The Tarrawarra project: high resolution spatial measurement, modelling andanalysis of soil moisture and hydrological response

Detailed spatial patterns of soil moisture were measured for 13 dates at th e 10.5 ha Tarrawarra catchment in southern Victoria, Australia. Several ana lyses of the data are summarized. These include: hydrological behaviour, in cluding preferred states, spatial organization and the performance of terra in indices; geostatistical properties of the soil moisture patterns; and re mote sensing of the soil moisture patterns. In the second part of the paper , the patterns along with surface runoff and meteorological data are used i n applications of the Thales and VIC models at Tarrawarra. Thales is a proc ess-based distributed parameter hydrological model which explicitly simulat es the spatio-temporal patterns of soil moisture, while VIC uses a lumped s tatistical distribution approach to model the spatial variability of soil m oisture storage. Both models simulate saturation excess runoff and are forc ed by rainfall and potential evapotranspiration. VIC was calibrated to obse rved runoff at the catchment outlet. Limited manual calibration of Thales t o runoff and the soil moisture patterns was performed. Internal testing was achieved by comparison of predicted and observed spatial soil moisture pat terns for the Thales model and of predicted and observed cumulative distrib utions of active soil moisture storage for the VIC model. With limited cali bration effort, Thales was able to to simulate the seasonal changes in char acteristics of the spatial soil moisture patterns. Detailed examination of the errors in the simulated patterns allowed identification of structural p roblems in the model, including problems with simulating lateral redistribu tion as the catchment wets in autumn. For the VIC model, time-series of spa tially averaged internal state variables (total storage) were consistent wi th observations. However, the statistical distribution of soil moisture sto rage assumed in the model differed from that observed. The collection of de tailed spatial data for soil moisture patterns provided a basis for testing the internal states relevant to each model formulation (spatially distribu ted for Thales and statistically lumped for VIC), as well as improving the identification of the dominant runoff processes. Copyright (C) 1999 John Wi ley & Sons, Ltd.