Evapotranspiration model comparison and an estimate of field scale Miscanthus canopy precipitation interception

The bioenergy crop Miscanthus x giganteus has a high water demand to quickly increase biomass with rapid canopy closure and effective rainfall interception, traits that are likely to impact on hydrology in land use change. Evapotranspiration (ET, the combination of plant and ground surface transpiration and evaporation) forms an important part of the water balance, and few ET models have been tested with Miscanthus. Therefore, this study uses field measurements to determine the most accurate ET model and to establish the interception of precipitation by the canopy (C-i). Daily ET estimates from 2012 to 2016 using the Hargreaves-Samani, Priestley-Taylor, Granger-Gray, and Penman-Monteith (short grass) models were calculated using data from a weather station situated in a 6 ha Miscanthus crop. Results from these models were compared to data from on-site eddy covariance (EC) instrumentation to determine accuracy and calculate the crop coefficient (K-c) model parameter. C-i was measured from June 2016 to March 2017 using stem-flow and through-flow gauges within the crop and rain gauges outside the crop. The closest estimated ET to the EC data was the Penman-Monteith (short grass) model. The K-c values proposed are 0.63 for the early season (March and April), 0.85 for the main growing season (May to September), 1.57 for the late growing season (October and November), and 1.12 over the winter (December to February). These more accurate K-c values will enable better ET estimates with the use of the Penman-Monteith (short grass) model improving estimates of potential yields and hydrological impacts of land use change. C-i was 24% and remained high during the autumn and winter thereby sustaining significant levels of canopy evaporation and suggesting benefits for winter flood mitigation.