Downscaling and Testing of Remote-Sensing Derived Evapo-Transpiration Products in Agricultural Landscapes

Evapo-transpiration (ET) presents a key component of managing water, not only for resources at the catchment scale, but also within agricultural landscapes. As almost two thirds of precipitation over land originates as ET, knowledge of ET provides insight into both rainfall patterns and plant water use, which in turn can inform land managers on biomass production and potential yields. Whilst there is an increasing array of spatial products available globally for use in monitoring ET (MODIS at 500m, METRIC at 30m etc.) they provide a suite of issues for fine resolution agricultural management. These problems include limited consideration of changes in land cover, which happens frequently within cropping scenarios due to rotations, and the validation of the products relies on stationary comparison sites at flux towers, many of which are located within natural landscapes, which are not representative of agricultural conditions. In this work we focus on MODIS ET and present a method for downscaling, incorporating both crop and soil information that can provide estimates of ET useful for within field management. We evaluate the ET product using multiple lines of evidence, including temporally using capacitance soil moisture probes, and spatially through crop yield monitor data and METRIC ET Values calculated from Landsat. We test the approach using a case study in south-eastern Australia, the Muttama creek catchment, a 1025 km2 sub catchment within the Murray-Darling basin in eastern Australia with approximately 620 mm of annual rainfall and predominately dryland cropping and grazing land use.