Global patterns of relations between soil moisture and rainfall occurrence in ERA-40

Abstract

We use a generalized linear model to statistically analyze the probability of daily precipitation occurrence, dependent on precipitation persistence, annual cycle, and soil moisture. By applying this method to the global ERA-40 re-analysis data set, we reveal patterns of the precipitation occurrence variability as explained by each of the three variables and their interactions. These global patterns show: (1) known monsoon regions dominate the annual cycle component; (2) known regions of orographic uplifting dominate the persistence component; (3) the soil moisture component shows structure across all continents, but is most pronounced in the tropics and subtropics, and least pronounced in polar regions. In a surprisingly large part of the land surface, soil moisture influence on precipitation occurrence is of the same order of magnitude as the influence of the annual cycle. Copyright 2007 by the American Geophysical Union.