Thomas Mcmahon

• B E, Dip Ed, PhD, D Eng
• Professor Emeritus at University of Melbourne

There is an extensive literature dealing with the interaction between groundwater and surface water, and this includes major reviews on baseflow, transmission losses, baseflow recession analysis, and broader aspects of low flows. Although these are mature topics in hydrology, they continue to attract strong interest, with hundreds of papers publish...

Rainfall‐runoff models are used across academia and industry, and the number and type have proliferated over time. In this primer we briefly introduce the key features of these models and provide an overview of their historical development and drivers behind those developments. To complete the discussion there is a brief section on model choice inc...

There has been a resurgence of interest in the construction of large dams worldwide. This study examined many dams from around the world (>10,000) and compared them to a comprehensive dataset developed for Australia (224) to provide insights that might otherwise not be apparent from examining just one or several dams. The dam datasets (ICOLD and AN...

In the discussion of Eq. (1), reference is made to an example calculation of the metric that should have been provided in the right-hand panel of Fig. 1.

Hydrologists are commonly involved in impact, adaption and vulnerability assessments for climate change projections. This paper presents a framework for how such assessments can better differentiate between the impacts of climate change and those of natural variability, an important differentiation as it relates to the vulnerability to water availa...

The purpose of this paper is to determine uncertainty in the gauged range of the stage-gauged discharge relationship for 622 rating curves from 171 Australian Bureau of Meteorology Hydrologic Reference stream gauging Stations (HRS). Water agencies use many methods to establish rating curves. Here we adopt a consistent method across all stations and...

Major restructuring including commercialisation of the water authorities in Australia during the past several decades has resulted in the loss of much valuable information on dam infrastructure costs. This paper sets out to provide an Australian perspective on dam costs and dam cost overruns, examine patterns of dam costs and cost overruns, and dev...

This paper discusses the use of methods commonly used by engineering hydrologists in undertaking surface water investigations. While the conceptual basis of the approaches covered is rooted in best international practice, the discussion focuses on data and procedures directly applicable to Australian conditions. The impetus for this paper arises fr...

Evaporation plays a key role in the hydrology of a catchment. World‐wide actual terrestrial evaporation is approximately two third of terrestrial precipitation. Evaporation is the focus of this study in which we describe the historical developments of models for estimating evaporation from standard meteorological data. Although Aristotle and Descar...

Two key sources of uncertainty in projections of future runoff for climate change impact assessments are uncertainty between global climate models (GCMs) and within a GCM. Within-GCM uncertainty is the variability in GCM output that occurs when running a scenario multiple times but each run has slightly different, but equally plausible, initial con...

The objective of this paper is to identify better performing Coupled Model Intercomparison Project phase 3 (CMIP3) global climate models (GCMs) that reproduce grid-scale climatological statistics of observed precipitation and temperature for input to hydrologic simulation over global land regions. Current assessments are aimed mainly at examining t...

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This paper quantifies long-run hydrological persistence in reservoir inflows to two regions: Melbourne and Sydney. We use a relatively new approach in hydrology, Empirical Mode Decomposition (EMD). Our three key results are summarised below: (1) For Melbourne and Sydney inflows, 57-66% of total variance was accounted for by periodicities <10 years;...

Two key sources of uncertainty in projections of future runoff for climate change impact assessments are uncertainty between Global Climate Models (GCMs) and within a GCM. Within-GCM uncertainty is the variability in GCM output that occurs when running a scenario multiple times but each run has slightly different, but equally plausible, initial con...

Two key sources of uncertainty in projections of future runoff for climate change impact assessments are uncertainty between Global Climate Models (GCMs) and within a GCM. Uncertainty between GCM projections of future climate can be assessed through analysis of runs of a given scenario from a wide range of GCMs. Within GCM uncertainty is the variab...

Estimating evaporation from standard meteorological data continues to be an active area of research and practical application. Here we report on recent progress in using standard meteorology data to estimate potential, reference and actual evaporation from terrestrial landscapes as well as evaporation from lakes and reservoirs. We also address rece...

