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.
This work has as aim to quantify the energy changes between atmosphere and surface by modeling both net radiation and soil heat flux related to land use and cover. The methodology took into account modeling and mapping of physical and biophysical parameters using MODIS images and SEBAL algorithm in an area of native vegetation and irrigated crops. The results showed that there are variations in the values of the estimated parameters for different land cover types and mainly in caatinga cover. The dense caatinga presents mean values of soil heat flux (Go) of 124.9 Wm-2 while sparse caatinga with incidence of erosion, present average value of 132.6 Wm-2. For irrigated plots cultivated with banana, coconut, and papaya the mean Go values were 103.8, 98.6, 113.9 Wm-2, respectively. With regard to the instantaneous net radiation (Rn), dense caatinga presented mean value of 626.1 Wm-2, while sparse caatinga a mean value of 575.2 Wm-2. Irrigated areas cultivated with banana, coconut, and papaya presented Rn of 658.1, 647.4 and 617.9 W m-2 respectively. Applying daily mean net radiation (RnDAve) it was found that dense caatinga had a mean value of 417.1 W m-2, while sparse caatinga had a mean value of 379.9 W m-2. For the irrigated crops of banana, coconut and papaya the RnDAve values were 430.9, 431.3 and 411.6 W m-2, respectively. Sinusoidal model can be applied to determine the maximum and RnDAve considering the diverse classes of LULC; however, there is a need to compare the results with field data for validation of this model.
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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