Hydrological Responses To Rainfall Pulses In Desert Vadose Zones: A Multi-Scale Approach Integrating Geophysical, Isotopic, And Eddy-Covariance Measurements

Drylands are shaped by natural episodic precipitation, where short, intense rainfall pulses interrupt prolonged drought and drive most hydrological and ecological activity. Yet the mechanisms that determine how pulse water infiltrates, is redistributed, stored, evaporated, and ultimately used by desert vegetation remain under quantified in landscapes underlain by shallow petrocalcic horizons. This dissertation integrates three complementary approaches 1) three-dimensional electrical resistivity tomography, 2) eddy-covariance evapotranspiration partitioning, and 3) stable-isotope tracing to improve a mechanistic understanding of pulse-driven water movement and plant water use in a caliche-rich piedmont at the Jornada Experimental Range. The first component characterizes how infiltration pulses interact with variably cemented caliche. Time-lapse 3D imaging reveals rapid wetting followed by multi-day redistribution within the carbonate matrix, the formation of persistent subsurface storage zones, and a consistent inflection marking the transition between surface drying and deeper recharge. The second component examines how these soil-moisture dynamics shape atmospheric water exchange. By analyzing multi-year eddy-covariance records and applying the underlying water-use efficiency framework, the dissertation quantifies the sequence of post-pulse evapotranspiration responses. It identifies soil and climatic controls on the transition from evaporation- to transpiration-dominated fluxes. The third component utilizes a deuterium-enriched tracer to track the uptake of pulse water by plants, revealing contrasting species strategies, strong microsite effects imposed by caliche heterogeneity, and pronounced seasonal differences in the timing and persistence of water use. Together, these components show that shallow petrocalcic horizons modulate every stage of the pulse –response continuum, from infiltration and redistribution to evapotranspiration and plant uptake. By resolving when, where, and how water moves through the soil–plant–atmosphere system, this dissertation advances an integrated understanding of ecohydrological function in desert vadose zones and clarifies the mechanisms through which rainfall pulses sustain life in drylands.