Aiming to subsidize the rational water resources management, four Landsat 8 (L8) images along different conditions of the year 2014 were used for modeling the radiation and energy balances in the mixed agroecosystems inside a Brazilian reference semiarid area. The SAFER algorithm was applied to calculate the latent heat flux (λE); net radiation (Rn) was acquired by the Slob equation; ground heat flux (G) was considered a fraction of Rn; and the sensible heat flux (H) was retrieved by residue in the energy balance equation. For classifying the vegetation, the surface resistance algorithm (SUREAL) was used to estimate the surface resistance to the water fluxes (rs) with threshold values for rs. Clearly, one could see higher λE values from irrigated crops (ICs) than those for natural vegetation (NV) with some situations of heat horizontal advection. The respective λE, H, and G average ratios to Rn for the ICs ecosystem were 64% to 79%, 18% to 28%, and 3%, respectively. For the NV ecosystem, the corresponding fractions were 4% to 37%, 60% to 94%, and 4%, respectively. The algorithms proved to have strong sensibility to quantifying the large-scale energy and mass exchanges by applying L8 images in mixed agroecosystems of semiarid environments.
The region of Ilha Solteira, in the Northwestern of São Paulo State, has been undergoing significant changes in agricultural land use and cover since 2006, as pasture fields have been replaced by sugarcane crop. This drastic change can lead to a disturbance in the energy balance, affecting the local climate. The aim of this paper was to assess some parameters related to the energy balance of Ipê's watershed, that changed since no sugarcane cultivation in 2006 to 2,164 hectares in 2011, occupying 31% of the catchment area with this important energy crop for the economy and the environment of Brazil. This study was carried out using remote sensing combined with weather data and using the SAFER (Simple Algorithm for Retrieving Evapotranspiration) model applied in 9 Landsat images collected between 2003 and 2011. The results showed a wide variation between the components of energy balance and when considering only the sugarcane crop were verified the increase values of ETa (Actual Evapotranspiration), H/Rn (Sensible Heat Flux/Net Radiation), TS (Surface Temperature), Rl↑ (Emitted longwave), Rl↓ (Incidente longwave) and surface albedo after the sugarcane production over these years. On the other hand, the NDVI, λE/Rn (Latent Heat Flux/Net Radiation) and Rn values (data) decreased in the same period. Also there was satisfactory correlation between NDVI and ETa. The SAFER model showed satisfactory results for studies of energy balance applied in the Northwestern of São Paulo State.
The Cabeceira Comprida stream's watershed, located in Santa Fé do Sul, Brazil, is an agroecosystem with great demand of water for the population and agriculture. During the dry season the water demand exceeds the amount generated by the watershed. It is important to know the dynamics of the water above the ground to improve the water resources management. Ten Landsat 8 images were used combined with Northwestern São Paulo State Weather Network data under different thermohydrological conditions of the year 2014 to quantify actual evapotranspiration (ETa), biomass production (BIO) and water productivity (WP) based on ETa. Using the Simple Algorithm for Retrieving evapotranspiration (SAFER) for calculating ETa, the Monteith's radiation model was applied for estimating the BIO and for calculation of WP the ratio of BIO and ETa. The average pixels for ETa, BIO and WP ranged respectively from 0.38 ± 0.35 to 2.05 ± 0.76 mm day-1; 10.15 ± 12.19 to 71.61 ± 35.54 kg ha-1 day-1; 1.89 ± 0.76 to 3.88 ± 0.86 kg m-3. The lower values of ETa (0.38 mm day-1; DOY 220), BIO (10.15 kg ha-1 day-1; DOY 220) and WP (1.89 kg m-3; DOY 204) were obtained in winter, and highest values of ETa (2.05 mm day-1; DOY 364) and BIO (71.64 kg ha-1 day-1; DOY 364) in the summer and WP (3.88 kg m-3; DOY 92) in the autumn. The water productivity components can subsidize the monitoring of the agro-ecosystems, being a useful tool to quantify the annual variability of ETa and BIO.
