Precipitation variability encompasses attributes associated with the sequencing and duration of events of the full range of magnitudes. However, climate change studies have largely focused on extreme events. Using analyses of long-term weather station data, we show that high frequency events, such as fraction of wet days in a year and average duration of wet and dry periods, are undergoing significant changes across North America. Further, these changes are more prevalent and larger than those associated with extremes. Such trends also exist for events of a range of magnitudes. Existence of localized clusters with opposing trend to that of broader geographic variation illustrates the role of microclimate and other drivers of trends. Such hitherto unknown patterns over the entire North American continent have the potential to significantly inform our characterization of the resilience and vulnerability of a broad range of ecosystems and agricultural and socio-economic systems. They can also set new benchmarks for climate model assessments.

The multifaceted interface of plant roots, microbes, water, and soil can be considered a critical zone within the Critical Zone as it is host to many important dynamically linked processes, including the promotion of nutrient cycling through absorption and rhizodeposition, interaction and feedbacks with microorganisms and fungi, root‐facilitated hydraulic redistribution, and soil carbon dynamics. Such important processes in the Critical Zone have not been fully characterized and modeled in an ecohydrologic framework linking above‐ground natural and/or anthropogenic processes to below‐ground biogeochemical cycling. Specifically, the relation between root exudates and nutrient cycling remains an open challenge. Here we present the model REWT (Root Exudation in Watershed‐scale Transport) to demonstrate the systematic modeling of root exudation in an interconnected ecohydrologic framework. REWT incorporates an explicit dynamic root exudation transport model, nutrient absorption, and coupled microbial processes within the framework of a validated ecohydrologic model. Model simulations demonstrate the influence of root exudation of glucose, a polysaccharide that serves as fuel for microbes, and flavonoids, which can act as a biological nitrification inhibitor on microbial processes linked to soil carbon and nitrogen cycling. To demonstrate the capabilities of this theoretical framework, we parameterize REWT for corn and soybean crops in the Midwestern United States, and simulations indicate that rates of nitrification and respiration were substantially altered compared to model simulations in which root exudation was not explicitly included. This work demonstrates the importance of systematically incorporating root exudates into hydrobiogeochemical models and can serve to inform experimental design for active root zone processes.

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Process-based numerical modeling of shallow subsurface hydrobiogeochemistry, including root-microbe-soil interactions, has been a long-standing challenge (Vereecken et al., 2016). A model capable of describing ecohydrologic, vegetation, and geochemical dynamics is necessary to numerically resolve the link between vegetation processes, such as root exudation, reactive weathering products, and associated solute efflux from terrestrial environments (Sullivan et al., 2019). Such a framework could allow us to ask new questions about the effect of vegetation processes on long-term soil formation (Vereecken et al., 2016) and the role of land use changes on weathering of soil minerals (Barré et al., 2009;Céspedes-Payret et al., 2012). It could also allow us to examine the role of soil priming by roots to influence mineral-associated organic matter turnover (Jilling et al., 2018;Kleber et al., 2015) and the long-term resilience of soil organic matter and soil carbon stocks under future climate

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