SPRING WARMING DRIVES PAST AND FUTURE SHIFTS IN GREAT PLAINS STORM INTENSITY

Mesoscale convective systems (MCS) account for ~70% of warm-season rainfall over the Great Plains. These systems are often accompanied by severe weather and flooding, causing billions of dollars in economic losses annually. However, the processes driving variability in MCS activity are still debated, limiting our ability to predict future changes in hydroclimate and extreme weather for much of the central US. Here, we report a multi-proxy record of past MCS activity and hydroclimate variability from central Texas. Our results indicate lower-than-today storm activity at the Last Glacial Maximum, a rapid shift towards more stormy conditions at ~14 ka, and extremely low storm activity in the mid-Holocene. Using transient climate model simulations, we find that changes in storm activity and hydroclimate in the southern Great Plains over the last 20,000 years were dominated by changes in the strength of the Great Plains Low-Level Jet, driven by springtime land surface temperature changes. These results suggest that a similar dynamical response to future warming will lead to enhanced MCS activity and an increase in extreme weather and flooding across the southern and central Great Plains in the future.