Tim McVicar

As a partial conclusion, we do argue that indeed, using the T-M formula as the theoretical reference is a ‘strong’ assumption which explains that a bivariate solution to elasticity is better that a monovariate one. However, beyond reflecting the “hydrological good sense”, it also reflects the visual impression from the graphs that we present in supplement. Moreover, we believe that the T-M formula’s assumptions are likely to be shared by most hydrologists, and that the T-M formula is both extremely simple and widely-used, which should turn our demonstration acceptable to many of our readers. We thank AV for his suggestion to show graphically that the TM formula implies well defined elasticities at moderate aridity conditions, and we will use this graph in the revised version.

Forest plantations can access water from some unconfined aquifers that also contain nitrate at concentrations that could support hydroponic culture, but the separate effects of such additional water and nitrogen availability on tree growth have not hitherto been quantified. We demonstrate these effects using simulation modelling at two contrasting sites supporting Eucalyptus globulus Labill. or Pinus radiata D.Don plantations. The APSIM Eucalyptus and Pinus models simulated plantation growth within 2% of observed growth where the water table was at 4 m depth for eucalypts (height 28 m, MAI 32 m3 ha−1 year−1) and at 23 m for pines (height 37 m, MAI 20 m3 ha−1 year−1). In simulations without an aquifer, observed growth could only be matched using unrealistically high surface soil nitrogen (N) supply, suggesting this is an unlikely mechanism. Simulated aquifer N concentrations, evapotranspiration, and net N mineralization and leaching (emergent properties of modelling) were similar to ...

mission of the Cooperative Research Centre for Sustainable Rice Production and/or the individual parties to that joint venture (the " Parties "). Disclaimer The information in this publication is based on knowledge available at the time of writing. The publication is presented in good faith and has been made available by the Cooperative Research Centre for Sustainable Rice Production (Rice CRC) on the basis that recipients of the publication should make their own enquiries and obtain appropriate professional advice before relying on any information or any expression of opinion or prediction contained in this publication. Neither the joint venture known as the Cooperative Research Centre for Sustainable Rice Production (Rice CRC) nor its individual member parties accept liability for any losses, damages or costs resulting from the use of information contained in or omitted from this publication. The views expressed and the conclusions reached in this publication are those o...

The onus for monitoring crop growth from space is its ability to be applied anytime and anywhere, to produce crop yield estimates that are consistent at both the subfield scale for farming management strategies and the country level for national crop yield assessment. Historically, the requirements for satellites to successfully monitor crop growth and yield differed depending on the extent of the area being monitored. Diverging imaging capabilities can be reconciled by blending images from high-temporal-frequency (HTF) and high-spatial-resolution (HSR) sensors to produce images that possess both HTF and HSR characteristics across large areas. We evaluated the relative performance of Moderate Resolution Imaging Spectroradiometer (MODIS), Landsat, and blended imagery for crop yield estimates (2009–2015) using a carbon-turnover yield model deployed across the Australian cropping area. Based on the fraction of missing Landsat observations, we further developed a parsimonious framework ...

We present new global maps of the Köppen-Geiger climate classification at an unprecedented 1-km resolution for the present-day (1980-2016) and for projected future conditions (2071-2100) under climate change. The present-day map is derived from an ensemble of four high-resolution, topographically-corrected climatic maps. The future map is derived from an ensemble of 32 climate model projections (scenario RCP8.5), by superimposing the projected climate change anomaly on the baseline high-resolution climatic maps. For both time periods we calculate confidence levels from the ensemble spread, providing valuable indications of the reliability of the classifications. The new maps exhibit a higher classification accuracy and substantially more detail than previous maps, particularly in regions with sharp spatial or elevation gradients. We anticipate the new maps will be useful for numerous applications, including species and vegetation distribution modeling. The new maps including the ass...

