The changing nature of flooding across the central …...The Changing Nature of Flooding across the Central United States SUPPLEMENTARY FIGURE 3. Fractional contribution of the different

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NCLIMATE2516

NATURE CLIMATE CHANGE | www.nature.com/natureclimatechange 1

The Changing Nature of Flooding across the Central United States

SUPPLEMENTARY FIGURE 1. These maps summarize the results for trends in the magnitude (panels A and C) and frequency (panels B and D) of flood events for 68 stations in Hirsch and Ryberg (2011). These stations are “from basins with little or no reservoir storage or urban development (less than 150 persons per square kilometre in 2000).” The blue (red) triangles indicate the location of the stations with increasing (decreasing) trends at the 5% level. The results in panels A and B are based on the entire available record length at each station, while the results in panels C and D are based on the common 1962-2011 time period. In panel A, there are 18 (4) stations with statistically significant increasing (decreasing) trends in magnitude. In panel B, there are 33 (1) stations with statistically significant increasing (decreasing) trends in frequency. In panel C, there are 8 (1) stations with statistically significant increasing (decreasing) trends in magnitude. In panel D, there are 22 (3) stations with statistically significant increasing (decreasing) trends in frequency. The grey circles refer to the location of the stations that did not experience statistically significant changes (at the 5% level).

The changing nature of flooding across thecentral United States

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SUPPLEMENTARY INFORMATION DOI: 10.1038/NCLIMATE2516







SUPPLEMENTARY FIGURE 2. These maps summarize the results for trends in the magnitude (A-D) and frequency (E-H) of flood events. The blue (red) triangles indicate the location of the stations with increasing (decreasing) trends at the 5% level. The grey circles refer to the location of the stations that did not experience statistically significant changes (at the 5% level). Analyses are performed over the entire record length that is available at each location.






SUPPLEMENTARY FIGURE 3. Fractional contribution of the different seasons to the seasonality of annual maximum daily discharge records (A-D) and peaks-over-threshold flood events (E-H).






SUPPLEMENTARY FIGURE 4. Fractional contribution of the different seasons to the seasonality of annual maximum daily rainfall records (A-D) and peaks-over-threshold daily events (E-H).Precipitation analyses are based on the unified Gauge-Based daily observation data (Higgins et






al. 2000) that are available from the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC). This daily product has a grid resolution of 0.25-degree.






SUPPLEMENTARY FIGURE 5. Maps showing the presence of trends in seasonal temperature over the 1948-2011 time period. Results are significant at the 5% level. Analyses are based on the gridded monthly mean surface air temperatures by the University of Delaware (Willmott andRobeson 1995). This product has a grid resolution of 0.5-degree.






SUPPLEMENTARY FIGURE 6. Trends in annual precipitation over the 1948-2012 time period.Precipitation analyses are based on the unified Gauge-Based daily observation data (Higgins et al. 2000) that are available from the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC). This daily product has a grid resolution of 0.25-degree.






SUPPLEMENTARY FIGURE 7. Trends in seasonal precipitation over the 1948-2012 time period.Precipitation analyses are based on the unified Gauge-Based daily observation data (Higgins et al. 2000) that are available from the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC). This daily product has a grid resolution of 0.25-degree.






SUPPLEMENTARY FIGURE 8. Map showing the location of the 774 U.S. Geological Survey (USGS) stations used in this study. The grey boundaries represent the USGS Hydrologic Unit Code (HUC) 8.






SUPPLEMENTARY FIGURE 9. Number of available stream flow gauges over the study period (left panel) and histogram with the record length for the 774 stations (right panel). The stations have at least 50 years of daily data, ending no earlier than 2011. The majority of the stations have between 60 and 80 years of data.






SUPPLEMENTARY FIGURE 10: These maps summarize the results for trends in the magnitude

(panels A and C) and frequency (panels B and D) of flood events. The blue (red) triangles

indicate the location of the stations with increasing (decreasing) trends at the 5% level. The grey

circles refer to the location of the stations that did not experience statistically significant changes

(at the 5% level). Panels A and B (C and D) show the results for the trend analysis accounting (or

not) for the presence of abrupt changes. These results refer to the entire record length for each

station. Consult Supplementary Figure 11 for the record length used in panels A and B.






SUPPLEMENTARY FIGURE 11: These maps show the record length used for the analyses in

Supplementary Figure 10 (A-B). Panels A and C refer to trends in the magnitude, while B and D

refer to trends in frequency. Panels A and B show the record length for the stations with

statistically significant trends in panels A and B. The results in panels C and D show the record

length regardless of the statistical significance.






References

Higgins, R.W., Shi, W., Yarosh, E., & Joyce, R. Improved United States precipitation quality control system and analysis, NCEP/Climate Prediction Center Atlas 7, 40 pp. (2000).

Hirsch, R.M. & Ryberg, K.R. Has the magnitude of floods across the USA changed with global CO2 levels? Hydrolog. Sci. J., 57(1), 1-9 (2012).

Willmott, C.J. & Robeson, S.M. Climatologically aided interpolation (CAI) of terrestrial air temperature. Int. J. Climatol. 15, 221-229 (1995).



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The changing nature of flooding across the central …...The Changing Nature of Flooding across the Central United States SUPPLEMENTARY FIGURE 3. Fractional contribution of the different