Mesoscale convective systems over South America: Representation in km-scale climate simulations and future change

South America is highly vulnerable to storms and extreme precipitation. Mesoscale Convective Systems (MCSs), a prevalent storm type in tropical and subtropical South America, can be particularly damaging due to the organised, deep convection that fuels heavy precipitation over wide areas. Future warming will likely bring changes to MCS characteristics and precipitation extremes across the region. However, the relatively coarse spatial resolution of current regional climate models fails to explicitly resolve convective processes, making future changes to MCSs uncertain. Here, the representation of modelled MCSs is investigated in decade-long convection-permitting climate simulations over South America run by the UK Met Office. Changes to MCSs under global warming are then assessed using a future climate simulation. Simulated MCSs are tracked using a cloud tracking algorithm (tobac) and compared with those in satellite observations for seasonality, storm characteristics and regional differences. The simulations perform well at capturing the observed MCS climatology, including spatial frequency and seasonal cycle. However, the simulations overestimate MCS frequency over the Amazon Basin by a factor of 2 and underestimate MCS frequency over the La Plata Basin, likely due to a weak bias in the simulated South American Low-Level Jet.  In general, regional variations in MCS characteristics are also well simulated, but precipitation-related characteristics show larger model-observed differences. Simulated MCSs overestimate precipitation intensity and underestimate precipitation area. This results in an underestimation of the MCS contribution to total rainfall of 20-30% in the model, particularly in subtropical South America. The results from this work suggest that MCSs are generally well-captured by the CPM and have been used to inform results for future changes to MCSs over South America under climate change.