The use of remote sensing satellite in conjunction with models and meteorological data enable the mapping of biophysical properties of agroecosystems with satisfactory accuracy. The main goal of this research was to determine the spatial-temporal agro-ecological indicators of water productivity in watersheds with different types of land use and occupation, using Landsat 8 images, agro-meteorological stations and application of Monteith and SAFER (Simple Algorithm for Retrieving Evapotranspiration) models to estimate the production biomass (BIO) and the actual evapotranspiration (ET), respectively. Incident global solar radiation (RS ↓) is observed seasonality of radiation during the year. Higher RS ↓levels happen during the first and the last four months, when the Sun is around its zenith positions in the study region. During the natural dry period in the region, the RS↓ is lower because winter solstice time for the Southern Hemisphere, this condition it is verified the reducing in the values of ET and BIO. Average values of biophysical properties for the study period were 0.54, 0.16 and 301 K for Normalized Difference Vegetation Index, albedo and surface temperature, respectively. The highest value of BIO was 105 kg ha-1d-1 and occurred in July 2013. The lowest value was 15.9 kg ha-1d-1 and occurred in October 2014. ET showed a value of 1.65 mm d-1 in the rainy period and 0.64 during the dry period in the study area. The highest average ET occurred in the irrigated area (June 2014), with a value of 1.89 mm d-1 and a maximum of 2.46 mm d-1. WP average for the evaluated period was 3.06 Kg m-3, with the largest value of 4.91 Kg m-3 in June 2013 and a minimum value of 2.45 Kg m-3 in September 2013.
In the northwestern side of the São Paulo state, Brazil, irrigated areas are expanding, because rainfall is not enough to supply the crop water requirements. Under the actual climate and land-use change scenarios, large-scale evapotranspiration (ET) and biomass production (BIO) acquirements are relevant. Eleven Landsat 8 images, from May 2013 to October 2014, were used together with a net of eight agrometeorological stations for modelling these water productivity (WP) parameters in the main agricultural growing irrigated areas inside three hydrological basins in this region. Some of these areas inside of each basin were highlighted for more in-depth WP analyses. The SAFER algorithm estimated the ratio of actual (ET) to reference (ET0) evapotranspiration and this ratio was used for both, to calculate ET and to include the soil moisture effects in the Monteith’s Radiation Use Efficiency (RUE) model. The highlighted agricultural growing regions were Paranapuã, Populina and Santa Rita d’Oeste in the Turvo/Grande basin; Rubinéia, Santa Fé do Sul, Suzanópolis and Ilha Solteira, in the São José dos Dourados basin; and Pereira Barreto and Sud Mennucci, in the Baixo Tietê basin. The highest averages of both ET (1.7 ± 0.9 mm d-1) and BIO (47 ± 31 kg ha-1 d-1) were for Ilha Solteira, while the lowest ones happened in Sud Mennucci (1.3 ± 0.7 mm d-1 and 40 ± 27). These ET and BIO ranges returned WP values varying from 2.2 ± 0.6 to 2.6 ± 0.8 kg m-3, with the higher end of this range happening in the Turvo/Grande hydrological basin. Considering the annual time-scale, crops will consume around 770, 828 and 786 mm yr-1 with the corresponding BIO values of 27, 26 and 25 t ha-1 yr-1, respectively in Turvo/Grande, São José do Dourados and Baixo Tietê. It was concluded that increments in agricultural irrigated areas should be stimulated in the northwestern side of the state, mainly in the first basin, to retrieve good yield with less water use.
Four Landsat 8 images were used together with a net of seven agro-meteorological stations for modelling the large-scale radiation and energy balances in the mixed agro-ecosystems inside a semi-arid area composed by irrigated crops and natural vegetation of the Petrolina municipality, Northeast Brazil, along the year 2014. The SAFER algorithm was used to calculate the latent heat flux (λE), net radiation (Rn) was acquired by the Slob equation, ground heat flux (G) was considered as a fraction of Rn and the sensible flux (H) was retrieved by residue in the energy balance equation. For classifying the vegetation into irrigated crops and natural vegetation, the SUREAL algorithm was applied to determine the surface resistance (rs) and threshold values for rs were used to characterize the energy fluxes from these types of vegetated surfaces. Clearly one could see higher λE from irrigated crops than from natural vegetation with some situations of heat horizontal advection increasing its values until 23% times larger than Rn, with respective average λE ranges of 5.7 (64% of Rn) to 7.9 (79% of Rn) and 0.4 (4% of Rn) to 4.3 (37% of Rn) MJ m-2 d-1. The corresponding H mean values were from 1.8 (18% of Rn) to 3.2 (28% of Rn) and 5.4 (60% of Rn) to 9.2 (94% of Rn) MJ m-2 d-1. Average G pixel values ranged from 0.3 to 0.4 MJ m-2 d-1, representing 3 and 4% of Rn for natural vegetation and irrigated crops, respectively.
