Using remote sensing to evaluate the spatial variability of evapotranspiration and crop coefficient in the lower Rio Grande Valley, New Mexico

Abstract

Pecan is a major crop in the lower Rio Grande Valley (LRGV), New Mexico. Currently, about 11,000 ha of pecan orchards at various stages of growth are consuming about 40% of irrigation water in the area. Pecan evapotranspiration (ET) varies with age, canopy cover, soil type and method of water management. There is a need for better quantification of pecan ET for the purpose of water rights adjudication, watershed management and agronomical practices. This paper describes a process where remote sensing information from Landsat-5 and Landsat-7 were combined with ground level measurements to estimate pecan ET and field scale actual crop coefficient (K c ) for the LRGV. The results showed that annual pecan water use for 279 fields ranged from 498 to 1,259 mm with an average water use of 1,054 mm. For fields with NDVI [ 0.6 (normalized difference vegetation index), which represented mature orchards (total of 232 fields), the annual water use ranged from 771 to 1,259 mm with an average water use of 1,077 mm. The results from remote sensing model compared reasonably well with ground level ET values determined by an eddy covariance system in a mature pecan orchard with an average error of 4% and the standard error of estimate (SEE) ranging from 0.91 to 1.06 mm/day. A small fraction (5%) of the pecan fields were within the range of maximum ET and K c .

Evaluation of Spatial and Temporal Root Water Uptake Patterns of a Flood-Irrigated Pecan Tree Using the HYDRUS (2D/3D) Model

“…Sammis et al (2004) reported that the total seasonal ET c of a 30-year-old mature flood-irrigated pecan, measured with the eddy covariance (OPEC) system, ranged from 117 to 126 cm for the growing season of April through November. Samani et al (2009) estimated the pecan seasonal ET c using remote sensing, and the maximum seasonal ET c was 109.5 cm for the growing season of April through October.…”

Estimation of Energy Balance Components over a Drip-Irrigated Olive Orchard Using Thermal and Multispectral Cameras Placed on a Helicopter-Based Unmanned Aerial Vehicle (UAV)

“…Carrasco-Benavides et al [13,14] and Samani et al [15] have demonstrated that remote sensing energy balance (RSEB) models can be used to estimate the spatial variability of LE or ETa over sparse canopies such as orchards and vineyards. Several RSEB algorithms that vary in complexity compute ETa (mm h´1) as residual from the energy balance (EB) equation [16][17][18][19][20][21][22][23]:…”

Assessment of a Remote Sensing Energy Balance Methodology (SEBAL) Using Different Interpolation Methods to Determine Evapotranspiration in a Citrus Orchard

“…As González-Dugo et al (2009) described, daily scaling is generally performed by assuming the conservation of a scaling factor determined at the snapshot time, such as the evaporative fraction (Crago and Brutsaert 1996) or the ratio of ET to ET o (Allen et al 2007a). These assumptions have been applied in sparse woody canopies such as pecan (Samani et al 2009) and olive (Santos et al 2012). However, Ferguson et al (2010 identified the constant ET to ET o ratio approach as a major source of uncertainty in the remote sensing based energy estimates, particularly for agricultural systems different than homogeneous grasslands where a low degree of canopy coupling with the surrounding atmosphere exists (Jarvis 1985).…”