Heavy precipitation is highly sensitive to the magnitude of future warming

Abstract

Heavy precipitation exerts strong societal and economic impacts, including flooding, and these precipitation events are projected to increase under anthropogenic warming. The United Nations Framework Convention on Climate Change (UNFCCC) Paris Agreement signed in December 2015 aims to limit the global average temperature rise to below 2 °C above preindustrial levels, with an added goal of limiting temperature increases to 1.5 °C. There remains a major knowledge gap related to our understanding of changes in heavy precipitation under the 1.5 and 2 °C warming targets. Here, we investigate the changes in heavy precipitation events with the Community Earth System Model (CESM) climate experiments using the scenarios consistent with the 1.5 and 2 °C temperature targets. We find that the frequency of annual heavy precipitation at a global scale increases in both 1.5 and 2 °C scenarios until around 2070, after which the magnitudes of the trend become much weaker or even negative. Overall, the annual frequency of heavy precipitation across the globe is similar between 1.5 and 2 °C for the period 2006–2035, and the changes in heavy precipitation in individual seasons are consistent with those for the entire year. The frequency of heavy precipitation in the 2 °C experiments is higher than for the 1.5 °C experiment after the late 2030s, particularly for the period 2071–2100. While the results of both experiments indicate that the warming targets in the Paris Agreement, if met, would be effective in reducing the frequency of heavy precipitation (2 °C target minus 1.5 °C target), they also suggest a lower risk of global heavy precipitation under the 1.5 °C target of about 33% for the period 2071–2100.