David A. Post

Predicting the daily streamflow of ungauged catchments in S.E. Australia by regionalising the parameters of a lumped conceptual rainfall-runoff model

Deriving relationships between catchment-scale hydrologic response and landscape attributes allows the hydrologic response of an ungauged catchment to be predicted from its landscape attributes and climate. In this study, a lumped conceptual rainfall-runoff model was applied at a daily timestep to 16 small (less than 1 km 2 ) catchments in the Maroondah region of Victoria, Australia. The six parameters of this model can be used to characterise the daily streamflow of the catchments. It was demonstrated in Post and Jakeman (1996) [Post, D.A., Jakeman, A.J., 1996. Relationships between catchment attributes and hydrological response characteristics in small Australian mountain ash catchments. Hydrol. Processes 10: 877‐892] that these six parameters are related to the landscape attributes of the catchments. In the current paper, these relationships are quantified and used to predict the daily streamflow of each catchment from its landscape attributes and daily rainfall and temperature, as if it were ungauged for streamflow. This predicted streamflow is then compared with the observed streamflow of the catchment. These relationships may also be used to predict the daily streamflow from other, similarly sized catchments in the Maroondah region. Some of the relationships between the model parameters and landscape attributes are well defined, while others are quite poor. As a result, the predictions of daily streamflow also vary in quality. Improvement of these results can be obtained through better understanding of the controls on hydrologic response.

An improved methodology for predicting the daily hydrologic response of ungauged catchments

In order to model fluxes of water from the land surface to the atmosphere, and from one grid cell to another in climate models, predictions of hydrologic response are required for catchments where hydrologic data are not available. A methodology has been presented previously that has the capability of producing estimates of catchment scale hydrologic response for ungauged catchments on a daily timestep (Post and Jakeman, 1998, Ecol. Mod. submitted). In the present paper, it is demonstrated that these daily predictions of hydrologic response can be improved by incorporating information about the hydrologic response of the catchment on a longer timestep. This is because the influence of large scale phenomena such as climate and vegetation may produce a similar water yield in nearby catchments, even though their daily hydrologic response may be different, due for example, to differences in drainage density. Thus, the water yield of an ungauged catchment is inferred on an inter-annual timestep, and this information is used to balance the water budget of a daily timestep rainfall-runoff model. It was found that using tree stocking densities to predict water yields for small experimental catchments in the Maroondah region of Victoria produced better results than those obtained by inferring the water balance parameter of a daily timestep rainfall-runoff model from channel gradient and catchment elongation. Good predictions of inter-annual water yield were also obtained for small experimental catchments in the H. J. Andrews, Hubbard Brook, and Coweeta long term ecological research (LTER) sites in the United States, indicating that it may be possible to produce high quality predictions of daily hydrologic response for ungauged catchments in these regions also.

Rainfall-runoff Modelling across Southeast Australia: Datasets, Models and Results

Abstract This study describes a daily rainfall, potential evaporation and streamflow data set compiled for the important water resources region of southeast Australia, and the application of six commonly used lumped conceptual rainfall-runoff models to estimate daily runoff across the region. The daily climate data set and the daily modelled runoff are available from 1895 to 2008 at 0.05° grid resolution across the region. The modelling exercise indicates that the rainfall-runoff models can generally be calibrated to reproduce the daily observed streamflow (for 232 catchments in the high runoff generation areas), and the regionalisation results indicate that the use of optimised parameter values from a gauged catchment nearby can model runoff reasonably well in the ungauged areas. There are differences between the six models, but they are relatively small when used to describe aggregated results across large regions.

Observed hydrologic non-stationarity in far south-eastern Australia: implications for modelling and prediction

