Improved Albedo Estimates Implemented in the METRIC Model for Modeling Energy Balance Fluxes and Evapotranspiration over Agricultural and Natural Areas in the Brazilian Cerrado

Abstract

Abstract:In this study we assessed METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model performance to estimate energy balance fluxes and evapotranspiration (ET) in two heterogeneous landscapes in the Brazilian Cerrado, including fluxes and ET in both agricultural and natural vegetation. The estimates were evaluated by comparing them to flux tower data collected over sugarcane (USR site), woody savanna (PDG site) and stricto-sensu savanna (RECOR site) areas. The selection of the study years (2005)(2006)(2007) for USR/PDG sites and 2011-2015 for RECOR site) was based on the availability of meteorological data (to be used as inputs in METRIC) and of flux tower data for energy balance fluxes and ET comparisons. The broadband albedo submodel was adjusted in order to improve Net Radiation estimates. For this adjustment, we applied at-surface solar radiation simulations obtained from the SMARTS2 model under different conditions of land elevation, precipitable water content and solar angles. We also tested the equivalence between the measured crop coefficient (Kc _ec ) and the reference evapotranspiration fraction (ETrF or F), seeking to extrapolate from instantaneous to daily values of actual evapotranspiration (ETa). Surface albedo was underestimated by 10% at the USR site (showing a better performance for full crop coverage), by 15% at the PDG site (following the woody savanna dynamics pattern through dry and wet seasons) and was overestimated by 21% at the RECOR site. METRIC was effective in simulating the spatial and temporal variability of energy balance fluxes and ET over agricultural and natural vegetation in the Brazilian Cerrado, with errors within those reported in the literature. Net radiation (Rn) presented consistent results (coefficient of determination (R 2 ) > 0.94) but it was overestimated by 8% and 9% in sugarcane and woody savanna, respectively. METRIC-derived ET estimates showed an agreement with ground data at USR and PDG sites (R 2 > 0.88, root mean square error (RMSE) up to 0.87 mm day −1 ), but at the RECOR site, ET was overestimated by 14% (R 2 = 0.96, mean absolute error (MAE) = 0.62 mm.day −1 and RMSE = 0.75 mm day −1 ). Surface energy balance fluxes and ET were marked by seasonality, with direct dependence on available energy, rainfall distribution, soil moisture and other parameters like albedo and NDVI.

The interactive pedological-hydrological processes and environmental sensitivity of a tropical isolated wetland in the Brazilian Cerrado

“…In the Brazilian Cerrado, both vegetation type and tillage practices control soil water content and seepage to groundwater [44]. In the core of Cerrado, specifically in the wood savanna located in Águas Emendadas (an experimental area located near Brasília-DF), the estimated evapotranspiration (ETa) varied between 2.48 and 6.56 mm day −1 (an average value of 2.81 mm day −1 for the wet season and 1.70 mm day −1 for the dry season) and the lowest ETa < 1.00 mm day −1 occurs when the soil moisture decreases [45,46]. According to Oliveira et al [46], the increase in grass cover (campo sujo) reduces ETa from 0 to 9 mm day −1 in the dry season to 4.5 mm day −1 in the early wet season.…”

“…In the core of Cerrado, specifically in the wood savanna located in Águas Emendadas (an experimental area located near Brasília-DF), the estimated evapotranspiration (ETa) varied between 2.48 and 6.56 mm day −1 (an average value of 2.81 mm day −1 for the wet season and 1.70 mm day −1 for the dry season) and the lowest ETa < 1.00 mm day −1 occurs when the soil moisture decreases [45,46]. According to Oliveira et al [46], the increase in grass cover (campo sujo) reduces ETa from 0 to 9 mm day −1 in the dry season to 4.5 mm day −1 in the early wet season. The spatial distribution of ETa in the Cerrado is dependent on water availability in the soil and by phenological stage, canopy, geometry, and structure/ depth of the root system vegetation [46].…”

“…According to Oliveira et al [46], the increase in grass cover (campo sujo) reduces ETa from 0 to 9 mm day −1 in the dry season to 4.5 mm day −1 in the early wet season. The spatial distribution of ETa in the Cerrado is dependent on water availability in the soil and by phenological stage, canopy, geometry, and structure/ depth of the root system vegetation [46]. Albeit ETa is a large-range hydro-meteorological variable, the estimated annual mean of ETa in a tropical wetland (East Africa) was 1286 mm, higher than the determined in other landcover classes because this parameter is mostly controlled by water availability [47].…”

Editorial for Special Issue “Remote Sensing Water Cycle: Theory, Sensors, Data, and Applications”

“…Further, this special issue encloses two papers addressing other hydrological components, i.e., evapotranspiration and snowfall. Silva Oliveira et al [9] advanced the albedo estimates for modeling energy-balance fluxes and evapotranspiration over agricultural and natural areas in Brazilian Cerrado; Panegrossi et al [10] utilized the CloudSat-based observation to assess the Global Precipitation Measurement (GPM)'s microwave ability to observe snowfall.…”

“…Besides, remote sensing data enables global and regional hydrological applications, and water resources management, motivates new theories in mapping applications and offers new ways to predict and resolve global water resources conflicts. This Special Issue encompasses a number of contributions in satellite and airborne sensors applications in hydrology, including: mapping theories and applications, i.e., [1][2][3], new methods to better observe hydrological component, i.e., precipitation [4,5], precipitable water vapor (PWV) and vapor pressure deficit (VPD) [6][7][8], energy fluxes and evapotranspiration [9], and snowfall [10], and new methods to improve hydrological decision support system, i.e., [11]. The following section briefs the overall contributions in this Special Issue.…”