In the paper by McMahon et al. (2013, supplementary sections S8 and S19, worked example 8), the Szilagyi-Jozsa advection-aridity model (Szilagyi, 2007; Szilagyi and Jozsa, 2008) was not applied in the worked example as intended by author J. Szilagyi. This commentary seeks to clarify the issue and provide the correct procedure.

In the paper by McMahon et al. (2013, Supplement Sects. S8 and S19 (Worked Example 8)), the Szilagyi-Jozsa Advection-Aridity model (Szilagyi, 2007; Szilagyi and Jozsa, 2008), which is a modification of the original Advection Aridity model of Brutsaert and Strickler (1979), was not applied in the worked example as intended by author J. Szilagyi. Thi...

This guide to estimating daily and monthly actual, potential, reference crop and pan evaporation covers topics that are of interest to researchers, consulting hydrologists and practicing engineers. Topics include estimating actual evaporation from deep lakes and from farm dams and for catchment water balance studies, estimating potential evaporatio...

The effect of forest cover changes on mean streamflow is well understood and worldwide data have shown that increasing forest cover decreases the total volume of flow at the catchment scale. However, due to the different methods used to assess the impact of forest cover at the annual and sub-annual timescale general conclusions can be difficult to...

This guide to estimating daily and monthly actual, potential, reference crop and pan evaporation covers topics that are of interest to researchers, consulting hydrologists and practicing engineers. Topics include estimating actual evaporation from deep lakes and from farm dams and for catchment water balance studies, estimating potential evaporatio...

Finkl and Cathcart have proposed a macroengineering project to deliver water from the Fly River in Papua New Guinea via an undersea pipeline into northeast Australia, routed down the Diamantina River and thence into Lake Eyre. The proposal has historical antecedents but its scientific basis is very weak. No case is made for the usefulness or demand...

In this chapter we set out to discuss surface hydrology at the global scale and in doing so we will place emphasis on surface runoff, both direct and as baseflow, since this is the harvestable part of the hydrologic cycle. Of all the freshwater on Earth, only about 0.3% is surface water while the rest is frozen in the ice caps and glaciers or in th...

Overlying the challenge of managing within natural hydroclimatic variability is the likely modification of runoff variability along with average runoff due to anthropogenic enhancement of greenhouse gas concentrations. In this paper analytical models are developed in which runoff mean and variability, the latter defined by the variance (or standard...

Research into the role of catchment vegetation within the hydrologic cycle has a long history in the hydrologic literature. Relationships between vegetation type and catchment evapotranspiration and runoff were primarily assessed through paired catchment studies during the 20th century. Results from over 200 paired catchment studies from around the...

Historically, relationships between catchment vegetation type, evapotranspiration and runoff have been assessed primarily through paired catchment studies. The literature contains results from over 200 of these studies from around the world but two factors limit the applicability of the results to the wider domain. Firstly, catchment areas are gene...

Debate about irrigation development of water resources in northern Australia has been hampered by a lack of quantitative information to enable accurate assessment of the volume of water that could potentially be regulated in the ‘North’ (north of the tropic of Capricorn). Too often the debate focuses solely on streamflow volumes and quantities of r...

Climate, described here using the Köppen–Geiger classification, plays a dominant role in determining the total flow, interannual variability, seasonal regime, extremes of high and low flow of rivers, and the nature of river channels. Mean annual runoff is the product of the climatic water balance which in arid areas is dominated by losses to evapot...

There is much in the scientific literature dealing with methods to determine environmental water requirements in streams. However, most of these methods are suited to long-term water resource planning and setting regulatory targets. In Australia, the environment is now recognized as a legitimate user of water with its own water entitlement. With th...

Empirical mode decomposition (EMD), an adaptive data analysis methodology, has the attractive feature of robustness in th presence of nonlinear and non-stationary time series. Recently, in this journal, Pegram and co-authors (Pegram et al. 2008 Proc. R. Soc. A 464, 1483–1501), proposed a modification to the EMD algorithm whereby rational splines re...

