ARE RECENT HIGH FLOODS IN MADEIRA RIVER BASIN IN AMAZONIA DUE TO INCREASE IN TOTAL RAINFALLS IN THE BOLIVIAN PART OF THE BASIN

摘要

The homes of more than 5,000 Brazilian families were flooded when the Madeira river overflowed its banks at the beginning of the year of 2014. BR-364, which is a road across the rainforest, was obstructed for almost a month, cutting off the neighbouring state of Acre by land, causing shortages in food and fuel supplies. Because of this high flood, discussions arised about the possible causes of this "atypical' event". Whilst the population blamed the recently constructed dams of Santo Antonio and Jirau, the Authorities blamed the heavy rainfalls in the Bolivian part of the river Basin. Regarding this scenario, this study was developed in order to assess the behavior of the increase in the water flow and rainfalls by analyzing possible trends in the recorded data. The idea was evaluate whether this recent high flood is an indication that the Madeira river floods are getting worse, and if so, if it is partly due to an increase in extreme rainfalls over the Bolivian part of the river basin. To do so, we extracted river flow data from the Porto Velho's station and rainfall data from the gridded VasClimo 50 set from the Global Precipitation Project. The variables analysed were the annual total rainfall from 1951 to 2010. This series were tested for monotonic trends and possible shift in the series variance and mean. The magnitude of trends was calculated using the non-parametric Sen's slope estimator and the Linear Regression Model and the statistical significance was estimated using the Mann-Kendall test with 5% of significance level. Abrupt changes in the mean and variance were assessed by Cumulative Sum Method (CUSUM) and F test using a reduced series generated by Principal Component Analysis (PCA). The analysis reveals an increasing monotonic trend in the river flow data and total annual rainfall and an abrupt change in the mean values of the Principal Component of Annual Rainfall after 1975. Given this results, we can infer that there can be a relation between the increase in the extreme floods and the increase of the total rainfall in Bolivian Part of the basin.