accidents and wind speed, dust events to study how they may have contributed to vehicular accidents in California. The California Highway Patrol reports information about weather conditions that potentially contributed to traffic accidents, including a code for wind but not for reduced visibility due to dust. For the three counties that contain the major dust source regions in California (the Mojave Desert and the Imperial Valley), we found greater daily maximum wind speed for days with accidents coded for wind compared to all days with accidents. The percentage of people injured in accidents attributed for weather other than wind and coded for wind were the same; however, the percentage of people who died in wind-related accidents was about double the deaths in accidents caused by weather other than wind. At ground meteorological stations closest to accidents, we found lower median minimum visibility for days with wind-related accidents compared to all days with accidents. Across the region, wind speed recorded at ground meteorological stations increased the probability of high satellite-derived dust optical depth values. Over the period of 2006 to 2016, the correlation between daily minimum visibility and daily maximum satellite-estimated dust optical depth was negative. Our analysis of the correlation between dust and accidents shows that with increased wind storm and dust-event frequency in the future, the risk of traffic incidents due to wind and dust could increase.