A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

DOES AN ARTIFICIAL LAKE MODIFIES THE MICROCLIMATE? A CASESTUDY OF THE RAINFALL VARIATIONS AT TUCURUI ´s DAM IN PARA.Fabio SanchesGilberto FischPrograma de Pós-Graduação em Ciências Ambientais da UNITAUe-mail: fosanches@uol.com.brAbstract: There are a lot of concern about the impacts from an artificial lake in Amazoniacan make, especially related with the microclimate. These impacts are not well understoodyet. The rainfall data (daily values) from 1972 up to 1983 (namely prior) from INMET andfrom 1984-1996 (namely post) from ELETRONORTE were used in this work. Comparingthe monthly totals, there is no significant differences between the prior and post periodaccording to statistical tests (Mann-Whitney and/or Fisher Test). Only one month(December) has not failed to pass the hypotheses of equal precipitation at 5% level ofconfidence. Analyzing the occurrence the days with rains higher than 1, 5, 10, 25 and 50mm, the number (and frequency) of light rains has increased, especially during the dryseason. This may be due to the increase of evaporation from the lake. Although the onset ofthe rainy season is controlled by large-scale factors, there is a weak signal that it can startearlier (September) for the post conditions than for the prior conditions (October). Anautoregressive-moving average model (Arma) has been simulated with the prior data-set inorder to identify the influence of the lake. The post conditions (in a monthly scale) matchquite well the forecast data, suggesting that the lake did not modify the characteristic of therain.