This paper introduces a new approach to stochastically generating rainfall sequences that can take into account natural climate phenomena, such as the El Niño-Southern Oscillation and the interdecadal Pacific oscillation. The approach is also amenable to modeling projected affects of anthropogenic climate change. The method uses a relatively new te...

This is the second of two papers examining the surface hydrology of the Lake Eyre Basin (LEB) (1,140,000 km2) in Australia. The streams are unregulated and are characterised by extreme discharge variation. The analyses reported cover only surface hydrology and include comparisons with arid zone catchments globally. The paper discusses spatial runof...

This is the first of two papers that describe the surface hydrology of the Lake Eyre Basin (LEB) (1,140,000km2) in central Australia and compares some key characteristics with those observed from arid regions globally. This paper concentrates on annual rainfall, whereas the second paper is devoted to streamflow. The first part describes the LEB's c...

Annual, monthly and daily streamflows from 99 unregulated rivers across northern Australia were analysed to assess the general surface water resources of the region and their implications for development. The potential for carry-over storages was assessed using the Gould-Dincer Gamma method, which utilises the mean, standard deviation, skewness and...

Changed land use and irrigation has increased recharge to the groundwater system in irrigated areas worldwide. This altered hydraulic regime increases salt discharge by either mobilising stored salt or increasing salt loading from irrigation application. The salt is transported to surface drainage and river systems through the following processes;...

Empirical mode decomposition (EMD), a relatively new form of time-series decomposition, has the feature of not assuming tha a time series is linear or stationary, as is implicitly done in Fourier analysis. In natural time series such as records o rainfall, streamflow, temperature, etc., where most variables exhibit nonlinear and non-stationary beha...

This technical note describes the data and analysis to determine a factor to adjust theoretical estimates of reservoir storage capacity, based only on annual inflow hydrology, for practical issues including net evaporation loss, varying operating rules and seasonal demands, monthly inflow variability, dead storage, and site characteristics. Based o...

Environmental flows in unregulated rivers require a different management approach to regulated systems, where reservoirs allow more adaptive management of flows and water markets are well established. Governments in Australia have been investigating tender approaches to buy back water in unregulated systems. A. number of organisations in the Columb...

This is the final paper in a series of three dealing with global hydrology based on a world-wide historical data set of monthly and annual streamflow records. In this paper hypothetical reservoir capacity estimates and reservoir-yield performance characteristics are compared between countries and between climate zones. The comparison for each chara...

This is the first of three related papers that summarizes streamflow character-istics of a set of 1221 global rivers. The rivers are well distributed world-wide, are un-impacted by upstream reservoirs or diversions for the period of data collection and have at least 10 years of continuous monthly and annual streamflow data. The following key featur...

This is the second of three papers describing hydrologic analyses of monthly and annual streamflow data for a global set of 729 unregulated rivers with at least 25 years of continuous data. Capacity estimates of hypothetical reservoirs are computed for each river using the Sequent Peak Algorithm (SPA), Behaviour analysis and the Gould Dincer Gamma...

Although now over 100 years old, the classification of climate originally formulated by Wladimir Köppen and modified by his collaborators and successors, is still in widespread use. It is widely used in teaching school and undergraduate courses on climate. It is also still in regular use by researchers across a range of disciplines as a basis for c...

Understanding the retention time of water in waterbodies during periods of no surface flow in dryland rivers provides an important context for evaluating the ecological importance of a waterhole to the river system. Time series of water level data were collected from 10 waterbodies spread across three river systems of the Lake Eyre Basin (LBE), Aus...

The Gould–Dincer suite of techniques (normal, log-normal and Gamma), which is used to estimate the reservoir capacity–yield–reliability (S–Y–R) relationship, is the only known available procedure in the form of a simple formula, based on annual streamflow statistics, that allows one to compute the S–Y–R relationship for a single storage capacity ac...