The energy balance (EB) components were quantified in a commercial farm with corn crop, irrigated by central pivots, in the Northwestern side of São Paulo state, Southeast Brazil. The SAFER (Simple Algorithm For Evapotranspiration Retrieving) was applied to retrieve the latent heat flux (λE), considering six pivots, covering irrigated areas from 74 to 108 ha. With λE quantified and considering soil heat flux (G) as a fraction of net radiation (Rn), the sensible heat flux (H) was acquired as a residual in the energy balance equation. Seven Landsat satellite images, covering all corn crop stages from 23 April 2010 to 29 August 2010, allowed relating the energy balance components according to the accumulated degree-days (DDac) from the planting to harvest dates. The average Rn values ranging from 5.2 to 7.2 MJ m-2 day-1, represented 30 to 45% of global solar radiation (RG). Considering the variation of the energy balance components along the corn crop growing seasons, the average ranges for λE, H and G were respectively 0.0 to 6.4 MJ m-2 day-1, -1.5 to 6.7 MJ m-2 day-1 and 0.1 to 0.6 MJ m-2 day-1. The fraction of the available energy (Rn - G) used as λE was from 0.0 to 1.3 indicated a good irrigation management, insuring that the water deficit could not be the reason of any yield reduction. Although Rn did not reflected well the crop stages, its partition strongly depended on these stages. λE higher than Rn and the negative H/Rn, happening sometimes along the corn growing seasons, occurred after the vegetative growth and before the harvest times, indicated heat advection from the surrounding areas to the irrigation pivots, which represented an additional energy source for the evaporative process. The models applied here with only the visible and infrared bands of the Landsat sensor are very useful for the energy balance analyses, considering the size of the corn crop irrigation pivots in Southeast Brazil, when subsidizing a rational irrigation water application in corn crop.
Water productivity (WP) of various classes of soil usage from watersheds was estimated using the SAFER - Simple Algorithm For Evapotranspiration Retrieving - algorithm and the Monteith equation to estimate the parameters of biomass production (BIO). Monteith’s equation is used to quantify the absorbed photosynthetically active radiation (APAR) and Actual Evapotranspiration (ET) was estimated with the SAFER algorithm. The objective of the research is to analyze the spatial-temporal water productivity in watersheds with different uses and soil occupation during the period from 1996 to 2010, in conditions of drought and using the Monteith model to estimate the production of BIO and using the SAFER model for ET. Results indicated an increase of 153.2% in ET value during the period 1997-2010, showing that the irrigated areas were responsible for this increase in ET values. In September 2000, image of day of year (DOY) 210 showed high values of BIO, with averages of 80.67 kg ha-1d-1. In the year 2010 (DOY:177), the mean value of BIO was 62.90 kg ha-1d-1, with an irrigated area with a maximum value of 227.5 kg ha-1d-1. The highest incremental values of BIO is verified from the start of irrigated areas equal to the value of ET, because there is a relationship between BIO and ET. The maximum water productivity (WP) value occurred in June/2001, with 3,08 kg m-3, the second highest value was in 2010 (DOY:177), with a value of 2,97 kg m-3. Irrigated agriculture show the highest WP value, with maximum value of 6.7 kg m-3. The lowest WP was obtained for DOY 267, because of the dry season with condition of low soil moisture.
The Nilo Coelho irrigation scheme, located in the semi-arid region of Brazil, is highlighted as an important agricultural
irrigated perimeter. Considering the scenario of this fast land use change, the development and application of suitable
tools to quantify the trends of the water productivity parameters on a large scale is important. To analyse the effects of
land use change within this perimeter, the large-scale values of biomass production (BIO) and actual evapotranspiration
(ET) were quantified from 1992 to 2011, under the naturally driest conditions along the year. Monteith´s radiation model
was applied for estimating the absorbed photosynthetically active radiation (APAR), while the SAFER (Simple
Algorithm For Evapotranspiration Retrieving) algorithm was used to retrieve ET. The highest incremental BIO values
happened during the years of 1999 and 2005, as a result of the increased agricultural area under production inside the
perimeter, when the average differences between irrigated crops and natural vegetation were more than 70 kg ha-1 d-1. Comparing the average ET rates of 1992 (1.6 mm d-1) with those for 2011 (3.1 mm d-1), it was verified that the extra water consumption doubled because of the increments of irrigated areas along the years. More uniformity along the years on both water productivity parameters occurred for natural vegetation, evidenced by the lower values of standard deviation when comparing to irrigated crops. The heterogeneity of ET values under irrigation conditions are due to the different species, crop stages, cultural and water managements.
