Comparing and Contrasting Daily Precipitation Extremes in the U.S. As Observed By Two Independent Observational Networks: The U.S. Cooperative Observer Program and the Long-Term Agroecosystem Research (LTAR) Network

In the United States, the COOP network is the most widely used precipitation network for climate detection and attribution studies. During the more than century long timespan when precipitation observations have been taken, changes in instruments and location, inadequate maintenance, dissimilar observation time, and the fact that measurements are made by a group of dedicated volunteers, have introduced uncertainty in the quality of the dataset. Alternately, the Long-Term Agroecosystem Research (LTAR) network, largely comprised of USDA-Agricultural Research Service Experimental Watersheds, and Ranges has been consistently and professionally measuring precipitation since the early 1930s. The purpose of this study is to compare changes in extreme daily precipitation characteristics during the warm season using paired rain gauges from the LTAR and COOP networks. The comparison, done at twelve LTAR sites located across the U.S., shows underestimation and overestimation of daily precipitation totals at the COOP sites compared to the reference LTAR observations. However, the magnitude and direction of the differences are not linked to the underlying precipitation climatology of the sites. Precipitation indices that focus on extreme precipitation characteristics match closely between the two networks at most of the sites. Our results show consistency between the COOP and LTAR networks when precipitation extremes are evaluated and constitute an extra layer of quality control for the COOP network. It also indicates that despite the discrepancies at the daily time steps, the extreme precipitation observed by COOP rain gauges can be reliably used to characterize changes in the hydrologic cycle due to natural and human causes.