The term ‘hydrologic non-stationarity’ has been used to describe many things, ranging from different climate-runoff relationships evident in different periods within a long hydroclimate time series to changes in hydroclimate characteristics and dominant hydrological processes in an increasingly warmer and higher CO2 world. This paper presents several examples of observed ‘hydrologic non-stationarity’ in far south-eastern Australia exposed by the prolonged 1997–2009 “Millennium” drought, focussing on the implications of this hydrologic non-stationarity on hydrological modelling and prediction. The runoff decline during the drought was unprecedented in the instrumental historical record. It was caused not only by the lower annual rainfall, but also by changes in other climate characteristics (lack of any high rainfall years, change in rainfall seasonality and higher temperatures) and dominant hydrological processes (reduced surface–groundwater connection and farm dams intercepting proportionally more water during dry periods). Hydrological models developed and calibrated against pre-1997 data cannot predict adequately the flow volumes and runoff characteristics during the drought. However, as the Millennium drought has exposed these extreme conditions, models can now be developed and calibrated to represent these, as well other conditions observed in the instrumental historical records (i.e., hydrologic non-stationarity that has already been observed). Such models should be able to satisfactorily predict the near-term runoff which will be influenced mainly by the rainfall inputs. However, further into the future, runoff will be increasingly influenced by higher temperatures and changed ecohydrological processes under higher CO2. Reliably modelling these is difficult because of the complex interactions and feedbacks between many variables and processes in a future environment not seen in the past (i.e., hydrologic non-stationarity that has not been observed).

Hydrologic regimes of forested, mountainous, headwater basins in New Hampshire, North Carolina, Oregon, and Puerto Rico

This study characterized the hydrologic regimes at four forested, mountainous long-term ecological research (LTER) sites: H.J. Andrews (Oregon), Coweeta (North Carolina), Hubbard Brook (New Hampshire), and Luquillo (Puerto Rico). Over 600 basin-years of daily streamflow records were examined from 18 basins that have not experienced human disturbances since at least the 1930s and in some cases much longer periods. This study used statistical methods to systematically evaluate the relationship between precipitation and streamflow at a range of spatial and temporal scales, and draw inferences from these relationships about the hydrologic behavior of the basins. Basins in this study had fundamentally different abilities to store and release moisture at a range of time and space scales. These different hydrologic regimes are the result of different types of forest canopies, snow, and soils in the study basins. Through their influences on interception and transpiration, forest canopies appear to play a very important role in the hydrologic regimes at Andrews and Luquillo, but at Coweeta and Hubbard Brook, the current deciduous forest plays a more limited although seasonally important role. Because of the timing of melt and its interaction with soils, seasonal snowpacks at Hubbard Brook and Andrews have quite different effects upon streamflow and vegetation water use. A variety of water flowpath types in soil, from macropore flow to long flowpaths in deep soils or fractured bedrock, appear to operate at the four sites. Hydrologic regimes may help predict the temporal scales of biogeochemical cycling and stream ecological processes, as well as the magnitude and timing of hydrologic response to disturbance and climate change in headwater basins.

Conceptual Rainfall–Runoff Model Performance with Different Spatial Rainfall Inputs

AbstractDifferent methods have been used to obtain the daily rainfall time series required to drive conceptual rainfall–runoff models, depending on data availability, time constraints, and modeling objectives. This paper investigates the implications of different rainfall inputs on the calibration and simulation of 4 rainfall–runoff models using data from 240 catchments across southeast Australia. The first modeling experiment compares results from using a single lumped daily rainfall series for each catchment obtained from three methods: single rainfall station, Thiessen average, and average of interpolated rainfall surface. The results indicate considerable improvements in the modeled daily runoff and mean annual runoff in the model calibration and model simulation over an independent test period with better spatial representation of rainfall. The second experiment compares modeling using a single lumped daily rainfall series and modeling in all grid cells within a catchment using different rainfall inp...

Modelling sources of sediment at sub-catchment scale: An example from the Burdekin catchment, North Queensland, Australia

A detailed sediment budget has been derived for the Weany Creek sub-catchment (13.5km^2) in North Queensland, Australia, using a sediment source, transport and depositional model known as SedNet (I. Prosser, P. Rustomji, W. Young, C. Moran, A. Hughes, CSIRO Land and Water Technical Report 15/01, Constructing River Basin Sediment Budgets for the National Land and Water Resources Audit, 2001, http://www.clw.csiro.au/publications/technical2001/tr15-01.pdf.). In this study, we have applied SedNet at a much finer scale than it has been applied previously in order to determine sources and sinks of sediment at a scale suitable for grazing land management. We have been able to show that a model such as SedNet can be applied to finer scales (with scale-appropriate modifications to inputs) and in so doing provide insight into sources and sinks of sediment at sub-catchment or paddock scale. The Weany Creek model has been able to show in detail which stream sections (or their associated watersheds) contribute most to suspended sediment loads, as well as where bedload deposits are most likely to accumulate. Additional detail regarding whether erosion is derived from hillslope, or combined gully/bank erosion, or both, has provided valuable insight into the sub-catchment-scale dynamics of erosion. The Weany Creek model has been also used to determine the impact of changes in management practice on sediment erosion, transport and accumulation. A scenario with reduced stocking rates was shown to reduce the delivery of sediment to stream, and consequently led to a lower delivery of fine sediment to downstream reaches.

