Intensification of hourly and Small watershed flooding with rising temperatures

Abstract

Global warming has increased intensity of extreme precipitation events, and it is expected that the intensity of resulting floods will also rise, especially as intensified short-duration extreme precipitation may exacerbate dangerous flash floods. However, quantitative evidence remains limited, and existing research tends to focus on large river basins. Here we analyzed and compared how hourly extreme precipitation and streamflow in the Yangtze River Basin and its tributaries respond to temperature changes using scaling analysis. Our findings reveal a consistent temperature response across different spatial scales in the basins: hourly extreme precipitation increases at approximately 1.75 times the rate of daily precipitation. Furthermore, floods show a positive response to rising temperatures, but the degree of this response is more consistent in the mainstem than it is in the tributaries. Both daily and hourly extreme streamflow in the mainstem increases by about 7 % (7.47 % and 6.18 % respectively) for every 1 °C increase in temperature. Notably, the increase in hourly extreme streamflow is less pronounced than that in hourly precipitation intensity, likely moderated by reservoirs and the various factors influencing flood formation. In contrast, hourly extreme streamflow in most tributaries increases by 14 % or more. These findings highlight that hourly extreme precipitation and flood responses in smaller watersheds significantly exceed thermodynamic expectations, increasing flash flood risks and posing challenges for flood mitigation.