The changing bioclimate of Las Vegas, NV

Using hourly meteorological data from McCarran International Airport for the period 1961-2004, bioclimatic trends in the fastest growing city in the United States, Las Vegas, Nevada, are analyzed using linear regression analysis and difference of means testing. Over the last four decades, significant changes in human thermal comfort have occurred in Las Vegas due to a combination of higher temperatures from the urban heat island (UHI) effect and increasing dewpoint temperatures. Moreover, due to the increased heat storage of the urban fabric, temperatures are remaining higher throughout the late afternoon and evening hours, exacerbating the already extreme climate of the region. For instance, the number of hours annually with temperatures ≥ 38°C (100°F) increased by 43% (an additional 146 hours per year). Meanwhile, the average summer dewpoint increased by as much as 8°C leading to significantly higher heat index values and reduced outdoor comfort. Balanced against increased summer heat stress, the winter climate of Las Vegas has moderated substantially. Since 1961, the number of hours below freezing decreased from 230 hours to only 12 in 2004, a 95% decrease. Finally, spatial synoptic classification (SSC) data for Las Vegas is analyzed to demonstrate that increased moisture levels are likely the result of local land use changes, not changes in the synoptic climate of the region.