Are recent frequent high floods in Madeira river basin in Amazonia due to increase in total rainfalls in the Bolivian part of the Basin?

Ana Luisa Nunes de Alencar Osorio, Renato Souza Amorim, Priscilla Medeiros

Tuesday 30 june 2015

17:54 - 17:57h at North America (level 0)

Themes: (T) Extreme events, natural variability and climate change, (ST) Hydrological extremes: floods and droughts, Poster pitches

Parallel session: Poster pitches: 7I. Extreme - Flood Drought

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 to 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 extract 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 maximum annual flow in m3/s from 1967 to 2014, maximum annual monthly total rainfall and 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 . The change in variance was assessed by different sequential methods. The analysis reveals that:The recent incidences of high floods in The Madeira river are results of an increasing trend in the river flow;The maximum annual-monthly-rainfall also show increasing monotonic trend and shifts in variance. Given this results, we can infer that there is a relation between the increase in the extreme floods and the increase of the total rainfall in Bolivian Part of the the Basin.