21st Conference on Hydrology

6A.7

Global patterns of soil moistureŚrainfall relationships

Arien (H.A.) Lam, Utrecht University, Utrecht, Netherlands; and M. F. P. Bierkens and B. J. J. M. Van den Hurk

Many studies have demonstrated the dynamic role of terrestrial water in regional and global climate. Especially, relationships between soil moisture and rainfall receive a lot of attention. However, validation of feedbacks and other relationships between soil moisture and subsequent rainfall is problematic, both in a modelling context and in situ. Analysis of global patterns of feedback strength offers an extension of validation opportunities, as spatial climate patterns have been well-studied for a long time.

This study uses a generalized linear model to statistically analyze the probability of daily precipitation occurrence, dependent on precipitation persistence, annual cycle, and soil moisture. Strengths and weaknesses of this method will be discussed. When applying this method to a global reanalysis dataset (ERA40) spanning 45 years, patterns arise of the percentage deviance (a measure for variation) explained by each of the three variables.

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.

When comparing the magnitudes of explained deviance by each of the three variables, more patterns arise. In a surprisingly large part of the land surface, soil moisture influence on precipitation occurrence is in the same order of magnitude as the influence of the annual cycle. This indicates that soil moisture has a worldwide and profound impact on hydroclimate statistics.

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Session 6A, Land-Atmosphere Interactions 3
Thursday, 18 January 2007, 1:30 PM-4:30 PM, 209

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