Tracking precipitation patterns across a western U.S. metropolitan area using volunteer observers: RainLog.Org

The southwestern United States experiences extreme hydroclimatic variability, including intense but localized monsoon thunderstorms, tropical storms, and winter storms, resulting in complex and variable patterns of precipitation over space and time. Official gauges associated with long-term monitoring networks are sparsely distributed throughout the region and are unable to capture the spatial complexity and variability of these precipitation patterns. The RainLog program, a volunteer precipitation monitoring program, was started in southern Arizona in 2005 to leverage enthusiasm among non-scientists around weather, water, and climate to address the gaps in official monitoring networks. An examination of the portion of the dataset that spans the Tucson metropolitan area illustrates the opportunities and challenges in using volunteer data to track precipitation. We compare near-complete records to an official observation to highlight how the broader RainLog network supports characterizing hydroclimatic variability over the period of record. We also examine several case study events drawn from metrics of network variability that represent different forms of hydroclimatic extremes. We find that in most cases the RainLog network captures a range of precipitation values that were notably different than the single value recorded at the official observing site, adding substantial value in recording and reconstructing past extreme precipitation events. This work highlights how volunteer citizen science precipitation monitoring networks can provide critical data for tracking precipitation variability and changes, although are only one complementary piece of coherent, long-term hydroclimatic monitoring.