Evaluating the effects of precipitation and evapotranspiration on soil
moisture variability
Abstract
The effects of precipitation (Pr) and evapotranspiration (ET) on soil
moisture play an essential role in the land-atmosphere system. Here we
evaluate multimodel differences of these effects within the Coupled
Model Intercomparison Project Phase 5 (CMIP5) compared to Soil Moisture
Active Passive (SMAP) products in the frequency domain. The variability
of surface soil moisture (SSM), Pr, and ET within three frequency bands
(7 ~ 30 days, 30 ~ 90 days, and 90
~ 365 days) after normalization is quantified using
Fourier transform. We then analyze the impact of ET and Pr on SSM
variability based on a transfer function assuming these variables with a
linear time-invariant (LTI) system. For the simulated effects of ET and
Pr on SSM variability, models underestimate them in the two higher
frequency bands and overestimate them in the lowest frequency band but
show better estimates in transitional zones between dry and wet
climates. Besides, the effects on SSM by Pr and ET are found to be
different across the three frequency bands, and models underestimate the
one of Pr and ET as the dominant factor controlling SSM variability in
each frequency band. This study identifies the spatiotemporal
distribution of the CMIP5 model deficiencies in simulating ET and Pr
effects on SSM. Overcoming these deficiencies could improve the
interpretability and predictability of Earth system models in simulating
interactions among the three variables.