Topic: Simplifying and Improving an Integrated Theory of the Catchment to Predict the Water Balance

Speaker: Dr.  Allen Hunt

Time: 10：00-12:00am June 18, 2025

Venue: Meeting Room A901, IGSNRR

Brief Introduction to the report:

Catchment science has three interrelated components: 1) the shape of the land surface, which collects the water, 2) plants that use water to produce biomass, and 3) the water itself, which changes the land, creates soil, and feeds the plants.

Using inadequate theory leads to degraded predictions. While surface water flow only erodes a catchment, subsurface water flow is the basis for plant transpiration as well as soil formation. Solutes carried along these flow paths and the growth of the plants themselves follow rates that are slower than water flow, guided by paths of minimum resistance. The science that best describes these paths is called percolation theory (PT).

Scaling relations from PT yield expressions for soil depth and plant growth in terms of the complementary (i.e., they sum to P) fluxes, ET and Q. Since plants cannot grow without water, but can scarcely grow without soil, there is a partitioning of P between soil and plants that maximizes plant productivity.

The hypothesis that plants have actually evolved to exploit this maximum, provides an ecological basis for solving the water balance with all its associated benefits. These include improved predictions of streamflow elasticity as well as tree species richness in terms of net primary productivity. In their investigations, the predictions for streamflow elasticity were sufficiently accurate to generate predictive results for the dominant influences on drainage basin storage across scales from a few square kilometers to the world's largest drainage basins.

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