By filtering the incoming climate signal when producing streamflow,
river basins can attenuate – or amplify – projected increases in
rainfall variability. A common perception is that river systems dampen
rainfall variability by averaging spatial and temporal variations in
their watersheds. However, by analyzing 671 watersheds throughout the
United States, we find that many catchments actually amplify the
coefficient of variation of rainfall, and that these catchments also
likely amplify changes in rainfall variability. Based on catchment-scale
water balance principles, we relate that faculty to the interplay
between two fundamental hydrological processes: water uptake by
vegetation and the storage and subsequent release of water as discharge.
By increasing plant water uptake, warmer temperatures might exacerbate
the amplifying effect of catchments. More variable precipitations
associated with a warmer climate are therefore expected to lead to even
more variable river flows – a significant potential challenge for river
transportation, ecosystem sustainability and water supply reliability.