An Estimation of the Effect of Soil Moisture on Subsequent Precipitation
Using the SMOS Soil Moisture Product
Abstract
The nature of the relationship between soil-moisture and subsequent
precipitation is debated. Past studies have indicated that it varies by
location, but there have been disagreements on feedback sign, strength
and statistical significance over the same locations even while using
the same data sets due to differences in statistical approaches. Here we
re-evaluate estimates of feedback strength using Granger causality
(following Tuttle and Salvucci 20016) for SMOS and AMSR-2soil moisture
products and find that there is evidence both of there being a positive
feedback over the entire nation (SMOS) and of there being a west-to-east
gradient of positive to negative values (AMSR-2, similar to what was
found by Tuttle). This project has demonstrated that differences arise
using identical statistical estimation techniques with different
satellite estimates of soil moisture. The passive microwave AMSR-E and
AMSR-2 data produce a gradient of positive to negative impact factors
across the U.S. while the SMOS data set yields a mostly positive impact
factor over the entirety of the U.S. Here we explain this discrepancy by
noting that the areas where the sign of the impact differ are areas
where the soil moisture perturbations of SMOS and AMSR-2 are
anticorrelated, and also that these areas coincide with areas of high
vegetation cover, which are well known to challenge remote sensing
estimates of moisture.