Field energy balances frorn irrigated crops (vineyards and mango orchard) and natural vegetation (caatinga) together with a net of agro-rneteorological stations were used to develop a model for lhe surface resistance (r,) to evapotranspiration at the basin scale in the serni-arid region of Brazil for land-use change analyses. It was done to make a historical picture at the municipal-district levei ofvegetation replacement in Pernambuco (PE) and Bahia (BA), Brazil. Although Petrolina, PE and Juazeiro, BA presented the biggest irrigated areas, the incrernents throughout the years (2002-2006) were smaller (213 and 171%) than those for Santa Maria, PE (275%) and for Lagoa Grande da Boa Vista, PE (260%)

TEIXEIRA, A. H. de C.

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Determination of surface resistance to evapotranspiration by remote sensing parameters in the semi-arid region of Brazil for land-use change analyses.

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Remote Sensing and Hydrology (Proceedings 01 a symposium held at Jackson Hole,Wyoming, USA, September 2010) (IAHS Publ. 352, 2012).167Determination of surface resistance to evapotranspiration byremote sensing parameters in the semi-arid region of Brazil forland-use change analysesANTONIO H. DE C. TElXElRAEmbrapa Semi-arid, PO Box 23, 56302-970, Petrolina, Pernambuco, Brazilheribert@cpatsa.embrapa.brAbstract Field energy balances frorn irrigated crops (vineyards and mango orchard) and natural vegetation(caatinga) together with a net of agro-rneteorological stations were used to develop a model for lhe surfaceresistance (r,) to evapotranspiration at the basin scale in the serni-arid region of Brazil for land-use changeanalyses. It was done to make a historical picture at the municipal-district levei ofvegetation replacement inPernambuco (PE) and Bahia (BA), Brazil. Although Petrolina, PE and Juazeiro, BA presented the biggestirrigated areas, the incrernents throughout the years (2002-2006) were smaller (213 and 171%) than thosefor Santa Maria, PE (275%) and for Lagoa Grande da Boa Vista, PE (260%).Key words energy balance; satellite measurernents; water resourcesINTRODUCTIONThe intensification of agriculture in the Low-Middle São Francisco River basin, Brazil, withmainly fruit crops, has caused large land-use changes, with the replacement of the naturalvegetation (caatinga) by large irrigated areas. Water scarcity in some areas and periods of the yearhas been a problem, and the drainage of irrigated agriculture may affect the water quality. Toavoid both water scarcity and water excess, one must have efficient tools to quantify the intensityof these processes.A model to obtain the surface resistance (rs) based on the Penrnan-Monteith equation wasdeveloped and applied to infer the soil moisture conditions for a simplified vegetationc1assification. Landsat satellite images of the study region were layered with the shapes of themain fruit growing regions in the Pemambuco (Petrolina, Lagoa Grande and Santa Maria da BoaVista) and Bahia (Juazeiro and Casa Nova) states, and with a net of seven agro-meteorologicalstations to identify the main direction of the rapid land-use change, highlighting the bestpossibility for the irrigation expansion and to subsidize the agricultural managers in the semi-aridregion of Brazil.MATERIALS AND METHODSData from four energy balance experiments, involving irrigated crops and natural vegetation(Teixeira et aI., 2008), were used to determine r, in field conditions by inverting the Penman-Monteith equation (Allen et aI., 1998), which were further related to the surface parametersobtained from 10 Landsat images for the years 2001-2007 (Teixeira et al., 2009). The equationbelow was then applied for c1assifying irrigated crops and natural vegetation at municipality leveI.r. = exp[ a( :: }[l- NDVI]) + b] (1 )where ao and To are the surface albedo and surface temperature after corrections applyingregression equations between satellite and field measurements have been made (Teixeira et aI.,2009), and NDV! is lhe Normalized Difference Vegetation Index. Figure I shows the goodcorrelation between the field and remote sensing parameters.Copyright © 2012 IAHS Press168 Antonio H. de C. Teixeira9.05.0y = 0.04x .• 2.728.0 W=O.937.0~ 6.0c:4.03.0o 36 72 100 144 180Fig. I Relation for the evapotranspiration resistances and remote sensing pararneters. Surface resistance- r.; To- surface ternperature; (;(0- surface albcdo; NDVI- Normalized Difference Vegetation Index.RESULTS ANO OISCUSSIONFigure 2 shows the satellite overpass images of r, representative for the dry (Fig. 2(a» and for therainy (Fig. 2(b» periods in the semi-arid region cornprised of the net of agro-rneteorologicalstations.r,(sm·') r,(sm·')!>IIOO 800.000 640:1000 480200Il 3201000 160Fig. 2 lmagcs ofthe satellite overpasssurface resistance for lhe region cornpriscd of lhe net of agro-rneteorological stations in the Low-Middle São Francisco River basin. (a) October 2005. (b) January2007.In Figure 2, during the first period, the irrigated crops with much lower values than caatingaare strongly highlighted. In general, the caatinga shows r, values higher than 800 s m-I during thedry period of the year (Fig. 2(a». During the wet period there is more homogeneity over the wholearea, and both irrigated and not irrigated vegetated areas present values of less than 800 s m-I. Therelation of r, with soil moisture shows the suitability for estimating this last important watervariable in serni-arid regions which involve a rnixture of ecosysterns. The maximum values are forcaatinga (average of 1937 s m'). Wine grapes and mango orchards present similar values around130 s rn", while table grapes present the lowest values, averaging 74 s rn' (Teixeira et al., 2008).Considering that the rapid land-use change by the replacernent of natural vegetation withirrigated crops can cause environmental problems, it becomes very important to rnake a historicalpicture ar lhe growing regions levei about this replacernent. Figure 3 presents lhe evolution oftheirrigated areas during the period 2002-2006 for the growing regions involved in the net of agro-Oetermination of surface resistance to evapotranspiration for /and-use change ana/yses 169meteorological stations, by using the c1assified satellite data. The total irrigated areas werecalculated by summing the number of pixels with r, values lower than 800 s m·1 and mu1tiplyingthis number by the area of each pixel. lmages of 2001 and 2003 were interpolated to give thesituation for 2002, and the 2006 image gave lhe situation for that year.Although Petrolina, PE and Juazeiro, BA, present the biggest irrigated areas, lhe incrementsthroughout the years (2002-2006) are smaller (213% and 171%) than those for Santa Maria, PE,(275%) and for Lagoa Grande, PE (260%). The municipality of Casa Nova, BA, showed anintermediate value of 198%, being the best option for irrigation expansion.80004000032000roE-m 24000eu"OQ)ro 16000'"°EoPetrolina LagoaGrandeSantaMariaJuazeiro CasaNovaMunicipalitiesFig. 3 Evolution of irrigated growing areas comprised of the net of agro-rneteorological stations, in theLow-Middle São Francisco River basin.The most important commercially irrigated crops in the semi-arid region of Brazil arevineyards and mango orchards, being the crops primarily responsible for the rapid land-usechange, growing mainly in Petrolina, PE and Juazeiro, BA. Figure 4(a) shows the evolution of theareas with the first crop, while Fig. 4(b) depicts the increment for the second crop in the growingregions of Petrolina, PE, and Juazeiro, BA, based on the data from Brazilian Geographical andStatisticallnstitute (18GE).10000880076006400520040002006 2002YearsMango orchards3500• Petroüna-Pf3100.Juazeiro-BAroE.soeu 2700[I>eu"O2 2300eu'":ê190015002002 2003Vineyards2004 2005 2003 2004 2005 2006Fig. 4 Evolution of cultivated areas with vineyards and mango orchards for the centres of developmentPetrolina, PE/Juazeiro, BA in the Low-Middle São Francisco River basin.In the case of Petrolina, PE, the larger increase is for vineyards, while in Juazeiro, BA, thebiggest area is for mango orchards. The highest increment for the fírst crop was verified between170 Antonio H. de C. Teixeira2003 and 2004 in Petrolina, PE, when the cultivated area increased by 151%. In the case of mangoorchards, the most significant period was from 2005-2006 in Juazeiro, BA (129%). Theagricultural water usage in both growing regions is highly productive. The cities have increased interms of exports, and are good examples of converting marginal savannah land into booming ruraldevelopments; however, planning the expansion of irrigated areas requires irrigation managementand full attention to tools for analysis ofthe regional ET.CONCLUSIONSField radiation and energy balances in natural vegetation and irrigated crops, together with agro-meteorological stations and Landsat images, were used to develop a model to quantify the surfaceresistance to evapotranspiration to infer the soil moisture conditions for a simplified vegetationclassification. The maximum values of surface resistance were for natural vegetation-caatinga(average of 1937 s rn'). Wine grapes and mango orchards presented similar values of around130 s m', while table grapes presented the lowest ones, averaging 74 s m-I. Petrolina, PE, andJuazeiro, BA, were highlighted as having the biggest irrigated areas.The most important commercially irrigated crops in the semi-arid region of Brazil arevineyards and mango orchards, being primarily the crops responsible for the rapid land-usechange, and growing mainly in Petrolina, PE, and Juazeiro, BA. ln the case of Petrolina, PE, thelarger increase is for vineyards, while in Juazeiro, BA, the biggest area is for mango orchards. Thehighest increment for the first crop was verified between 2003 and 2004 in Petrolina, PE, when thecultivated area increased by [51 %. In the case of mango orchards, the most significant period ofincrease was from 2005 to 2006 in Juazeiro, BA (129%).The tools tested and presented here can be operationally tested and implemented to monitorthe increase of irrigated agriculture, so assisting ways to avoid environmental damage in hydrol-ogical basins with increasing land use change.REFERENCESAllen, R. G., Pereira, L. S., Raes, D. & Smith, M. (1998) Crop Evapotranspiration: Guidelines for Computing Crop Wa/erRequirements. Food and Agriculture Organization ofthe United Nations, Rome, Italy.Teixeira, A. H. de C., Bastiaanssen, W. G. M., Ahmad, M. D. & Bos, M. G. (2008) Analysis of energy fluxes and vegetarianoatmosphere pararneters in irrigated and natural ecosystems ofsemi-arid Brazil.J. Hydrol. 362,110-127.Teixeira, A. H. de C., Bastiaanssen, W. G. M., Ahmad, M. D. & Bos, M. G. (2009) Reviewing SEBAL input parameters forassessing evapotranspiration and water productivity for the Low-Middle São Francisco River basin, Brazil Part A:Calibration and validatian. Agric. Fores/. Met. 149,462-476.

Determination of surface resistance to evapotranspiration by remote sensing parameters in the semi-arid region of Brazil for land-use change analyses.

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