Hysteresis Behaviors in East Asian Extreme Precipitation Frequency to CO2 Pathway

Abstract

Understanding regional hydro-climatic extreme responses to CO2 pathways is fundamental to climate change mitigation and adaptation. This study evaluates responses of extreme precipitation frequency (R30mm: days with precipitation >= 30 mm) over East Asia to idealized CO2 forcing using the Community Earth System Model (CESM1). Under a symmetric increase (ramp-up, +1% per year until quadrupling level) and decrease (ramp-down, about -1% per year back to the present level) of CO2 concentrations, East Asian R30mm shows an asymmetric response with higher frequency during the ramp-down period. This hysteresis behavior is found to be due to a northwestward propagating wave response to the El Nino-like warming, which induces a three-cell (positive-negative-positive) R30mm difference pattern from central equatorial Pacific to East Asia. Monthly analysis further reveals that this asymmetry has a seasonal locking, occurring during July-September only, constrained by the background precipitation climatology over the sub-tropical western Pacific.