Decrease in southeastern Australian water availability linked to ongoing Hadley cell expansion

Southeastern Australia experienced the worst drought of the instrumental record from 1997 to 2009, which was broken by Australias wettest 2 year period on record (2010/2011). This drought was primarily a cool season (April to October) phenomenon. In contrast, the breaking of the drought was a warm season (November to March) phenomenon. This reduction in winter rainfall along with an absence of very wet months led to a greater reduction in streamflow across the region than would be anticipated based on the 12% reduction in mean annual rainfall alone. The results presented in this article have linked the extent, duration, and severity of this drought to the ongoing observed expansion of the Southern Hemisphere Hadley cell at a rate of 0.5°/decade. This expansion has intensified the subtropical ridge over southern Australia, pushing cool season midlatitude storm tracks further south, leading to a reduction in winter rainfall and runoff across the region.

Integrative modelling of climatic, terrestrial and fluvial systems

The contributions included in this special issue of Environmental Modelling & Software have been selected from the papers presented at the 2003 Modelling and Simulation Congress (MODSIM 2003) held in Townsville, Australia. MODSIM 2003 was the 15th biannual gathering of the Modelling and Simulation Society of Australia and New Zealand (MSSANZ), an organisation with more than 500 members from 50 countries. The theme of the congress was “Integrative Modelling of Biophysical, Social and Economic Systems for Resource Management Solutions” and the emphasis of the majority of the congress papers was on integration, namely using modelling techniques to bring together the natural environment, social considerations and economic improvement or provide information which can be used for integrative decision making.

Preface to: The modelling of hydrologic systems

This special issue of Environmental Modelling and Software encapsulates papers that describe topical aspects of the modelling of hydrologic systems. Papers for the special issue were selected from the MODSIM 2001 Conference. The MODSIM 2001 Conference was organised by the Modelling and Simulation Society of Australia and New Zealand Inc. (http://mssanz.cres.anu.edu.au/ ). It was held at the Australian National University from 10–13 December 2001. We have selected 16 interesting papers presented at the conference to compile the issue. The papers span two major themes: (i) hydrologic modelling of flow in the first six papers; and (ii) the modelling of water quality and sediment transport in the remainder. These two themes reflect the sessions from which they were sourced. A wide variety of modelling techniques are described across the various papers of the special issue. The models have been applied in a similarly diverse range of environments: from the Mississippi River at St Louis, arid flood plains in Australia, to bench terraces in West Java. The first paper, by Tom Chapman, examines the modelling of stream recession flows. It challenges the common assumption that all recharge occurs during periods of surface runoff. Justin Costelloe, Roger Grayson, Robert Argent and Tom McMahon describe techniques for modelling the flow regime of an arid zone floodplain. They use a case study of the Diamantina River where a grid-based daily time-step conceptual model is used for flow routing. A paper by Barry Croke and Peter Dye is concerned with the application and evaluation of the IHACRES rainfall-runoff model for investigating effects of land use change in several South African catchments. David Post, Anne Kinsey-Henderson, Lachlan Stewart, Christian Roth and John Reghenzani report on the application of Mike-11—a one-dimensional flow routing model used in this instance for investigating drainage of inundated sugar cane fields in the Ripple Creek catchment. Bellie Sivakumar describes nonlinear prediction methods used for forecasting monthly streamflow dynamics in the western United States. Jenifer Ticehurst, Hamish Cresswell and Anthony Jakeman describe a sensitivity analysis of the two-dimensional HILLS hydrologic model. Lachlan Newham, John Norton, Ian Prosser and Anthony Jakeman also describe sensitivity analysis techniques. They investigate parameter sensitivities of the