Ecohydrological Optimality

S. J. SCHYMANSKI, A. KLEIDON AND M. L. RODERICK

(Submitted to Encyclopedia of Hydrological Sciences on 6 March 2008)

Abstract

Hydrological systems are governed by an incredible wealth of interactive processes, ranging from small-scale processes within the soil domain such as unsaturated flow, bioturbation and root water uptake to large-scale feedbacks between the water balance and the global atmospheric circulation. Optimality approaches aim towards a simpler and more general representation of hydrological systems. Since the hydrology on land is strongly affected by the presence of vegetation, these optimality approaches generally need to be explored in the context of how purely hydrological processes are linked to ecological processes. This article summarises the different optimality assumptions that have been used to describe ecohydrological processes and how these are related to each other. Most approaches can be classified as either physical or ecological optimality. A range of examples are given for applying optimality approaches at various temporal and spatial scales, ranging from the scale of individual leaves and how they control water loss in relation to carbon uptake to the larger-scale attributes of vegetation types, ecosystem properties and river basin networks. The article closes with a discussion of the usefulness of optimality approaches and their advantages, but also their disadvantages and needs for improvement.