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Changes in hail and flood risk in high-resolution simulations over Colorado's mountains


The effect of a warming climate on hailstorm frequency and intensity is largely unknown. Global climate models have too coarse resolution to simulate hailstorms explicitly; thus it is unclear if a warmer climate will change hailstorm frequency and intensity, and if so, whether such events will become more likely through intensified thunderstorms or less likely owing to overall warmer conditions. Here we investigate hail generation and maintenance for warm-season extreme precipitation events in Colorado, USA, for both present-day and projected future climates using high-resolution model simulations capable of resolving hailstorms. Most simulations indicate a near-elimination of hail at the surface in future simulations for this region, despite more intense future storms and significantly larger amounts of hail generated in-cloud. An increase in the height of the environmental melting level due to climate warming is found to be the primary reason for the disappearance of surface hail, as the warmer atmosphere increases the melting of frozen precipitation. A decrease in future surface hail at high-elevation locations may imply potential changes in both hail damage and flood risk.

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Figure 1: A comparison of precipitation and hail/graupel accumulation for PAST and FUT simulations.
Figure 2: A comparison of hail throughout the full atmospheric column.
Figure 3: A comparison of graupel/hail amount by vertical level in PAST and FUT simulations.
Figure 4
Figure 5: A comparison of precipitation, hail/graupel and surface runoff relative to elevation.


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This research was supported by the Postdocs Applying Climate Expertise (PACE) Fellowship Program, administered by the University Corporation for Atmospheric Research, jointly funded by the National Oceanic and Atmospheric Administration (NOAA), the Bureau of Reclamation, and the Western Water Assessment. We acknowledge NCAR and the National Science Foundation (NSF) for the availability of the WRF model and NCL software, and Unidata for the IDV package. We also wish to thank the NARCCAP project for providing the RCM data used in this paper. NARCCAP is funded by the NSF, the US Department of Energy (DoE), NOAA, and the US Environmental Protection Agency Office of Research and Development (EPA). Gratitude is extended to NOAA ESRL’s Jet Supercomputing system for providing computer resources for this work.

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K.M. carried out the model simulations and led the writing of the paper. M.A.A. provided project planning and leadership, as well as climate modelling expertise. G.T. contributed updated model microphysics code and provided microphysics parameterization counsel. J.J.B. provided project planning and counsel, and J.D.S. provided model initial condition files to be used for the high-resolution simulations, as well as reanalysis-based analyses, model validation, and graphics support. All contributed to editing the paper.

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Correspondence to Kelly Mahoney.

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Mahoney, K., Alexander, M., Thompson, G. et al. Changes in hail and flood risk in high-resolution simulations over Colorado's mountains. Nature Clim Change 2, 125–131 (2012).

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