Annual and monthly streamflows for 729 rivers from a global data set are used to assess the adequacy of five techniques to estimate the relationship between reservoir capacity, target draft (or yield) and reliability of supply. The techniques examined are extended deficit analysis (EDA), behaviour analysis, sequent peak algorithm (SPA), Vogel and S...

The long-term sustainability of irrigated agriculture depends on protecting land and water resources from salinity. Generally, a favourable salt balance (mass out ≥ mass in) is considered necessary for sustainable irrigated agriculture. This concept has been used in irrigated agricultural systems to satisfy varying objectives. In this paper we disc...

Estimates of the upper constraint on actual evapotranspiration are required as input data in the majority of rainfall‐runoff models. This paper compares and discusses the applicability of Penman's potential evapotranspiration estimates and Morton's wet environment evapotranspiration estimates in rainfall‐runoff modeling applications. Morton's wet e...

This study introduces a method based on LH moments to use the generalized extreme value (GEV) distribution for low-flow frequency analysis and investigates the capability of the GEV distribution fitted by LH moments to effectively model the lower tail of the low-flow frequency curve, without explicitly censoring the data sample. The performance of...

EXTENDED ABSTRACT Empirical mode decomposition (EMD), a relatively new form of time series decomposition, has the feature of not assuming a time series is linear or stationary (like Fourier analysis). In hydroclimatology, where most variables exhibit non-linear and non-stationary behaviour, this feature is particularly useful, allowing more meaning...

Gedney et al. attribute an increase in the twentieth-century continental runoff to the suppression of plant transpiration by CO2-induced stomatal closure, by replicating a continental runoff data set. However, we have concerns about this data set and the methods used to construct it, in addition to those already raised, which we believe may undermi...

The potential impact of climate change on the variability structure of climate has been investigated predominately through changes to extreme event frequency or the shape of the daily frequency distribution. Recent change to interannual climate variability has received less attention. Here we report that the interannual variability of temperature a...

The Comet River in Central Queensland, Australia, with a catchment area of 16,440 km2 was largely cleared of a natural forest cover dominated mainly by Brigalow (Acacia harpophylla) during the mid-1960s. This provides an opportunity to examine the scale dependence of the impact on runoff from a large catchment of the conversion of forest to grass a...

Considerable attention has been paid to the downstream effects of reservoirs on the ecology of rivers, streams and wetlands. However, most reservoirs were constructed well before ecological concerns became prominent. Little attention has been given to the question of what extent existing structures and management systems can accommodate changes. Th...

This paper examines 10 reservoir performance metrics including time and volume based reliability, several measures of resilience and vulnerability, drought risk index and sustainability. Both historical and stochastically generated streamflows are considered as inflows to a range of hypothetical storage on four rivers—Earn river in the United Kingd...

Anastomosing rivers form a subset of the anabranching family of river types and provide considerable challenges to modelling of their streamflow because of complex flow patterns across greatly varying floodplain widths. Estimates of distributed flow data are required for catchment management purposes and ecological studies of these rivers but are h...

Monthly rainfall data are needed in the simulation of water resources systems, and in the estimation of water yield from large catchments. Models to generate monthly streamflow data can be applied to generate monthly rainfall data, but this presents problems for most regions, which have significant months of no rainfall. This paper compares two est...

A hay drying model (HAYDMO) which predicts the moisture content of pasture hay is described. It uses multiple regression equations based on field drying experiments with conditioned and unconditioned hay and predicts hourly changes in moisture content for both day and night and also those due to rain. The model can be used with three different comb...

Water markets have great potential to increase the efficiency of water use. However, the very process of transferring a water entitlement can result in third party effects. Specifically, there are three types of impact that can affect the entitlements of third party irrigators: volumetric reliability, delivery reliability and water quality effects....

Water markets have great potential to increase the efficiency of water use. However, the very process of transferring a water entitlement can result in third party effects. Specifically, there are three types of impact that can affect the entitlements of third party irrigators: volumetric reliability, delivery reliability and water quality effects....

