Improve the projection of East China summer precipitation with emergent constraints

Abstract

Under global warming, summer precipitation over East China was projected to increase by current state-of-the-art climate models, but large inter-model spread exists. Here we try to reduce the projection uncertainty by imposing constraints. Our procedure consists of firstly decomposing the projected future precipitation into inter-model principal components. The two leading modes (region-wide uniform monopole and north-south dipole, accounting for 55% of variability), by emergent constraints, are then linked to the simulation of historical precipitation in the northwest Pacific and the tropical Pacific (constraining areas). This allows us to reduce the range of projected precipitation in East China by 24%, with a relatively uniform increase for the first mode and a larger increase in the north subregion for the second. It is also shown that the emergent relations of both modes are physically consistent, with an enhancement of future zonal land-sea thermal contrast and a La Niña-like pattern.