Talk by Allen G. Hunt, Wright State University: A critical journey into the Critical Zone

Topic: Hydrology

Dr Allen Hunt Seminar Speaker

When

Noon – 1 p.m., Nov. 1, 2023

Where

Available remotely via Zoom
Seminar Format

Available remotely only via Zoom webinar. Contact the department to subscribe to the email list (zoom link provided in announcement).

Abstract

A spatiotemporal scaling relationship that yields soil depth as a function of time has been shown in multiple publications to give accurate predictions of soil depth, in many cases, without using any unknown parameters. Temporal differentiation and setting equal to the erosion rate yields a steady-state soil depth (Jenny's sol forming factors equation) in terms of the infiltration water flux, verified in multiple publications. Another series of publications verify a second scaling relationship for the temporal and spatial dependence of growth rates of vegetation, as well as the dependence of net primary productivity NPP on the transpiration flux. Approximating the transpiration by evapotranspiration, ET, and the infiltration by run-off, Q, allows maximization of NPP with respect to the optimal partitioning of water at the terrestrial Earth surface into ET and Q, since NPP is proportional to both the lateral growth and the soil depth, whereas these two fluxes sum to precipitation, P. The value obtained is, using only universal parameters from percolation theory, within 1.5% of the global average. Results for P - ET = Q as functions of climate variables are accurate enough to generate the observed streamflow elasticity across studies at global scales and reproduce "the principal features of catchments," "allowing prediction of the interplay between climate, soil and vegetation under conditions of climate change." (Eos, August 2023). 

Further benefits include the ability to predict NPP and species richness as a function of climate variables. The results for ET as a function of climate variables match the best-fit function for global data from FLUXNET (Williams et al., 2012), as well as those with the largest ET from vegetation optimality of a dynamic process model published subsequently in HESS. Finally, the strategy used to calculate ET and NPP is virtually identical to the process outlined in "Opportunities in the Hydrologic Sciences," the NAS-commissioned report justifying the founding of NSF's Hydrologic Sciences program.
Bio

Allen Hunt received a Ph.D. in theoretical physics from the University of California, Riverside, in 1983 in the area of transport in disordered systems, specifically applying percolation concepts.

From 1985-1987, he continued research in this general field with applications to, e.g., the photoconductivity of amorphous silicon at Phillips University, Marburg, Germany, as a Fulbright Scholar. In 1992, he began his interest in subsurface hydrology and soil physics in stochastic hydrology and hydraulics (perturbation theory), working with Zbigniew Kabala. In 1996, he received an M.A. in field geomorphology with Peter Haff at Duke University, addressing hillslope erosion processes. From 1999-2002, he was a visiting scientist in climate dynamics at the Pacific Northwest National Laboratory. From 2002-2003, he was program director in hydrologic sciences at the USA National Science Foundation. In 2004, he began his employment at Wright State University, where he continues today. He has published five books, including Percolation Theory for Flow in Porous Media, Lecture Notes in Physics (three editions, Springer), Networks on Networks: The Physics of Geobiology and Geochemistry (Institute of Physics, UK), and Hydrogeology, Chemical Weathering, and Soil Formation (AGU/Wiley). His research has addressed the fundamental physics of flow, solute transport, reaction, vegetation growth, and, most recently, the water cycle.
Bio

Allen G. Hunt: [Email: allen.hunt@wright.edu | Google Scholar]

Seminar

Contacts

Bo Guo, Host
boguo@arizona.edu