thumbnail

Comparison of Two Precipitation Gage Networks in Cook County, Illinois

Scientific Investigations Report 2025-5102
Prepared in cooperation with U.S. Army Corps of Engineers
By:
https://doi.org/10.3133/sir20255102

Links

Abstract

The Cook County Precipitation Network is a set of 25 precipitation gages established within Cook County, Illinois, on approximately a 5- to 7-mile square grid and used by the U.S. Army Corps of Engineers to help account for diversions of water from Lake Michigan to the State of Illinois. The transition from the precipitation gage network operated by the Illinois State Water Survey to the precipitation gage network operated by the U.S. Geological Survey (USGS) was compared for periods of overlapping data. This transition took place from May through September during the 2019 water year. The USGS was able to establish replacement precipitation gages at 17 of the 25 sites by the conclusion of the overlapping operational period.

The double-mass curve method was used to compare the two networks by creating a graph of the cumulated data collected by the Illinois State Water Survey and the comparable data collected by the USGS. Breaks in the double-mass curve method are caused by a change in the relation between variables. The eight sites that were installed following the overlapping period have a gap in the recorded data; however, the slope of the line for each of the eight sites is nearly equivalent to the previous data. In general, the cumulated precipitation data from the two networks were similar. Three sites had greater than 8-percent difference in their cumulative data ratios, located at Cicero, Ping Tom Park at Chicago, and South Shore, Ill.

Plain Language Summary

The Cook County Precipitation Network includes 25 precipitation gages spread out across Cook County, Illinois. These gages help the U.S. Army Corps of Engineers track how much water is diverted from Lake Michigan into Illinois. In 2019, the responsibility for operating and maintaining these gages shifted from the Illinois State Water Survey to the U.S. Geological Survey. To evaluate the data consistency during the transition, the two organizations operated their networks at the same time for a few months (May to September 2019). During this period, the U.S. Geological Survey installed new gages at 17 of the 25 sites. The remaining 8 sites were installed later, resulting in data gaps for those sites. An analytical method called a double-mass curve was used to compare the data from both networks. Overall, the precipitation totals from both networks were very similar. However, three sites had cumulative data ratio differences greater than 8 percent.

Suggested Citation

Johnson, K.K., 2026, Comparison of two precipitation gage networks in Cook County, Illinois: U.S. Geological Survey Scientific Investigations Report 2025–5102, 73 p., https://doi.org/10.3133/sir20255102.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Plain Language Summary
  • Abstract
  • Introduction
  • Comparison of Networks
  • Network Equipment
  • Summary
  • References Cited
  • Appendix 1. U.S. Army Corps of Engineers Supplied Monthly Data
  • Appendix 2. Station Descriptions of the U.S. Geological Survey Cook County Precipitation Network
Publication type Report
Publication Subtype USGS Numbered Series
Title Comparison of two precipitation gage networks in Cook County, Illinois
Series title Scientific Investigations Report
Series number 2025-5102
DOI 10.3133/sir20255102
Publication Date January 20, 2026
Year Published 2026
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Central Midwest Water Science Center
Description Report: iv, 73 p.; Linked Appendix Table; Dataset
Country United States
State Illinois
County Cook county
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Additional publication details