Estimates of the sensitivity of streamflow to climate are required to make informed decisions for managing water resources and environmental systems to cope with hydroclimatic variability and climate change. The precipitation elasticity of streamflow (εp), defined as the proportional change in mean annual streamflow divided by the proportional chan...

This study describes the spatial and temporal variability of water salinity of the Neales–Peake, an ephemeral river system in the arid Lake Eyre basin of central Australia. Saline to hypersaline waterholes occur in the lower reaches of the Neales–Peake catchment and lie downstream of subcatchments containing artesian mound springs. Flood pulses are...

Paired catchment studies have been widely used as a means of determining the magnitude of water yield changes resulting from changes in vegetation. This review focuses on the use of paired catchment studies for determining the changes in water yield at various time scales resulting from permanent changes in vegetation. The review considers long ter...

There has been extensive research on the problem of stochastically generating daily rainfall sequences for use in water management applications. Srikanthan and McMahon [Australia Water Resources Council, Canberra, 1985] proposed a transition probability matrix (TPM) model that performs better for Australian rainfall than many alternative models, pa...

Water trading in Australia is enabled by much historical institutional development, which had other objectives at the time that it was implemented. After 2 decades of institutional reform to enable water markets in the Murray Darling Basin, active markets are reallocating surface water entitlements among irrigation users. However, permanent water t...

An important factor controlling catchment-scale water balance is the seasonal variation of climate. The aim of this study is to investigate the effect of the seasonal distributions of water and energy, and their interactions with the soil moisture store, on mean annual water balance in Australia at catchment scales using a stochastic model of soil...

Australian arid zone ephemeral rivers are typically unregulated and maintain a high level of biodiversity and ecological health. Understanding the ecosystem functions of these rivers requires an understanding of their hydrology. These rivers are typified by highly variable hydrological regimes and a paucity, often a complete absence, of hydrologica...

Fluctuations of wet and dry years have long been investigated in the climatology and hydrology literature. In this, the second of two papers investigating runs of consecutive dry years, the magnitude, also known as the intensity, and severity (length × magnitude) of dry runs are investigated. In the first paper the length of dry runs was investigat...

We thank Tromp van Meerveld and McDonnell (this issue) for their comment on our paper. They raise important issues about catchment response and the role of soil moisture. It is clearly important to reconcile different sources of field evidence. Tromp van Meerveld and McDonnell argue that at the Panola research hillslope, transient subsurface satura...

The Cooperative Research Centre for Catchment Hydrology (CRCCH) has embarked on a research project under the Climate Variability Program to build a tool kit that will include stochastic models to generate rainfall data. Stochastic models for generating rainfall data are usually evaluated subjectively by comparing a number of parameters estimated fr...

Water markets have the potential to greatly improve the productive use of water by reallocating entitlements to where they are most highly valued. However, trading can actually reduce the volumetric reliability of other parties' entitlements if relatively more water needs to be supplied to the transferred entitlement after the trade. Exchange rates...

Continental differences in the variability of annual runoff were reassessed using an expanded precipitation database and an improved methodology for allocating precipitation and runoff stations to Köppen climate zones. Application of the new Köppen zone allocation methodology resulted in changes in Köppen zone for 44% of runoff stations. Statistica...

The investigation of fluctuations of wet and dry years has a long history in the climatology and hydrology literature. In this, the first of two papers investigating runs of consecutive dry years, the lengths (persistence) of dry runs are investigated. In the second paper the magnitude/intensity and severity (length × magnitude) of dry runs will be...

The study of tree rings has been used for over 100 years to inform climatic and geomorphological reconstructions. In mainland Australia, no tree species are currently recognised as providing reliable sources for such studies over extensive areas. Eucalyptus camaldulensis is a widely growing species with a growth pattern that is closely linked to hi...

