The dynamical signature on the change of hydrological extremes under global warming

Abstract:

The increased water vapor content due to climate warming can impact the global hydrological cycle not only by the direct thermodynamic effect constrained by the Clausius-Clapeyron relation, but also impinging on features of circulation through coupling with the atmospheric dynamics. Through implementing the concept of finite-amplitude wave activity (FAWA) and its three-dimensional extension to local FAWA, the increase of the hydrological extremes manifested in terms of FAWA under climate change scenario RCP8.5 can be decomposed into the part due to the background increase of moisture (scaled with the temperature warming, thus representing thermodynamical effect) and the part due to the change of waviness of the contours of moisture (representing the dynamical factor). It is found that the both thermodynamical increase of moisture and the change of the waviness project on to the enhancement of the climatological pattern of the FAWA associated with the poleward moisture intrusion (Am). Whereas, the change of the FAWA associated with the dry air intrusion (Ad) is characterized by both an enhancement of the background pattern and a poleward expansion thereof, the latter arising from the poleward shift of the wavy motion. This result may serve as a rationale for why both dry and wet extremes will become more frequent while the time mean temperature and water vapor increase under global warming. The relative contributions to the response of the waviness in the moisture distribution from the stationary wave versus the transient waves will also be examined.