Trends in precipitation days in the United States

Changes in precipitation frequency can have a major impact on many different sectors including agriculture, tourism, and recreation. This study investigates trends in precipitation days at first-order weather stations across the conterminous United States from 1951 to 2015. The Mann-Kendall test and sliding window correlation analysis are used to examine trends over time. Future precipitation days are forecasted via usage of a stepwise auto-regressive model. The Mann-Kendall test found that the majority of the Northeast and Midwestern states show upward trends in precipitation days, while negative trends are located in the Southeast and in clusters throughout the Northwest. Sliding window correlation analysis was used to detect the decade when most of the change in precipitation days occurred. The northeastern United States had more significant changes during the earlier decades whereas the centre part of the country had more significant changes in the later decades. Most stations saw more decades with positive (increasing) trends in precipitation days. Precipitation days are expected to increase for most of the United States into the future.