Preferential Hydrologic States and Tipping Characteristics of Global Surface Soil Moisture
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AbstractA dynamic transition in soil hydrologic states through meteorological variability and terrestrial feedback governssoilvegetationclimate (SVC) interactions, constrained by critical soil moisture (SM) thresholds. However, observational and scaling constraints limit critical SM threshold estimation at the remotesensing (RS) footprint scale. Using global surface SM (RS) from NASAs Soil Moisture Active Passive (SMAP) satellite, we characterize theseasonal preferential hydrologic states of RS and derive three tipping characteristics to estimate the intensity (Mean Tipping Depth, ), frequency (Tipping Count, ), and duration (Mean Tipped Time, ) of the excursion of RS from wet to dryaverage conditions. The preferential state provides the seasonally dominant hydrological states of RS, while tipping characteristics capture the ecosystem linkages of the dynamic transition in RS hydrologic states. Globally, RS predominantly exhibits a (unimodal) drypreferential state, especially over arid/semiarid drylands and a unimodal wetpreferential RS state in highlatitude boreal forests and tundra biomes. Prevalence of (bimodal) bistable RS state overlaps with regions of strong positive SMprecipitation coupling and monsoonal climate in semiarid/subhumid climates. Seasonal preferential hydrologic states covary with the regional variability in plant water stress threshold and landatmospheric coupling strength. Tipping characteristics of RS show sensitivity to intrabiome variability in SVC coexistence patterns and display high skill in partitioning global ecoregions. While and are climatecontrolled, is moderated by soil and vegetation through their influence over RS drydown during waterlimited evapotranspiration. Preferential states and tipping characteristics find applications in quantifying SVC coexistence patterns, climate model diagnosis, and assessing ecosystem sensitivity to climate change.