Elevated atmospheric COconcentration (eC) might reduce forest water-use, due to decreased transpiration, following partial stomatal closure, thus enhancing water-use efficiency and productivity at low water availability. If evapotranspiration (E) is reduced, it may subsequently increase soil water storage (ΔS) or surface runoff (R) and drainage (D), although these could be offset or even reversed by changes in vegetation structure, mainly increased leaf area index (L). To understand the effect of eCin a water-limited ecosystem, we tested whether two years of eC(~40% increase) affected the hydrological partitioning in a mature water-limited Eucalyptus woodland exposed to Free-Air COEnrichment (FACE). This timeframe allowed us to evaluate whether physiological effects of eCreduced stand water-use irrespective of L, which was unaffected by eCin this timeframe. We hypothesized that eCwould reduce tree-canopy transpiration (E), but excess water from reduced Ewould be lost via increased s...

As the "Asian Water Tower", the Tibetan Plateau (TP) provides water resources for more than 1.4 billion people, but suffers from climatic and environmental changes, followed by the changes in water balance components. We used state-of-the-art satellite-based products to estimate spatial and temporal variations and trends in annual precipitation, evapotranspiration and total water storage change across eastern TP, which were then used to reconstruct an annual runoff variability series for 2003-2014. The basin-scale reconstructed streamflow variability matched well with gauge observations for five large rivers. Annual runoff increased strongly in dry part because of increases in precipitation, but decreased in wet part because of decreases in precipitation, aggravated by noticeable increases in evapotranspiration in the north of wet part. Although precipitation primarily governed temporal-spatial pattern of runoff, total water storage change contributed greatly to runoff var...

Using thermal remote sensing to monitor land degradation and salinization in the Murray-darling basin of Australia. David LB Jupp, Joe Walker, Jetse D Kalma, Tim McVicar ENVIRONMENTAL RESEARCH INST OF MICHIGAN, ANN ARBOR, MI,(USA). 2, 1011-1021, 1990. ...

Drought is an intermittent disturbance of the water cycle that profoundly affects the terrestrial carbon cycle. However, the response of the coupled water and carbon cycles to drought and the underlying mechanisms remain unclear. Here we provide the first global synthesis of the drought effect on ecosystem water use efficiency (WUE = gross primary production (GPP)/evapotranspiration (ET)). Using two observational WUE datasets (i.e., eddy-covariance measurements at 95 sites (526 site-years) and global gridded diagnostic modelling based on existing observation and a data-adaptive machine learning approach), we find a contrasting response of WUE to drought between arid (WUE increases with drought) and semi-arid/sub-humid ecosystems (WUE decreases with drought), which is attributed to different sensitivities of ecosystem processes to changes in hydro-climatic conditions. WUE variability in arid ecosystems is primarily controlled by physical processes (i.e., evaporation), whereas WUE var...

The classification of crops from remote sensing has become an important part of agricultural management, and as a result, has instigated a great deal of research aimed at increasing classification accuracy through various methods and techniques. However, comparatively little research has been performed on determining the best time(s) of image acquisition for crop discrimination even though this could impact classification

Satellite and on-ground observations over Australia were analysed and compared with output from land surface models to investigate changes in the interaction between atmosphere, water cycle and vegetation. Observations included top soil water content and vegetation vigour derived from passive microwave satellite observations since 1979, remotely sensed gravity anomalies (indicative of changes in soil water and groundwater storage) since 2002,

ABSTRACT Many environmental problems are caused by changes in aspects of the hydrological cycle. Water balance model-ling combined with field experiments can give us a better understanding of the components of the hydrological cycle from which to develop appropriate management options. Water balance models can be constructed at any level of complexity. In simple 'bucket' models only the most important processes are represented. When appro-priately used, bucket models can provide useful insights into the functional behaviour of a system. Complex models are needed to understand complex feedbacks and interactions among different processes of the system. However, increasing the complexity of a model does not necessarily lead to a more accurate model and it is essential that model complexity matches the availability of data. The key to successful water balance modelling is to have a clearly defined objective and to select an appropriate model. This chapter outlines the principles of water balance modelling and explains how models can be used in crop management.

