The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is a large and growing community of volunteers measuring and reporting precipitation and is making this information broadly available for the research and operational community. CoCoRaHS has evolved through several phases since its beginnings in 1998, first starting as a flood-motivated local Colorado Front Range project, then through a 5-yr nationwide expansion period (2005–09), followed by five years (2010–14) of internal growth and capacity building. As of mid-2015, CoCoRaHS volunteers have submitted over 31 million daily precipitation reports and tens of thousands of reports of hail, heavy rain, and snow, representing over 1.5 million volunteer hours. During the past 10 years, there has been wide demand for and use of CoCoRaHS data by professional and scientific users with an interest in its applicability to their different areas of focus. These range from hydrological applications and weather forecasting to agriculture, entomology, remote sensing validation, city snow removal contracting, and recreational activities, just to name a few. The high demand for CoCoRaHS data by many entities is an effective motivator for volunteer observers, who want to be assured that their efforts are needed and appreciated. Going forward, CoCoRaHS hopes to continue to play a leading role in the evolution and growth of citizen science while contributing to research and operational meteorology and hydrology.

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This article introduces two new tools developed to enhance drought impacts monitoring by citizen scientists. In collaboration with the National Integrated Drought Information System (NIDIS), the National Drought Mitigation Center (NDMC), and the Community Collaborative Rain, Hail and Snow (CoCoRaHS) network, the Carolinas Integrated Sciences and Assessments (CISA) developed an experimental method of drought monitoring and reporting by citizen scientists. Since 2013, CISA has recruited CoCoRaHS observers in the Carolinas to participate in “condition monitoring,” the regular reporting of local conditions. In contrast to intermittent drought impact reports, condition monitoring creates a baseline for comparison of change through time and improves understanding of the onset, intensification, and recovery of drought. A project evaluation demonstrated the usefulness of the qualitative reports, while also identifying a need for improved accessibility to the information and a quantitative metric to more quickly assess changing conditions. Evaluation findings informed the development of 1) a condition monitoring scale bar for inclusion on the national CoCoRaHS reporting form and 2) a web map to spatially display the condition monitoring reports. CoCoRaHS observers use the scale bar to record their assessment of local conditions, ranging from severely wet to severely dry. Their qualitative reports provide more in-depth information about their selection, noting the effects of weather and climate on the environment and communities in their area. The web map provides an easily accessible format for users such as the State Climate Offices to view the reports, facilitating the incorporation of CoCoRaHS observations into drought monitoring processes.

CoCoRaHS is a multinational citizen science project for observing precipitation. Like many citizen science projects, volunteer retention is a key measure of engagement and data quality. Through survival analysis, we found that participant age (self-reported at account creation) is a significant predictor of retention. Compared to all other age groups, participants aged 60-70 are much more likely to sign up for CoCoRaHS, and to remain active for several years. We also measured the influence of task difficulty and the relative frequency of rain, finding small but statistically significant and counterintuitive effects. Finally, we confirmed previous work showing that participation levels within the first month are highly predictive of eventual retention. We conclude with implications for observational citizen science projects and crowdsourcing research in general.