Changing Duration and Spatial Extent of Mid-latitude Extreme Precipitation Events Across Different Climates

The intensity of extreme precipitation is widely expected to increase with global warming, but changes in the duration of extreme precipitation events are less clear. Here we use an event-based metric to quantify the duration and spatial extent of extreme precipitation events in climate model simulations. We link the duration to an advective time scale in the mid-latitudes: L/U, where L is the zonal length of the precipitation events (calculated in the same way as the duration, except in longitude rather than time), and U is the zonal wind speed. Using a comprehensive GCM, we find that the duration decreases by a small percentage across the mid-latitudes with warming. In the Northern Hemisphere, one might expect a weaker low-level meridional temperature gradient due to Arctic Amplification to reduce the zonal wind speed and lead to longer duration precipitation extremes. But the reduction in wind speed is small and instead the duration decreases because of a decrease in the zonal length of the precipitation extremes. We also investigate how the duration changes in an idealized GCM across climates with different meridional gradients of solar insolation. In these simulations, the zonal wind speed changes are larger and climates with faster zonal winds have shorter duration extreme precipitation events. The zonal length scale of the events increases with increasing meridional temperature gradient but at a slower fractional rate than the zonal wind. Thus we find that the advective time scale gives insights into the factors controlling the duration of precipitation extremes in mid-latitudes.