A009-0011
Historic changes to convective environments and their impact on extreme precipitation in the northern North American Great Plains
Monday, 7 December 2020
Poster
Gabriel T Bromley, Montana State University, Department of Land Resources and Environmental Science, Bozeman, MT, United States, Andreas F Prein, National Center for Atmospheric Research, Boulder, CO, United States, Tobias Gerken, Pennsylvania State University, Department of Meteorology, University Park, PA, United States and Paul C. Stoy, Montana State University, Bozeman, MT, United States; University of Wisconsin Madison, Department of Biological Systems Engineering / Department of Atmospheric and Oceanic Sciences, Madison, WI, United States
Abstract:
The northern North American Great Plains (NNAGP) are a globally-important agricultural region and have undergone large shifts in agricultural practices – on the order of tens of millions of hectares – transitioning from traditional crop-fallow rotations to alternate cropping sequences. Since the 1970’s mean surface temperatures have decreased by 0.2 °C decade
-1 and surface vapor pressure deficit has decreased by 0.4 hPa decade
-1. This cooling and moistening was associated with a stark decrease in vegetation growing season Bowen ratio (from 2 to 1), increased convective likelihood (40% during May June) and increasing precipitation of 8 mm decade
-1 in during May and June in the eastern half of the NGP. Despite these changes it is still unclear how convective environments and extreme precipitation have responded to simultaneous climate and land use changes.
We use atmospheric sounding profiles acquired from the Integrated Global Radiosonde Archive to understand how convective parameters, such as CAPE, CIN and precipitable water have changed since the 1970s. Changes to precipitation are assessed using hourly gauge and Stage-IV radar data and over the United States and the MSWEP v2 3-hourly precipitation data over the United States and Canada. For Glasgow, MT the distribution of monthly maximum CAPE values has shifted such that the probability of exceeding 2000 J kg-1 has nearly tripled from 10% to 27%. Similarly, the distribution of CIN has shifted such that probability of CIN values exceeding -200 J kg-1 has increased from 34% to 41%. These changes highlight the rapid changing conditions in the NNAGP due to the complex interplay between local changes in land surface conditions and anthropogenic climate change.