The evolution of remote sensing and classification methods has enabled effective mapping, monitoring and management of irrigated agriculture. A random forest classification was implemented using learning samples inferred from Landsat TM/ETM data and monthly time-series of remotely-sensed observations from the MODerate resolution Imaging Spectroradiometer (MODIS). The covariates included in the method characterised: (i) the vegetation phenology via the recurrent and persistent fractions of photosynthetically active radiation (fPARrecandfPARper, respectively); (ii) vegetation water use via estimates of actual evapotranspiration (AET), rainfall (P) and the difference between AET and P . Maps of irrigated areas under different climates and cropping conditions were produced for the whole Murray-Darling Basin (Australia) for the years 2004 to 2010 with 0.96 observed agreement in terms of the Kappa Index (were a value of 1 indicates perfect agreement). An independent comparison of yearly irrigated area estimates and corresponding water use showed a linear relationship with good agreement (R2 >0.7) against available yearly metered water withdrawals and estimates of agricultural yields. A sequential covariate optimisation suggested that the most important predictors included the emergence-senescence period (as determined by the fPARrec and corresponding rates of change) and the AET surplus over P during this period. The latter can be important when determining more opportunistic irrigation practices due to unreliable water supply in areas with otherwise high annual rainfall. The procedure can be implemented to map irrigated areas at the global scale: the MODIS time-series used in the classification methodology are available globally since February 2000 and so are the Landsat archives which can be used to infer learning samples and irrigation practices elsewhere.

Evapotranspiration (ET) is the process by which liquid water becomes water vapor and energetically this accounts for much of incoming solar radiation. If this ET did not occur temperatures would be higher, so understanding ET trends is crucial to predict future temperatures. Recent studies have reported prolonged declines in ET in recent decades, although these declines may relate to climate variability. Here, we used a well-validated diagnostic model to estimate daily ET during 1981-2012, and its three components: transpiration from vegetation (Et), direct evaporation from the soil (Es) and vaporization of intercepted rainfall from vegetation (Ei). During this period, ET over land has increased significantly (p < 0.01), caused by increases in Et and Ei, which are partially counteracted by Es decreasing. These contrasting trends are primarily driven by increases in vegetation leaf area index, dominated by greening. The overall increase in Et over land is about twofold of the decr...

Globally, irrigation accounts for more than two thirds of freshwater demand. Recent regional and global assessments indicate that groundwater extraction (GWE) for irrigation has increased more rapidly than surface water extraction (SWE), potentially resulting in groundwater depletion. Irrigated agriculture in semi-arid and arid regions is usually from a combination of stored surface water and groundwater. This paper assesses the usefulness of remotely-sensed (RS) derived information on both irrigation dynamics and rates of actual evapotranspiration which are both input to a river-reach water balance model in order to quantify irrigation water use and water provenance (either surface water or groundwater). The assessment is implemented for the water-years 2004/05-2010/11 in five reaches of the Murray-Darling Basin (Australia); a heavily regulated basin with large irrigated areas and periodic droughts and floods. Irrigated area and water use are identified each water-year (from July to June) through a Random Forest model which uses RS vegetation phenology and actual evapotranspiration as predicting variables. Both irrigated areas and actual evapotranspiration from irrigated areas were compared against published estimates of irrigated areas and total water extraction (SWE+GWE).The river-reach model determines the irrigated area that can be serviced with stored surface water (SWE), and the remainder area (as determined by the Random Forest Model) is assumed to be supplemented by groundwater (GWE). Model results were evaluated against observed SWE and GWE. The modelled SWE generally captures the observed interannual patterns and to some extent the magnitudes, with Pearson's correlation coefficients >0.8 and normalised root-mean-square-error<30%. In terms of magnitude, the results were as accurate as or better than those of more traditional (i.e., using areas that fluctuate based on water resource availability and prescribed crop factors) irrigation modelling. The RS irrigated areas and actual evapotranspiration can be used to: (i) understand irrigation dynamics, (ii) constrain irrigation models in data scarce regions, as well as (iii) pinpointing areas that require better ground-based monitoring.