Dry Season Evapotranspiration Dynamics over Human-Impacted Landscapes in the Southern Amazon Using the Landsat-Based METRIC Model

Abstract

Abstract:Although seasonal and temporal variations in evapotranspiration (ET) in Amazonia have been studied based upon flux-tower data and coarse resolution satellite-based models, ET dynamics over human-impacted landscapes are highly uncertain in this region. In this study, we estimate ET rates from critical land cover types over highly fragmented landscapes in the southern Amazon and characterize the ET dynamics during the dry season using the METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. METRIC, a Landsat-based ET model, that generates spatially continuous ET estimates at a 30 m spatial resolution widely used for agricultural applications, was adapted to the southern Amazon by using the NDVI indexed reference ET fraction (ET r F) approach. Compared to flux tower-based ET rates, this approach showed an improved performance on the forest ET estimation over the standard METRIC approach, with R 2 = 0.73 from R 2 = 0.70 and RMSE reduced from 0.77 mm/day to 0.35 mm/day. We used this approach integrated into the METRIC procedure to estimate ET rates from primary, regenerated, and degraded forests and pasture in Acre, Rondônia, and Mato Grosso, all located in the southern Amazon, during the dry season in 2009. The lowest ET rates occurred in Mato Grosso, the driest region. Acre and Rondônia, both located in the southwestern Amazon, had similar ET rates for all land cover types. Dry season ET rates between primary forest and regenerated forest were similar (p > 0.05) in all sites, ranging between 2.5 and 3.4 mm/day for both forest cover types in the three sites. ET rates from degraded forest in Mato Grosso were significantly lower (p < 0.05) compared to the other forest cover types, with a value of 2.03 mm/day on average. Pasture showed the lowest ET rates during the dry season at all study sites, with the dry season average ET varying from 1.7 mm/day in Mato Grosso to 2.8 mm/day in Acre.

Assessment of an Automated Calibration of the SEBAL Algorithm to Estimate Dry-Season Surface-Energy Partitioning in a Forest–Savanna Transition in Brazil

“…On the other hand, results indicate that the SEBAL slightly overestimated daily ET when compared to eddy covariance measurements, which is in accordance with other studies [51,55,61,[95][96][97], with errors ranging between 0.3-0.4 mm day −1 when compared to measurements forced by energy balance closure techniques, and 0.6-0.8 mm day −1 when compared to measurements without energy balance closure. A better performance of the SEBAL at a daily time scale is possibly related to the small fraction of G and ∆S on a daily time scale [92,94], closely relying on the accurate estimates of Λ and R n 24h .…”

Effects of land‐cover changes on the partitioning of surface energy and water fluxes in Amazonia using high‐resolution satellite imagery

“…Studies using this approach have been developed in the Amazon region, but most of them make use of satellite data with medium and low spatial resolution (30 m to 1 km; de Oliveira et al, 2016;de Oliveira et al, 2017;de Oliveira & Moraes, 2013;Khand, Numata, Kjaersgaard, & Vourlitis, 2017;Numata, Khand, Kjaersgaard, Cochrane, & Silva, 2017;Santos, Nascimento, Rao, & Manzi, 2011).…”

Geotechnology in the analysis of forest fragments in northern Mato Grosso, Brazil

“…The NDVI in 1985 showed that the microbasin was covered by forests due to darker shades, and the NDVI values of 0.60 are common in regions of tropical rainforest 22,23 . Negative NDVI values in 2000 and 2015 show reduced native vegetation with soil exposure and watercourses.…”