Journal of Earth Science & Climatic Change
Open Access

Abstract

Statement of the Problem: The anticipated increase in the frequency and severity of droughts across the globe will intensify water stress on terrestrial ecosystems and hence on food security. Regional land surface and global climate models largely rely on satellite remotely sensed surface soil moisture (typically the top 5 cm of the soil) to predict vegetation response (carbon uptake) to water stress or otherwise to characterize land surface fluxes. Ideally, however, the deeper soil layer root-zone moisture reflected by nighttime vegetation water content is the correct measure of such feedbacks. Differences in rooting depth and vegetation plant functional types (crops, forests, grasslands, etc.) also play an important role in dictating where and when the fluctuations in vegetation water content can be more predictive of carbon fluxes than the surface soil moisture. Methodology & Theoretical Orientation: In this study, we compile global data sets of surface soil moisture, vegetation water content and global carbon fluxes from satellite remote sensing (NOAA��?s AVHRR) spanning the years 2002 to 2010. The data is at high temporal (daily) and spatial (0.25o�?�?0.25o) resolution allowing the analysis to extend to multiple time scales. The correlation structure between surface soil moisture and/or vegetation water content with global carbon uptake is analyzed across all climatic regimes and plant functional types across the globe. The statistics of mutual information content across several plant physiologic response mechanisms, commonly referred to as isohydric vs. anisohydric response is also examined. Findings: The preliminary results indicate that the tropics (e.g., Amazonia), dominated by isohydric shallow root plants, tend to exhibit weaker dependence on water content than higher latitudes with generally vegetation water content having stronger correlation with carbon fluxes. Isohydric plant species show less dependence on shallow soil moisture, while fluctuations in daytime vs. nighttime vegetation water content have strong correlation with anisohydric species��? response. Conclusion: This study improves the predictability of global carbon fluxes and proposes the incorporation of vegetation water content as a reliable surrogate of shallow soil moisture in global models.

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