Temperature Surface of Guaíba Lake, RS, from time series of MODIS images
2017
The Guaiba lake is located in an area of complex weather variation and is influenced by many atmospheric circulation systems, bringing about violent occluded fronts, and, sometimes, intense precipitation. In Rio Grande do Sul, during El Nino, air temperatures and the precipitation index are higher, contrary to La Nina. Moreover, the Guaiba Lake receives water from the Guaiba's Hydrographical Region, which corresponds to 1/3 of Rio Grande do Sul State, and is thus an important water body to the metropolitan region of Porto Alegre. Methods that seek to understand the behavior of Guaiba lake surface water temperature (LSWT) may lead to relevant information to identify periods of more or less water warming, as well as the relations between LSWT, water quality deterioration and risks to human health. This paper aims to comprehend the behavior of Guaiba LSWT during periods of climatic anomalies (El Nino/La Nina). Therefore, 418 sea surface temperature (SST) images from the MODIS sensor were processed with SeaDas 7.2 software. The quarterly averages of LSWT were obtained and compared to the climatological anomalies in Equatorial Pacific Ocean. LSWT behavior is more complex in El Nino/La Nina periods. The results show that during climatic abnormality periods there are no direct relationship between the warming/cooling of Guaiba LSWT and the warming/cooling of Equatorial Pacific Ocean’s SST. The precipitation indices were more significant to the behavior of LSWT during El Nino periods, but for all periods (of climatic normality and abnormality), air temperature is what most influences LSWT. This relation occurs with climatic factors of water retention time, water entry and precipitation, and air temperature. There is a major correspondence during La Nina periods with the cooling of Guaiba LSWT only for some years. On the other hand, during El Nino periods there are no correspondences of this phenomenon with the warming of Guaiba LSWT. There are only more intense oscillations in surface temperatures than during regular and La Nina periods, but with a tendency to LSWT warming.
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