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Quantifying water use of various water consumers is an essential part of sustainable water management. Annual evapotranspiration (ET) of plantation forests often exceeds that of dryland agriculture, which in South Africa and South Australia has resulted in restrictions on plantation development. In the latter case, water licences are issued to commercial forestry plantations to account for higher ET compared to dryland pasture. Unlike irrigated crops, it is not practicable to measure water use of plantations directly and so in South Australia a set of 'deemed' average water use rates has been applied since 2013, based on species and depth to groundwater. Since South Australia's 'deemed' rates were calculated, additional plot‐scale measurements of annual ET from plantations <2 years old and post‐canopy closure have been used to quantify various components of ET. This has enabled development of two empirical ET models for plantations in South Australia's Lower Limestone Coast, and facilitated an advanced understanding of the effect of plantations on hydrological processes, particularly in relation to groundwater use. In this study, we applied these models to estimate rotation‐averaged annual ET and net groundwater impacts (net groundwater extraction plus recharge reduction compared to pasture) of plantations, driven by climate and groundwater depth, for comparison with the deemed rates. The modelling suggests that the groundwater impacts of plantations vary in space and time and that the deemed rates over‐estimate these impacts, on average. Accounting for variation in the effects of climate on the various components of ET, both spatially and temporally, may allow for more flexible rules for water resource allocation than using any simple, rule‐of‐thumb approach. [ABSTRACT FROM AUTHOR]

Transpiration (T) represents plant water use, while sun-induced chlorophyll fluorescence (SIF) emitted during photosynthesis, relates well to gross primary production. SIF can be influenced by vegetation structure, while uncertainties remain on how this might impact the relationship between SIF and T, especially for open and sparse woodlands. In this study, a method was developed to map T in riverine floodplain open woodland environments using satellite data coupled with a radiative transfer model (RTM). Specifically, we used FluorFLiES, a three-dimensional SIF RTM, to simulate the full spectrum of SIF for three open woodland sites with varying fractional vegetation cover. Five specific SIF bands were selected to quantify their correlation with field measured T derived from sap flow sensors. The coefficient of determination of the simulated far-red SIF and field measured T at a monthly scale was 0.93. However, when comparing red SIF from leaf scale to canopy scale to predict T, performance declined by 24%. In addition, varying soil reflectance and understory leaf area index had little effect on the correlation between SIF and T. The method developed can be applied regionally to predict tree water use using remotely sensed SIF datasets in areas of low data availability or accessibility. [ABSTRACT FROM AUTHOR]

Floodplain red gum forests ( Eucalyptus camaldulensis plus associated grasses, reeds and sedges) are sites of high biodiversity in otherwise arid regions of southeastern Australia. They depend on periodic floods from rivers, but dams and diversions have reduced flood frequencies and volumes, leading to deterioration of trees and associated biota. There is a need to determine their water requirements so environmental flows can be administered to maintain or restore the forests. Their water requirements include the frequency and extent of overbank flooding, which recharges the floodplain soils with water, as well as the actual amount of water consumed in evapotranspiration (ET). We estimated the flooding requirements and ET for a 38 134 ha area of red gum forest fed by the Murrumbidgee River in Yanga National Park, New South Wales. ET was estimated by three methods: sap flux sensors placed in individual trees; a remote sensing method based on the Enhanced Vegetation Index from MODIS satellite imagery and a water balance method based on differences between river flows into and out of the forest. The methods gave comparable estimates yet covered different spatial and temporal scales. We estimated flood frequency and volume requirements by comparing Normalized Difference Vegetation Index values from Landsat images with flood history from 1995 to 2014, which included both wet periods and dry periods. ET during wet years is about 50% of potential ET but is much less in dry years because of the trees' ability to control stomatal conductance. Based on our analyses plus other studies, red gum trees at this location require environmental flows of 2000 GL yr−1 every other year, with peak flows of 20 000 ML d−1, to produce flooding sufficient to keep them in good condition. However, only about 120-200 GL yr−1 of river water is consumed in ET, with the remainder flowing out of the forest where it enters the Murray River system. