Satellite-based crop coefficient and regional water use estimates for Hawaiian sugarcane

Abstract

a b s t r a c tWater availability is a major limiting factor for sustainable production of potential biofuel crops in Maui, Hawaii, USA. It is essential to improve regional, near-real time estimates of crop water use to facilitate optimal water management. Satellite remote-sensing offers multiple methods to estimate water management, however, most approaches assume a spatially homogeneous regional meteorology, which does not apply in Hawaii due to strong orographically-induced variations in climate. Canopy ground cover (f c ) and spectral reflectance were measured over two sugarcane fields on the satellite Landsat 7 overpass dates. A strong linear relationship between satellite-based Normalized Difference Vegetation Index (NDVI) values and f c was found (R 2 = 0.97). Canopy ground cover was also found to be highly correlated to crop coefficient (K c ) which was calculated from reference evapotranspiration (ET 0 ) and sugarcane crop evapotranspiration (ET c ) observations from the Eddy Covariance towers. Spatial ET 0 for the entire sugarcane plantation was determined from an automated weather station network previously installed by the commercial grower of the plantation. Regressions were used to convert the satellite NDVI to K c maps, and then the satellite-based ET c maps were created from the satellite-based K c maps and ET 0 values computed and interpolated from the weather station network. To compare with the satellite-based crop coefficient/reference ET method, ET c and K c were also estimated using a satellite-based surface energy balance technique, the METRIC model. These two satellite-based methods were correlated fairly well (R 2 = 0.84 for K c and 0.81 for ET c ). Compared to the METRIC model, the satellite-based crop coefficient/reference ET method may be more practicable for estimating crop water use in Maui, where ground-based ET 0 measurements are available through the on-site automated weather station network with right choice of reference ET equation.Published by Elsevier B.V.

Comparative Analysis of METRIC Model and Atmometer Methods for Estimating Actual Evapotranspiration

“…Figure 8 shows the variation of ET a -METRIC values throughout the growing season at three sites. These results are in agreement with [13,20,62]; they reported high ET values at mid-season stage and low ET values at the end of the growing season in agricultural crops using the METRIC model.…”

“…The ET a maps developed by the METRIC model in this study were similar to other ET maps generated by the METRIC model and reported by Chávez et al [13], Santos et al [24], Folhes et al [18], Droogers et al [62], Healey et al [15], Zhang et al [20], and Carrillo-Rojas et al [63], where they reported the spatial and temporal distribution of daily ET a for different crops including corn. In other situations, Chávez et al [13] reported maximum ET a values (14.1 mm day −1 ) due to high wind speed values (7.0 m s −1 ) at the time of satellite overpass in corn field in Texas High Plains, USA.…”

“…In Maui Island, USA, for example, Anderson et al [67] and Zhang et al [20] reported high variation in evapotranspiration due to high wind speeds values in sugarcane fields. Our results are similar to results reported by Westerhoff [68], who found that as the wind speed increases the ET a values slightly increase.…”

“…Previous studies have compared METRIC model outputs to other methods of ET a estimation such as weighing lysimeter [10], soil water balance [13], Bowen Ratio Energy Balance System (BREBS) [14][15][16][17], Eddy Covariance (EC), for example, [18][19][20][21], Large Aperture Scintillometer (LAS) [22], and the METRIC-MODIS method [23]. These studies showed from moderate to strong relationships between observed and METRIC-estimated ET a , indicating that the METRIC model is a useful tool for estimating accurate ET a at local and field scales.…”

Estimation of Crop Evapotranspiration Using Satellite Remote Sensing-Based Vegetation Index

“…Crop coefficients derived from remotely sensed vegetation index also have used to generate local and regional ET c maps [2,[32][33][34]; however, in northern Mexico, ET c maps using satellite remote sensing-based vegetation index remain unexplored.…”