A Historical Perspective on U.S. Weather and Climate Extremes
WHAT HISTORY TELLS US ABOUT U.S. DAILY RAINFALL EXTREMES - METHODSBased on Hoerling et al. & Wolter et al. (2016), we utilize 987 meteorological stations in the contiguous US extracted from GHCN-D (Menne et al. 2012) with at least 100 years of non-missing daily observations during 1901–2014, as well as mostly complete data in 2015. The “RX1day” index (maximum 1-day precipitation), as defined by Sillmann et al. (2013), is computed at each station for all annual and bimonthly cases (base period 1901–80). We applied the generalized extreme value (GEV) distribution, known as the block or annual maxima approach for analysis of 20-yr precipitation events, using the Matlab NEVA package (Cheng et al. 2014). The lower confidence bounds (2.5th percentile) of the GEV-estimated return level for 20-yr events are applied in order to include all cases that might be considered of that intensity. We validated these results against the empirical estimates of the 20-yr events by ranking the annual and seasonal maxima at each station.
Figure 1: Bimonthly daily extremes in excess of the lower estimate for 20-yr events for March-April 2017
DiscussionMarch-April 2017 had the 3rd highest count of 20-yr daily precipitation events since 1901 (16.4% of all available stations). This count was anchored by the regional totals in the Ohio Valley (25.4%) and South (27.2%). Two extreme March-April seasons in a row in the South (2016 with highest count on record, and 2017 with 3rd highest) anchor a statistically significant linear upward trend in this region.
Figure 1: Bimonthly daily extremes in excess of the lower estimate for 20-yr events for September-October 2016
DiscussionSeptember-October 2016 had the 4th highest national count of 20-yr daily precipitation events since 1901 (18.3% of all available stations). This count was boosted by regional totals in the Northwest (45.1%, highest on record)) and West (36.6%. 4th highest). Both of these regions show little trend over the last 116 years in all seasons of the calendar year, not just in September-October. Hurricane Matthew skirted the southeastern seaboard around the 10th of October, leading to flooding rains that caused 49 fatalities and around $10B in damages (Southeast coverage: 22.3%, 12th highest since 1901). Source: https://www.ncdc.noaa.gov/billions/events
Figure 1: Bimonthly daily extremes in excess of the lower estimate for 20-yr events for July-August 2016
DiscussionJuly-August 2016 had the 6th highest count of 20-yr events since 1901 (13.1% of all available stations), highest in the Midwest climate region (Fig. 2) where 27.4% of the stations were flagged in this manner, 2nd only to 2007. The Ohio valley tallied 19.3% of its stations with such daily extremes, 3rd highest on record. These two regions are the only two to show significant upward trends in this season (5.3% and 3.5% per century, respectively). In the South climate region (Fig. 2), flooding rains around August 12-15 caused 13 deaths in Louisiana along with estimated damages around $10B. Source: https://www.ncdc.noaa.gov/billions/events
Figure 1: Bimonthly daily extremes in excess of the lower estimate for 20-yr events for March-April 2016
DiscussionMarch-April 2016 tallied the highest national count on record for this season’s 20-yr events since 1901 (20.0% of all available stations). This was anchored by record totals in the Northern Rockies (33.6%; mainly in Nebraska) and South (41.3%). These two regions show significant upward trends in this season (just over 4% per century each), although the upward trend in the South did not even reach the 90% significance threshold before 2015. In contrast, the Southwest has the only significant downward trend during this season (-4.9% per century) in the country. Texas and Louisiana suffered through multiple flooding events, most notably in the Sabine River basin on March 12th (5 fatalities; $2.3B) and around Houston on April 17-18 ($2.7; 8 fatalities). Source: https://www.ncdc.noaa.gov/billions/events
Figure 1: Bimonthly daily extremes in excess of the lower estimate for 20-yr events for November-December 2015
DiscussionNovember-December 2015 saw more 20-yr events in this season than in any other year on record (29.0%). These extreme daily totals were mostly associated with a powerful storm system that swept northeastward from Texas through the Upper Midwest in late December, causing at least 50 deaths and $2B in damages. Regional record counts for the season were set in the Midwest (50.4%), Ohio Valley (39.9%), and South (36.6%). It is noteworthy that these regional records were NOT preceded by significant upward trends over the last century. Source: https://www.ncdc.noaa.gov/billions/events
U.S. Climate Regions
Click on a region to display data for that region, or here for Continental U.S.
Continental U.S. 20yr Precipitation ExtremesExtreme Weather and Climate datasets are compiled for the US Climate Regions and the continental US. Raw data can be accessed here.
Totals by time period:
Annual Totals by period
Values in the table are the percent of available stations that exceeded the 20yr Precipitation for each time period.
- Cheng, L., A. AghaKouchak, E. Gilleland, and R. W. Katz, 2014: Non-stationary extreme value analysis in a changing climate. Climatic Change, 127, 353–369. doi:10.1007/s10584-014-1254-5
- Hoerling, M., J. Eischeid, J. Perlwitz, X. Quan, and K. Wolter, 2016: Characterizing Recent Trends in U.S. Heavy Precipitation. J. Climate, 29, 2313-2332. doi:10.1175/JCLI-D-15-0441.1
- Menne, M. J., I. Durre, R. S. Vose, B. E. Gleason, and T. G. Houston, 2012: An overview of the Global Historical Climatology Network-Daily Database. J. Atmos. Oceanic Tech., 29, 897–910. doi:10.1175/JTECH-D-11-00103.1
- Sillmann, J., V. V. Kharin, X. Zhang, F. W. Zwiers, and D. Bronaugh, 2013: Climate extreme indices in the CMIP5 multimodel ensemble: Part 1. Model evaluation in the present climate. J. Geophys. Res. Atmos., 118, 1716–1733. doi:10.1002/jgrd.50203
- Wolter, K., M. Hoerling, J.K. Eischeid, and L. Cheng, 2016: What History Tells us about 2015 US Daily Rainfall Extremes (in "Explaining Extremes of 2015 from a Climate Perspective"). Bull. Amer. Meteor. Soc., 97, S9-S13. doi:10.1175/BAMS-D-16-0166.1 PDF
- Explaining extreme events in 2015 from a climate perspective - Press Conference
NOAA's Martin Hoerling explains the context for precipitation extremes