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrological processes within riparian environments worldwide are impacted when introduced species invade. Monitoring and management at substantial expense, are subsequently required to combat deleterious effects on the environment and stream hydrology. Willow species (Salicaceae: Salix spp.) introduced into Australia have spread throughout many riparian systems causing adverse environmental impacts, with high rates of water extraction when located within stream beds (in-stream willows) thus altering hydrology. Strategies exist to manage willows; however, simpler, more cost-effective methods are required to map and monitor spatial and temporal distributions. A method is presented to discriminate willow stands from surrounding native riparian vegetation using a single, very high 2 m resolution multispectral WorldView-2 satellite image. A combination of spectral bands 'coastal blue' (400-450 nm), 'red' (630-690 nm), 'red edge' (705-745 nm) and 'near infrared2' (860-1040 nm), minimum noise fraction transformation, median filtering and maximum likelihood supervised classification provided the highest discriminatory power within a 25 km2 study area. Of the spectral bands, coastal blue, red edge and near infrared2 are new bands that are not available in other multispectral sensors. These bands proved critical to the success of discriminating willows from other land cover categories (overall accuracy of 97%). Stream channels were defined by incorporating a LiDAR-derived digital elevation model to discriminate between willows on stream banks and within stream beds. Canopy area estimates of in-stream willows, coupled with water savings estimates from willow removal, suggest removal of 10.4 ha of Salix fragilis canopy from within river channels in the study area will potentially return 41 ML year−1 to the environment. The method presented improves our understanding of willow impacts on hydrology and aids decisions regarding willow removal for water resource management. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The long-term 'Millennium Drought' has put significant pressure on water resources across Australia. In southeastern Australia and in particular the Murray-Darling Basin, removal of exotic, high-water-use Salix trees may provide a means to return water to the environment. This paper describes a simple model to estimate evapotranspiration of two introduced Salix species under non-water-limited conditions across seven biogeoclimatic zones in Australia. In this study, Salix evapotranspiration was calculated using the Penman-Monteith model. Field measurements of leaf area index and stomatal conductance for Salix babylonica and Salix fragilis were used to parameterize the models. Each model was validated using extensive field estimates of evapotranspiration from a semi-arid ( S. babylonica, r2 = 0.88) and cool temperate ( S. fragilis, r2 = 0.99) region. Modelled mean annual evapotranspiration showed strong agreement with field measurements, being within 32 and 2 mm year−1 for S. babylonica and S. fragilis, respectively. Monthly pan coefficients (the ratio of mean evapotranspiration to mean pan evaporation) were developed from 30 years of meteorological data, for 30 key reference sites across Australia for both species using the validated Penman-Monteith models. Open-water evaporation was estimated from field measurements and was used to develop a simple linear regression model for open-water evaporation across the 30 reference sites. Differences between modelled evapotranspiration and open-water evaporation at each site provide an indication of the amount of water that might be returned to the environment from removal of in-stream Salix species. The monthly pan coefficient method reported has application across riparian environments worldwide where measured evapotranspiration is available for model validation. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The flow of precipitation from the surface through to groundwater in karst systems is a complex process involving storage in the unsaturated zone and diffuse and preferential recharge pathways. The processes associated with this behaviour are not well understood, despite the prevalence of karst aquifers being used as freshwater supplies. As a result, uncertainty regarding the ecohydrological processes in this geological setting remains large. In response to the need to better understand the impact of woody vegetation on groundwater recharge, annual evapotranspiration ( ET) rates and tree water sources were measured for two years above a shallow, fresh karst aquifer. Water use strategies of the co-occurring Eucalyptus diversifolia subsp. diversifolia Bonpl. and Allocasuarina verticillata (Lam.) L. Johnson were investigated using a monthly water balance approach, in conjunction with measurement of the stable isotopes of water, leaf water potentials and soil matric potentials. The results suggest that it is unlikely groundwater resources are required to sustain tree transpiration, despite its shallow proximity to the soil surface, and that similarities exist between ET losses and the estimated long-term average rainfall for this area. Irrespective of stand and morphological differences, E. diversifolia and A. verticillata ET rates showed remarkable convergence, demonstrating the ability of these co-occurring species to maximise their use of the available precipitation, which avoids the requirement to differentiate between these species when estimating ET at a landscape scale. We conclude that the water holding capacity of porous geological substrates, such as those associated with karst systems, will play an important role in equilibrating annual rainfall variability and should be considered when assessing ecohydrological links associated with karst systems. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]