Abstract
Understanding the global soil moisture (SM) dynamics and its governing
controls beyond Darcy Scale is critical for various hydrologic,
meteorological, agricultural, and environmental applications. In this
study, we parameterize the pathways of the seasonal drydowns using
global surface soil moisture (θ_RS) observation from SMAP satellite
(between 2015 and 2019) at 36km X 36km. We develop a new data-driven
non-parametric approach to identify the canonical shapes of θ_RS
drydown, followed by a non-linear least-squares parameterization of the
seasonal drydown pathways at each SMAP footprint. The derived parameters
provide the effective soil water retention parameters (SWRPeff),
land-atmospheric coupling strength, soil hydrologic regimes for SMAP
footprint. Depending on footprint heterogeneity, climate and season, the
characteristics curves comprising different drydown phases are
discovered at SMAP footprints. Drydown curves respond to the
within-footprint changes in the meteorological drivers, land-surface
characteristics and the soil-vegetative and atmospheric dynamics.
Drydown parameters display high inter-seasonal variability, especially
in grasslands, croplands and savannah landscapes due to significant
changes in the landscape characteristics and moisture patterns at the
subgrid-scale. Soil texture exert influence on the characteristics soil
water retention and drydown parameters only when the footprint mean
θ_RS is low, specifically in arid and sparsely vegetated regions. The
influence of soil texture on the inter-seasonal variability of SWRPeff
is low compared to landuse and climate at RS-footprint scale. The global
understanding of characteristics SM drydown features at SMAP footprints
provides a significant step towards a scale-specific, effective soil
hydrologic parameterization for various applications.