Hailfall in a future climate using a pseudo-global warming approach
Severe convective storms (SCS) and their associated hazards present significant societal risk however it is currently unclear how these storms may change in the future under anthropogenic climate change (ACC). Previous methods used to understand changes in SCS are limited by their coarse spatiotemporal resolution and representation of hail. To better understand why SCS and hail change, this study uses a pseudo-global warming (PGW) approach to simulate seven different historic hailstorms in their historical environments and again in PGW environments obtained from five different CMIP5 members. Changes in large-scale environmental parameters were generally found to be consistent with prior studies, showing increases in CAPE, CIN, and precipitable water, with minor changes in VWS. Nearly all simulated events had stronger updrafts in the PGW environments, even with increases in hydrometeor loading. However, only cold-season events showed an increase in hail sizes both within the storm and at the surface, whereas warm-season events saw a decrease in hail sizes at the surface and aloft. Changes in the hailfall area at the ground also showed a seasonal trend, with increases in cold-season events and decreases in warm-season events. Melting depths increased for all PGW environments and there is evidence that this increase contributes to greater area of rainfall for warm-season events where there is an increase in smaller hail aloft that would be more prone to melting. Further analysis of the changes in microphysical processes leading to hail for both warm- season and cold-season events was conducted to understand these differences. The PGW-warm- season events had an increase in the number of embryos in the hail growth zone which resulted in an increase in competition for growth and thus smaller hail sizes than in the simulations of the historical events. Paired with increases in melting depth, this led to a reduction in the area over which hail fell for future warm-season storms as compared to the historical simulations. PGW cold-season events, on the other hand, had similar numbers of, or even fewer, hail embryos in the hail growth zone than in the historical simulations, resulting in less competition for available supercooled liquid water and thus larger hail sizes. Because larger hailstones are less susceptible to melting, despite increased melting depths, the area of hailfall at the surface increased in future cold-season storms compared to the historical simulations. The results of this study thus suggest differing responses of warm-season and cold-season hailstorms to a future warmer climate. However, future work addressing more events in both seasons, including additional GCM projections of future environments, and developing a robust method to examine the production of hailstone embryos, are all warranted to establish the generality of this result and to pursue questions this work could not answer.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign