  Observations of soil moisture (SM) during excess and deficit monsoon seasons
between 2000 to 2021 present a unique opportunity to understand the soil water
dynamics (SWD) over core monsoon zone (CMZ) of India. This study aims to
analyse SWD by investigating the SM variability, SM memory (SMM), and the
coupling between the surface and subsurface SM levels. Particularly intriguing
are instances of concurrent monsoonal extremes, which give rise to complex SWD
patterns. Usually, it is noted that a depleted convective activity and
persistence of higher temperatures during the pre-monsoon season leads to lower
SM, while monsoon rains and post-monsoon showers support the prevalence of
higher SM conditions. The long persistent dry spells during deficit monsoon
years enhances the Bowen ratio (BR) due to the high sensible heat fluxes. On
the other hand, the availability of large latent heat flux during excess
monsoon and post-monsoon seasons tends to decrease the BR. This enhancement or
reduction in BR is due to evapotranspiration (ET), which influences the SWD by
modulating the surface subsurface SM coupling. The surface and subsurface SM
coupling analysis for CMZ exhibits significant distinction in the evolution of
wet and dry extremes. SM variations and persistence time scale is used as an
indicator of SMM, and analysed for both surface and subsurface SM observation
levels. Evidently, subsurface SM exhibits remarkably prolonged memory
timescales, approximately twice that of surface SM. Furthermore, we dissect SWD
linked to wet and dry extremes by analysing annual soil water balance (SWB).
Our findings reveal augmented (diminished) ET during deficit (excess) years,
subjected to a higher (lower) number of break events. In essence, our study
underscores the significance of surface-subsurface SM observations in
unravelling the intricate tapestry of SWD.
