Deciphering the Drivers Favorable for Summer Monsoon Precipitation
Extremes over the Indian Himalayas
Abstract
This study investigates the physical processes behind extreme
precipitation events (EPEs) in the Himalayas, notorious for causing
frequent floods and significant loss of life and property. Due to the
presence of complex terrain, understanding the driving factors behind
these EPEs has proven challenging. Here, we decipher the driving
conditions responsible for the occurrence of EPEs in the western
Himalayas (WH) for the period 1979 to 2020. Our findings provide
compelling evidence for the role of large-scale circulation patterns and
their associated dynamics and thermodynamics in instigating EPEs. The
presence of distinct upper-tropospheric gyres flanking the WH, alongside
a prominent zonal wave pattern, underscores the conducive atmospheric
configuration during EPEs. This configuration promotes a southward
extension of the trough, intensifying the convergence of moisture-laden
winds from the adjoining seas, leading to substantial moisture
availability for the EPEs. Moreover, the southward advancement of
cyclonic vorticity further aids in northward moisture advection towards
the region. At a regional scale, using moisture budget analysis, we find
that vertical moisture advection plays a significant role, emphasizing
the dominance of local dynamics driving these EPEs. Furthermore, the
intensifying diabatic heating structure over the WH leads to intensified
convection through stronger vertical motions, facilitating the
development of deep convection. Our results also pinpoint the role of
the shifting of the Intertropical Convergence Zone (ITCZ), strongly
linked to the dynamics of convective clouds, resulting in changes in the
intensity of EPEs over the WH. Additionally, Quasi-Resonance
Amplification is linked with the most intensified/persistent EPEs over
the Himalayas.