Greater North American Monsoon Precipitation Brought by Enhanced Storm Activity in a Warm Climate

<title>Abstract</title> <p> Climate models suggest a weakened North American summer monsoon (NAM) under elevated atmospheric CO ₂ , posing serious challenges to NAM region's socioeconomic development. This outlook is consistent with simulations of the mid-Pliocene (3.0 - 3.3 Ma), the closest analog to the middle-of-the-road future scenario. However, proxy evidence reveals enhanced summer precipitation in the monsoon region during the mid-Pliocene, raising questions about the climate projections. Here, we develop novel coupled high-resolution atmosphere-ocean simulations and utilize a feature tracking algorithm for mesoscale convective systems. Using these tools, we show that this summer precipitation enhancement reflects enhanced mesoscale convective system activity during the mid-Pliocene--an effect that emerges only in high-resolution simulations and results from land surface greening. These results highlight the importance of resolving surface albedo-moist convection interactions in modulating hydroclimate conditions in semi-arid continents, where the skill of climate hindcasts and projections are likely limited by model resolution. </p>