Climate, soil, and vegetation controls upon the variability of water balance in temperate and semiarid landscapes: Downward approach to water balance analysis

Abstract

Observed differences between water balance for temperate and semiarid catchments can be attributed to variability in the primary controls of the soil profile (soil water storage capacity and permeability), vegetation (surface coverage and water use efficiency), and climate (rainfall and potential evaporation). Motivated by the downward development methodology mooted by Klemes [1983], this paper explores the underlying climate and landscape interactions that cause differences in water balance between a number of temperate and semiarid benchmark catchments around Australia. A systematic parsimonious analysis based around a simple water balance model whose parameters are estimated from available data is used to observe and interpret signatures of annual, intra-annual, and daily water balance behavior and variability. The essence of the downward analysis is that model complexity evolves from the simplest form to its final quasi-distributed framework with multiple storages and process interactions in response to inadequacies in signature prediction. Consequently, each step in the process develops insight into local climate and landscape influences and sensitivity to their temporal and spatial variabilities. The results affirm that the relative influence of climate and landscape properties upon catchment response is manifested in a systematic transformation of process sensitivity with increasing timescales (annual, monthly, daily, and hourly). Significantly, drier catchments are shown to be more sensitive to small-scale perturbation than humid catchments. We conclude that the downward analysis approach is a means to better understand the significance of landscape variability upon catchment response. Consequential knowledge can begin to explain data requirements and requisite model complexity and to provide insight into the ability to reliably predict water balance behavior. These are important first steps toward the longer-term objective of reliably predicting water balance variability across ungauged basins.