Enhanced summer extreme precipitation over the Asian-African land monsoon regions during past warm periods: A modelling perspective from CESM2

Abstract

Investigation of summer extreme precipitation during past warm periods may deepen our understanding of its behavior in current and future warmer climates. In this study, we investigate the variation of summer (June-July-August) extreme precipitation and the associated dynamic mechanisms over the Asian and African land monsoon regions during the mid-Pliocene warm period (mPWP) and the Last Interglacial (LIG), using six extreme indices defined by the Expert Team on Climate Change Detection and Indices. Model results indicate that summer extreme precipitation becomes more intense and frequent over the African land monsoon region during both the mPWP and LIG relative to the pre-industrial, together with longer wet spell and shorter dry spell, though the magnitudes are relatively larger during the LIG than the mPWP. Based on the moisture budget equation, the vertical thermodynamic term and the vertical dynamic term largely account for the increased summer precipitation over the African land monsoon region during the mPWP and LIG, respectively. Over the Asian land monsoon region, summer extreme precipitation is also generally intensified and occurs more frequently during the mPWP and LIG, but with large regional differences. The main contributing factors to precipitation change hence vary greatly with sub-regions and periods. Although the modeled variations of extreme precipitation remain hard to be constrained by geological evidence, our results highlight an intensification of extreme precipitation in a warmer world, though the dominating factors (i.e., thermodynamic vs. dynamic) for precipitation change may vary with the external forcing that induces the warmth.