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WATER RESOURCES RESEARCH, VOL. 38, NO. 12, 1308, doi:10.1029/2001WR000824, 2002

Deep arid system hydrodynamics 1. Equilibrium states and response times in thick desert vadose zones

Michelle A. Walvoord

Earth and Environmental Science Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA


Mitchell A. Plummer

Earth and Environmental Science Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA


Fred M. Phillips

Earth and Environmental Science Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA


Andrew V. Wolfsberg

Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Abstract

Quantifying moisture fluxes through deep desert soils remains difficult because of the small magnitude of the fluxes and the lack of a comprehensive model to describe flow and transport through such dry material. A particular challenge for such a model is reproducing both observed matric potential and chloride profiles. We propose a conceptual model for flow in desert vadose zones that includes isothermal and nonisothermal vapor transport and the role of desert vegetation in supporting a net upward moisture flux below the root zone. Numerical simulations incorporating this conceptual model match typical matric potential and chloride profiles. The modeling approach thereby reconciles the paradox between the recognized importance of plants, upward driving forces, and vapor flow processes in desert vadose zones and the inadequacy of the downward-only liquid flow assumption of the conventional chloride mass balance approach. Our work shows that water transport in thick desert vadose zones at steady state is usually dominated by upward vapor flow and that long response times, of the order of 104–105 years, are required to equilibrate to existing arid surface conditions. Simulation results indicate that most thick desert vadose zones have been locked in slow drying transients that began in response to a climate shift and establishment of desert vegetation many thousands of years ago.

Published 20 December 2002.

Index Terms: 1866 Hydrology: Soil moisture; 1875 Hydrology: Unsaturated zone.

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Citation: Walvoord, M. A., M. A. Plummer, F. M. Phillips, and A. V. Wolfsberg (2002), Deep arid system hydrodynamics 1. Equilibrium states and response times in thick desert vadose zones, Water Resour. Res., 38(12), 1308, doi:10.1029/2001WR000824.