Characterization of the Coherence Between Soil Moisture and Precipitation at Regional Scales

Knowledge of the interplays between soil moisture (SM) and precipitation (P) across different temporal scales is crucial to understand the land-atmosphere interactions. To examine the factors influencing SM-P coherences, observed long-term SM and P datasets were obtained from two regional networks (i.e., the Nebraska Mesonet and part of the Soil Climate Analysis Network in Utah) within the continental United States. We evaluated the intricate SM-P interactions by checking high- and low-frequency components using wavelet analysis. The analysis revealed that the global coherence coefficients (GCCs) between SM and P at all frequencies tended to be greater under wetter climatic conditions, suggesting that higher P could promote the SM-P interactions. Moreover, GCCs were more correlated with meteorological factors in Nebraska with wetter climates (e.g., positively with mean annual P and negatively with aridity index at high-frequency periodicities (daily to 3 monthly), and opposite interactions at low-frequency periodicities (3 monthly to yearly); whereas, significant correlations emerged between GCCs and soil texture at all frequency periodicities in Utah (e.g., positively with sand fraction while negatively with silt and clay fractions). Part of the reason for the impact of soil texture in Utah was that as the P periodicities weakened with increasing climatic dryness in Utah, soil texture played a more important role in controlling infiltration processes, which directly affected SM-P coherences. Overall, this study demonstrates that SM-P interactions at regional scales were possibly affected by the relative importance of meteorological and local land surface conditions in controlling SM dynamics. Key Points The SM-P interactions are evaluated by checking high- and low-frequency components using wavelet analysis Global coherence coefficients (GCCs) between SM and P at all frequencies tend to be greater under wetter climatic conditions The SM-P interactions at regional scales are determined by the relative importance of P and soil texture in controlling SM dynamics