In the semi-arid areas of Petrolina municipality, Northeast Brazil, irrigated agriculture has replaced the natural
vegetation, being important the quantification of the energy exchanges between the plants and the low atmosphere.
MODIS satellite images and agro-meteorological data for the years of 2010 and 2011 were used together, for modelling
the energy balance components under these conditions. Surface albedo (α0), NDVI and surface temperature (T0) were the
remote sensing parameters necessary to calculate the latent heat flux (λE) and the surface resistance to evapotranspiration
(rs) on a large scale. The daily net radiation (Rn) was retrieved from α0, air temperature (Ta) and transmissivity (τsw),
allowing the quantification of the sensible heat flux (H) by residual in the energy balance. With threshold values for rs, it
was possible to do a simplified vegetation classification. The incident solar radiation (RS↓) partitioned as Rn ranged from
0.40 to 0.51, corresponding respectively to periods after the rainy season and the driest conditions of the year, with the
differences between irrigated crops and natural ecosystem not significant. Considering all periods along the year the
averaged fractions of Rn partitioned as H, were 31 and 78%, for irrigated crops and natural vegetation, respectively,
while as λE the corresponding ratios were 69 and 22%. It was observed heat advection from the dry areas to irrigated
plots, with λE exceeding Rn by 9% during the coldest periods. The models tested here can be used for monitoring the
energy exchanges in agro-ecosystems under conditions of land use and climate changes.
In the Nilo Coelho irrigation scheme, Brazil, the natural vegetation has been replaced by irrigated agriculture, bringing
importance for the quantification of the effects on the energy exchanges between the mixed vegetated surfaces and the
low atmosphere. Landsat satellite images and agro-meteorological stations from 1992 to 2011 were used together, for
modelling these exchanges. Surface albedo (α0), NDVI and surface temperature (T0) were the basic remote sensing parameters necessary to calculate the latent heat flux (λE) and the surface resistance to evapotranspiration (rs) at the large scale. The daily net radiation (Rn) was retrieved from α0, air temperature (Ta) and transmissivity (τsw) throughout the slob equation, allowing the quantification of the daily sensible heat flux (H) by residual in the energy balance equation. With a threshold value for rs, it was possible to separate the energy fluxes from crops and natural vegetation. The averaged fractions of Rn partitioned as H and λE, were in average 39 and 67%, respectively. It was observed an increase of the energy used in the evapotranspiration process inside irrigated areas from 51% in 1992 to 80% in 2011, with the ratio λE/Rn presenting an increase of 3 % per year. The tools and models applied in the current research, can subsidize the monitoring of the coupled climate and land use changes effects in irrigation perimeters, being valuable when aiming the sustainability of the irrigated agriculture in the future, avoiding conflicts among different water users.
The municipality of Petrolina, located in the semi-arid region of Brazil, is highlighted as an important agricultural
growing region, however the irrigated areas have cleared natural vegetation inducing a loss of biodiversity. To analyze
the contrast between these two ecosystems the large scale values of biomass production (BIO), evapotranspiration (ET)
and water productivity (WP) were quantified. Monteith´s equation was applied for estimating the absorbed
photosynthetically active radiation (APAR), while the new SAFER (Simple Algorithm For Evapotranspiration
Retrieving) algorithm was used to retrieve ET. The water productivity (WP) was analysed by the ratio of BIO by ET at
monthly time scale with four bands of MODIS satellite images together with agrometeorological data for the year of
2011. The period with the highest water productivity values were from March to April in the rainy period for both
irrigated and not irrigated conditions. However the largest ET rates were in November for irrigated crops and April for
natural vegetation. More uniformity of the vegetation and water variables occurs in natural vegetation, evidenced by the
lower values of standard deviation when comparing to irrigated crops, due to the different crop stages, cultural and
irrigation managements. The models applied with MODIS satellite images on a large scale are considered to be suitable
for water productivity assessments and for quantifying the effects of increasing irrigated areas over natural vegetation on
regional water consumption in situations of quick changing land use pattern.
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