skip to main content
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Diagnosing conditional anthropogenic contributions to heavy Colorado rainfall in September 2013

Abstract

The Colorado floods of September 2013 caused severe damage and fatalities, and resulted from prolonged heavy rainfall unusual for that time of year – both in its record-breaking amounts and associated weather systems. We investigate the possible role of anthropogenic climate change in this extreme event. The unusual hydrometeorology of the event, however, challenges standard frameworks for attributing extreme events to anthropogenic climate change, because they typically struggle to simulate and connect the large-scale meteorology associated with local weather processes. Therefore we instead employ a part dynamical modelling- part observational- based event attribution approach, which simulates regional Colorado rainfall conditional on boundary conditions prescribed from the observed synoptic-scale meteorology in September 2013 – and assumes these conditions would have been similar in the absence of anthropogenic forcing. Using this ‘conditional event attribution’ approach we find that our regional climate model simulations indicate that anthropogenic drivers increased the magnitude of heavy northeast Colorado rainfall for the wet week in September 2013 by 30%, with the occurrence probability of a week at least that wet increasing by at least a factor of 1.3. By comparing the convective and large-scale components of rainfall, we find that this increase resulted in part from themore » additional moisture-carrying capacity of a warmer atmosphere – allowing more intense local convective rainfall that induced a dynamical positive feedback in the existing larger scale moisture flow – and also in part from additional moisture transport associated with larger scale circulation change. Our approach precludes assessment of changes in the frequency of the observed synoptic meteorological conditions themselves, and thus does not assess the effect of anthropogenic climate drivers on the statistics of heavy Colorado rainfall events. However, tailoring analysis tools to diagnose particular aspects of localized extreme weather events, conditional on the observed large-scale meteorology, can prove useful for diagnosing the physical effects of anthropogenic climate change on severe weather events – especially given large uncertainties in assessments of anthropogenic driven changes in atmospheric circulation.« less

Authors:
 [1];  [2];  [1];  [1];  [3];  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Texas A & M Univ., College Station, TX (United States)
  3. Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1525236
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Weather and Climate Extremes
Additional Journal Information:
Journal Volume: 17; Journal Issue: C; Journal ID: ISSN 2212-0947
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Pall, Pardeep, Patricola, Christina M., Wehner, Michael F., Stone, Dáithí A., Paciorek, Christopher J., and Collins, William D. Diagnosing conditional anthropogenic contributions to heavy Colorado rainfall in September 2013. United States: N. p., 2017. Web. doi:10.1016/j.wace.2017.03.004.
Pall, Pardeep, Patricola, Christina M., Wehner, Michael F., Stone, Dáithí A., Paciorek, Christopher J., & Collins, William D. Diagnosing conditional anthropogenic contributions to heavy Colorado rainfall in September 2013. United States. doi:10.1016/j.wace.2017.03.004.
Pall, Pardeep, Patricola, Christina M., Wehner, Michael F., Stone, Dáithí A., Paciorek, Christopher J., and Collins, William D. Tue . "Diagnosing conditional anthropogenic contributions to heavy Colorado rainfall in September 2013". United States. doi:10.1016/j.wace.2017.03.004. https://www.osti.gov/servlets/purl/1525236.
@article{osti_1525236,
title = {Diagnosing conditional anthropogenic contributions to heavy Colorado rainfall in September 2013},
author = {Pall, Pardeep and Patricola, Christina M. and Wehner, Michael F. and Stone, Dáithí A. and Paciorek, Christopher J. and Collins, William D.},
abstractNote = {The Colorado floods of September 2013 caused severe damage and fatalities, and resulted from prolonged heavy rainfall unusual for that time of year – both in its record-breaking amounts and associated weather systems. We investigate the possible role of anthropogenic climate change in this extreme event. The unusual hydrometeorology of the event, however, challenges standard frameworks for attributing extreme events to anthropogenic climate change, because they typically struggle to simulate and connect the large-scale meteorology associated with local weather processes. Therefore we instead employ a part dynamical modelling- part observational- based event attribution approach, which simulates regional Colorado rainfall conditional on boundary conditions prescribed from the observed synoptic-scale meteorology in September 2013 – and assumes these conditions would have been similar in the absence of anthropogenic forcing. Using this ‘conditional event attribution’ approach we find that our regional climate model simulations indicate that anthropogenic drivers increased the magnitude of heavy northeast Colorado rainfall for the wet week in September 2013 by 30%, with the occurrence probability of a week at least that wet increasing by at least a factor of 1.3. By comparing the convective and large-scale components of rainfall, we find that this increase resulted in part from the additional moisture-carrying capacity of a warmer atmosphere – allowing more intense local convective rainfall that induced a dynamical positive feedback in the existing larger scale moisture flow – and also in part from additional moisture transport associated with larger scale circulation change. Our approach precludes assessment of changes in the frequency of the observed synoptic meteorological conditions themselves, and thus does not assess the effect of anthropogenic climate drivers on the statistics of heavy Colorado rainfall events. However, tailoring analysis tools to diagnose particular aspects of localized extreme weather events, conditional on the observed large-scale meteorology, can prove useful for diagnosing the physical effects of anthropogenic climate change on severe weather events – especially given large uncertainties in assessments of anthropogenic driven changes in atmospheric circulation.},
doi = {10.1016/j.wace.2017.03.004},
journal = {Weather and Climate Extremes},
number = C,
volume = 17,
place = {United States},
year = {2017},
month = {7}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 13 works
Citation information provided by
Web of Science

Figures / Tables:

Fig. 1 Fig. 1: Modelled synoptic situation and change for the rainy week of September 2013. (a) Total 7-day (00Z 9 September – 00Z 16 September 2013) precipitable water (g/Kg), and average 7-day 700 hPa winds (m/s) over the WRF model domain. Values are ensemble-averages over an ensemble of 101 WRF modelmore » simulations under anthropogenic conditions. (b) Corresponding change (%) relative to the ensemble-average of 101 WRF model simulations under non-anthropogenic conditions. Black box demarcates the northeast Colorado target area, including Boulder.« less

Save / Share:
Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.