Abstract
In the Brazilian semi-arid region, the intensification of agriculture results in a change of natural vegetation by irrigated crops. To quantify the contrast between these two ecosystems, the large-scale values of water productivity components were modelled in Petrolina (PE) and Juazeiro (BA) municipalities. The SAFER (Simple Algorithm For Evapotranspiration Retrieving) algorithm was used to acquire evapotranspiration (ET), while the Monteith's radiation model was applied for estimating the biomass production (BIO). Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images were used together with agro-meteorological data. In Petrolina and Juazeiro, the mean monthly ET values for irrigated crops were 938 and 739 mm∙month−1, with the corresponding ones for natural vegetation of 385 and 194 mm∙month−1.Water productivity (WP) was analysed by the ratio of BIO to ET, defined here as the ratio of the net benefits from the mixed agricultural systems to the amount of water required for producing those benefits. The highest incremental WP values, as a result of the irrigated crops introduction, happened outside the rainy period. More spatial WP uniformity occurred in natural vegetation, when comparing with irrigated crops. The most frequent WP values in Petrolina were between 1.6 and 2.2 kg∙m−3 while in Juazeiro this range was from 1.0 to 1.6 kg∙m−3. The differences between the municipalities can be mainly explained by differences in precipitation and soil water storages conditions, promoting better rainfall use efficiency by the natural vegetation in the first one. The results of the current research are important for appraising the land use change impacts in situations of expanding irrigation areas.
Highlights
Agriculture in river basins of semi-arid regions revels that available water has been creating a boost for the rural economy; one of the biggest consequence of this development is that, other water users will call for an appropriate share of the fresh water resources [1]
For Water productivity (WP) analyses based on actual evapotranspiration (ET), besides this last parameter, one has to quantify biomass production (BIO)
The SAFER, Monteith and SUREAL models have been applied to demonstrate the feasibility of computing the changes in water and vegetation variables when natural vegetation is being replaced by irrigated crops in the Brazilian semi-arid region
Summary
Agriculture in river basins of semi-arid regions revels that available water has been creating a boost for the rural economy; one of the biggest consequence of this development is that, other water users will call for an appropriate share of the fresh water resources [1]. The municipalities of Petrolina (Pernambuco State) and Juazeiro (Bahia State), situated in the semi-arid region of the Brazilian Northeast, are good examples, where intensification of irrigated crops has caused widespread replacement of the natural vegetation (“Caatinga”), affecting the energy exchanges between the vegetated surfaces and the lower atmosphere. Under this dynamic situation, the use of tools for estimations of water productivity (WP) components on a large scale are strongly relevant for supporting policy planning and decision-making about the natural resources uses. Due to sub-optimal crop management and environmental constraints that affect crop growth and limit evapotranspiration, ET is generally smaller than ETp [3]
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