Abstract
Soil moisture impacts on precipitation have been strongly debated. Recent observational evidence of afternoon rain falling preferentially over land parcels that are drier than the surrounding areas (negative spatial effect), contrasts with previous reports of a predominant positive temporal effect. However, whether spatial effects relating to soil moisture heterogeneity translate into similar temporal effects remains unknown. Here we show that afternoon precipitation events tend to occur during wet and heterogeneous soil moisture conditions, while being located over comparatively drier patches. Using remote-sensing data and a common analysis framework, spatial and temporal correlations with opposite signs are shown to coexist within the same region and data set. Positive temporal coupling might enhance precipitation persistence, while negative spatial coupling tends to regionally homogenize land surface conditions. Although the apparent positive temporal coupling does not necessarily imply a causal relationship, these results reconcile the notions of moisture recycling with local, spatially negative feedbacks.
Highlights
Soil moisture impacts on precipitation have been strongly debated
Using this consistent analysis framework, we find that globally, afternoon rain is more likely at locations that are dry compared with the surrounding area, on days that are wet compared with the mean seasonal cycle, and on days with more heterogeneous soil moisture conditions than expected for a region and season
A precipitation event domain is defined as 5 Â 5 grid cells (0.25° Â 0.25° each, that is, 1.25° Â 1.25° in total) centred at a location of local afternoon precipitation maxima (Lmax) with at least 4 mm of accumulated rain
Summary
Soil moisture impacts on precipitation have been strongly debated. Recent observational evidence of afternoon rain falling preferentially over land parcels that are drier than the surrounding areas (negative spatial effect), contrasts with previous reports of a predominant positive temporal effect. 11 has recently suggested a strong dominance of negative coupling mechanisms in observations contrasting with a strong positive coupling in Global Climate Models This negative coupling could be consistent with negative indirect effects via soil-moisture-induced mesoscale circulations[5] or boundary-layer dynamics. Using this consistent analysis framework, we find that globally, afternoon rain is more likely at locations that are dry compared with the surrounding area (that is, negative spatial correlation), on days that are wet compared with the mean seasonal cycle (that is, positive temporal correlation), and on days with more heterogeneous soil moisture conditions than expected for a region and season These results demonstrate the coexistence of positive temporal and negative spatial relationships within the same region and based on the same data. We further propose physical mechanisms by which these apparently contradictory processes could coexist
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