Development of pan coefficients for estimating evapotranspiration from riparian woody vegetation

Abstract

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.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…phenology, LAI) and function (e.g. ET, gross primary productivity) has become increasingly sophisticated (Glenn et al, 2010;Yuan et al, 2010;Jung et al, 2011;Rossini et al, 2012;Kanniah et al, 2013;Ma et al, 2013;Nagler et al, 2013) and increasingly applied to realworld applications of water resources management (Scott et al, 2008;Glenn et al, 2010;Barron et al, 2014;Doody et al, 2014). Remote sensing (RS) provides a robust and spatially explicit means to assess not only vegetation structure and function but also relationships amongst these and climate variables.…”

“…Accurate and spatially distributed estimates of discharge through vegetation are difficult to obtain through field measurements. Recently, RS methods have been calibrated against Penman-Monteith estimates of ET (Glenn et al, 2010;Nagler et al, 2013;Doody et al, 2014), which requires only standard weather data (net radiation, wind speed and vapour pressure deficit) and thus increases the coverage of calibration sites. Because ET in GDEs is generally not limited by soil moisture when groundwater is of high quality (i.e.…”

Drip irrigation enhances shallow groundwater contribution to crop water consumption in an arid area

“…In Australia, soil salinization impacts the natural vegetation creating poor health and death in relation to changes of the surface water regime of the River Murray, which alters groundwater–surface water interactions (Doody, Holland, Benyon, & Jolly, ; Jolly, Walker, & Thorburn, ). Faced with reductions in stream water availability, introduced vegetation is often removed from within riparian areas in Australia and the United States, in order to return water to streams (Doody et al, ; Doody, Benyon, Theiveyanathan, Koul, & Stewart, ). Therefore, monitoring use of shallow groundwater and increasing water use efficiency are of significant importance for water resources and vegetation condition in arid and semi‐arid areas globally.…”

“…Reduced extraction from surface water and groundwater can also preserve native groundwater‐dependent vegetation. Therefore, in areas where groundwater promotes the growth of vegetation or natural plants, water use efficiencies will protect and preserve the environment by reducing irrigation losses (Doody et al, ; Mata‐González, McLendon, Martin, Trlica, & Pearce, ).…”

Generation of continuous surface soil moisture dataset using combined optical and thermal infrared images

“…Surface soil moisture (SSM) plays an important role in the flux of water and energy between the atmosphere and the Earth's surface. As a key state variable of the hydrological cycle, SSM controls most of the physical processes on Earth, including rainfall infiltration, terrestrial evapotranspiration, and other pivotal indirect ecosystem functions, such as photosynthesis and crop growth (Anderson, Udawatta, Seobi, & Garrett, ; Arora & Boer, ; Doody, Benyon, Theiveyanathan, Koul, & Stewart, ; Dobriyal, Qureshi, Badola, & Hussain, ; Engman, ; Holzman, Rivas, & Piccolo, ; Laiolo et al, ; Li et al, ; Schneider & Childers, ). SSM also governs the partitioning of surface available energy into sensible and latent heat flux through evaporation and transpiration processes (Cui & Wang, ; Petropoulos, Ireland, & Barrett, ).…”