The partitioning of precipitation into interception, throughflow, infiltration, storage, evaporation, sublimation, transpiration, recharge, runoff, and stream flow is intimately linked to critical zone structure. Water stores and fluxes are both drivers of CZ evolution and a function of CZ development with feedbacks between vegetation, soil, landform, and bedrock. Within the EEMT framework that unifies work on the JSC CZO, water is a both direct driver of CZ development and an indirect driver that constrains carbon cycling and chemical energy for weathering reactions. Hydrologic flow paths also feedback to affect vegetation structure, microbial community development, soil formation and hydraulic characteristics, landform morphology, mineral surface areas, and carbon transport. Our EHP theme is designed to quantify these multi-scale and multidisciplinary linkages between the water cycle and CZ evolution.

Current research foci include:

• Quantifying spatial and temporal variability in total precipitation inputs, including rain and snow
• Quantifying spatial and temporal variability in sublimation and net snow water inputs
• Identifying water sources for vegetation
• Understanding species differences in water use and response to changes in precipitation
• Identifying feedbacks between vegetation structure and evaporation vs transpirative fluxes
• Quantify topographically-driven hydrologic subsidy (or deficit) and Effective Precipitation (Peff) available to plants
• Quantifying spatial and temporal variability in GPP, NEE, and soil carbon inputs
• Quantifying the sensitivity of soil respiration to changes in climate, especially water availabilit

Observations range in scale from individual trees, plots, and hillslopes in our intensively studied ZOBs, to eddy covariance towers that capture water and carbon fluxes at ~1km², to airborne and space-based remote sensing of vegetation and hydrologic states.

Similar to much of the western US, snow is a critical driver of CZ evolution in both the JRB and SCM sites and significant efforts have been made at understanding the distribution and fate of seasonal snowpacks.

Snow cover typically is ephemeral at our SCM sites accumulating and ablating multiple times over the course of a typical winter.  In contrast, snow cover typically is continuous from late November through mid April at our JRB sites.   Although seemingly subtle, this difference between the sites has significant effects on soil frost, hydrologic partitioning, carbon cycling and nutrient availability that are being explored by CZO students.