Robust simulation of root zone soil moisture with assimilation of surface soil moisture data

TLDR

The study builds on the widely used ISBA force‑restore soil‑vegetation‑atmosphere transfer model. It presents an operational framework for assimilating surface soil‑moisture remote‑sensing data into an SVAT model to robustly predict root‑zone moisture time series. The framework analytically couples surface and deeper soil reservoirs, using biases between observed and modeled surface‑moisture rate‑of‑change to infer root‑zone moisture biases, and is evaluated on a 183‑day Cork, Ireland dataset and four shorter hydrometeorological periods. The framework remains robust across three orders of magnitude of saturated hydraulic‑conductivity misspecification and, under uncertain initial conditions, markedly improves model skill over the baseline ISBA model during periods of precipitation below potential evaporation.

Abstract

An operational framework is presented for assimilating surface soil moisture remote sensing measurements into a soil‐vegetation‐atmosphere‐transfer (SVAT) model for the robust prediction of root zone moisture time series. The proposed approach is based on analytical treatment of the dynamical equations coupling surface and deeper soil reservoirs. The resulting framework uses biases between observed and modeled time rates of change of surface soil moisture to quantify biases between modeled and actual root zone average soil moisture contents. The approach is based on the popular interactions between soil‐biosphere‐atmosphere (ISBA) force‐restore SVAT model. An experimental data set, collected near Cork, Ireland, is analyzed both for a long data series of 183 days and four short periods that were selected to focus on different hydrometeorological conditions. The results demonstrated that the proposed framework performs uniformly robust over 3 orders of magnitude of misspecification of saturated hydraulic conductivity. In the presence of uncertain initial conditions, the results demonstrated a marked increase in model skill (over the original ISBA model) for periods when average precipitation was less than average potential evaporation.