Evaluating the reliability of the U.S. Cooperative Observer Program precipitation observations for extreme events analysis using the LTAR network

Authors: Demaria, Eleonora; Goodrich, David - Dave; KUNKEL, K.E. - National Oceanic & Atmospheric Administration (NOAA)

Submitted to: Journal of Atmospheric and Ocean Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2018
Publication Date: 3/1/2019
Citation: Demaria, E.M., Goodrich, D.C., Kunkel, K. 2019. Evaluating the reliability of the U.S. Cooperative Observer Program precipitation observations for extreme events analysis using the LTAR network. Journal of Atmospheric and Ocean Technology. 36:317-332.

Interpretive Summary: The evaluation of climate change impacts on precipitation extremes in the US relies on a network of rain gauges that is operated by dedicated volunteers. The U.S. Cooperative Observer Program (COOP) network has more than 8,000 rain gauges which allows continental scale analysis, but it has reported inconsistencies in the measurement time, changes in rain gauge instruments and locations, and inadequate maintenance, among others. The study uses an independent precipitation dataset from the USDA-ARS operated Long-Term Agroecosystem Research (LTAR) network to validate the characteristics of extreme precipitation measured by the COOP network. We pair rain gauges from each network at 12 LTAR sites located across the US. Daily precipitation for the period 1970-2014 are used to evaluate differences in daily total and daily extreme precipitation indices among the networks. Our analysis shows that the magnitude and trend of extreme precipitation indices match closely between networks despite the differences in elevation and distance between paired rain gauges. This indicates that the COOP rain gauges can be reliably used to characterize changes in the hydrologic cycle due to natural and human causes.

Technical Abstract: The detection and attribution of changes in precipitation characteristics relies on dense networks of rain gauges. In the U.S., the COOP network is widely used for such studies even though there are reported inconsistencies due to changes in instruments and location, inadequate maintenance, dissimilar observation time, and the fact that measurements are made by a group of dedicated volunteers. Alternately, the recently created Long-Term Agroecosystem Research (LTAR) network 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.