The geostatistical properties of soil moisture patterns from five different sites in Australia (Tarrawarra and Point Nepean) and New Zealand (three sites from the Mahurangi River Basin—Carran's, Clayden's and Satellite Station) are analysed here. The soil moisture data were collected using time domain reflectometry and consistent methods for all si...

A daily model was used to quantify the components of the total urban water balance of the Curtin catchment, Canberra, Australia. For this catchment, the mean annual rainfall was found to be three times greater than imported potable water, and the sum of the output from the separate stormwater and wastewater systems exceeded the input of imported po...

While the impact of vegetation on the mean annual water balance is well understood, there is a need to be able to predict the impact of vegetation changes on the magnitude and frequency of daily flows. A flow duration curve (FDC) displays the relationship between any given flow and the percentage of time that flow is exceeded. This paper provides a...

Arid zone, ephemeral rivers are characterised by discharge decreasing downstream in the lower reaches due to transmission losses. Modelling the flow regime of these rivers requires data on the spatial and temporal distribution of transmission losses in these reaches. In this study, a hydrological model is developed for a 330 km reach of the Diamant...

Streamflow data from 12 international rivers were used to develop predictive relationships for total (i.e. within-year plus over-year) reservoir capacity as well as the within-year capacity adjustment for use during reservoir planning. The models were then validated using data from three other international rivers. In general, it was found that the...

1. Droughts are not easily defined other than by culturally driven judgements about the extent and nature of impact. Natural ecosystems are adapted to the magnitude and frequency of dry periods and these are instrumental in controlling the long term functioning of these systems. 2. In unregulated rivers, low flows are derived from water in long-ter...

Ground-based measurement of the spatial distribution of soil moisture can be difficult because sampling is essentially made at a point and the choice of both sample depth and sample spacing affects the interpretation of the measurements.Hydrological interest has generally been in soil moisture of the root zone. Microwave Remote Sensing methods are...

Catchment-scale water balance is controlled by the seasonal variation of climate and catchment characteristics. The aim of this study is to investigate the suitability of a stochastic model of soil water balance with seasonally varying parameters, to predict mean-annual evapotranspiration at catchment scales. The rainfall regime at 262 catchments a...

The interannual variability in streamflow presents challenges in managing the associated risks and opportunities of water resources systems. This paper investigates the use of seasonal streamflow forecasts to help manage three water resources systems in south-east Australia. The seasonal streamflow forecasts are derived from the serial correlation...

El Niño/Southern Oscillation (ENSO) has been linked to climate anomalies throughout the world. This paper presents an overview of the relationship between ENSO and Australian rainfall and streamflow using data from 284 catchments throughout Australia. The ENSO-rainfall and ENSO-streamflow teleconnections are investigated by fitting a first harmonic...

The rationale for developing water markets is straightforward: to allocate water to the use where it will be valued most highly. However, designing and implementing a market for water entitlements that is efficient, equitable and sustainable, is very difficult. A simple system allowing people to buy and sell entitlements with no outside interventio...

The impact of changing catchment vegetation type on mean annual runoff has been known for some time, however, the impact on the variability of annual runoff has been established only recently. Differences in annual actual evapotranspiration between vegetation types and the potential effect of changing vegetation type on mean annual runoff and the v...

Over the past two decades there have been repeated calls for the collection of new data for use in developing hydrological science. The last few years have begun to bear fruit from the seeds sown by these calls, through increases in the availability and utility of remote sensing data, as well as the execution of campaigns in research catchments aim...

El Nino Southern Oscillation (ENSO) has been linked to climate anomalies throughout the world. This paper presents an overview of global ENSO-streamflow teleconnection and identifies regions where the relationship may be exploited to fore­ cast streamflow several months ahead. The teleconnection is investigated by fitting a first harmonic to 24-mon...

This paper presents the likely impacts of climate change on runoff, evapotranspiration and soil moisture in the more populated and important agricultural regions of Australia. The impacts are estimated by comparing the water fluxes simulated by a hydrologic model using present climate data and greenhouse-enhanced climate scenarios predicted by gene...