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Polar charts with 2000 most severe streamflow droughts from 1920 to 2020 that asks “when streamflow droughts occur?” Each chart shows the number of droughts by date with January at the top and moving clockwise through the year. The stacked colors of the bar chart represent decades from 1920s (center) to 2010s (outer). The CONUS polar chart demonstrates that not many droughts happen during the relatively wet spring months (March through June) when snowmelt and spring rains replenish streamflow.