Proceedings Article | 14 October 2015
KEYWORDS: Agriculture, MODIS, Soil science, Vegetation, Magnesium, Climatology, Ecosystems, Heat flux, Radon, Remote sensing
Minas Gerais state, Brazil, has experienced severe water scarcity in some areas, demanding large-scale water balance studies to subsidize water policies. The reflectance bands from the MOD13Q1 MODIS product were used together with gridded agrometeorological data in the state, during the year 2014, later extracting the main agriculture growing regions, North, Northwest and Minas Triangle, for analyzes. Precipitation (Prec) and reference evapotranspiration (ET0) data from 36 weather stations were interpolated, while for actual evapotranspiration (ET), the SAFER (Simple Algorithm for Evapotranspiration Retrieving) algorithm was used. Two climatic water balance indicators were applied, the Water Balance Ratio (WBr = Prec/ET) and the Water Balance Difference (WDd = Prec - ET). The daily net radiation (Rn) was retrieved from surface albedo (α0), air temperature (Ta) and shortwave atmospheric transmissivity (τsw), while the ground heat flux (G) was estimated as a fraction of Rn. For surface moisture, the evapotranspiration ratio (ETr = ET/ET0) and the evaporative fraction [Ef = λE/(Rn - G)] were used, with the latent heat flux (λE) obtained by transforming ET into energy units. Analyzing WDr and WDd, the most water scarcity critical MODIS 16-day periods, reaching to minimum values lower than 1.0 and -10 mm, respectively, were from the end of April to the middle of October. Higher water availability, detected by these indicators larger than 1.5 and 10 mm, respectively, were from the middle of October to the end of December. The maximums WDr and WDd of 7.0 and 158 mm happened from the middle of November to the start of December in the Northwest agricultural growing region. However, according to the ETr and Ef values, after this period, the soil moisture storage showed a gap, increasing only in the second half of December, when they reached to averages of 0.63. The largest values of these last soil moisture indicators, above 0.70 in May, did not coincided with the period of higher Prec, but with the lowest atmospheric demands in all agricultural growing regions, due to a lapse time between the rainfalls and the variation of soil moisture storage. In addition, irrigation should plays a hole in the large-scale water balance. The indicators tested here can be implemented in the Southeast Brazil, for water policies under the actual conditions of water scarcity and competition among water sectors. It was demonstrated the potential to monitor the water conditions for the 16-day periods on a large scale by combining surface-based weather measurements with MODIS remote sensing products.
