Variabilidade espaço-temporal de chuvas extremas na bacia hidrográfica do rio São Francisco: uma aplicação conjunta do índice RAI (Rainfall Anomaly Index) e ondaletas.

Abstract

The San Francisco Basin has an important role in the economy of Southeast and Northeast regions of Brazil. Most of its water is aimed to generate electricity and irrigation. Due to the increasing water demand, along with recent episodes of drought (2001-2014), there was a significant change in behavior and management of water resources. This behavior has been evident mainly since 2012, due to drought which led to significant decrease in the level of rivers and reservoirs along the basin. The use of the RAI (Rainfall Anomaly Index) in monthly, quarterly, semiannual and annual scales showed its efficiency in the monitoring of water resources and identification of areas affected by drought, but also allowed to find patterns of atmosphere's behavior in the analyzed years, indicating characteristics applicants with Upper Tropospheric Cyclonic Vortices (UTCV) performance. The studies covered the years 2001, 2007, 2008, 2012 and 2014. The results showed that the performance of UTCV plays a significant role in the behavior of rains, needing to have a greater focus on monitoring the emergence, intensification, displacement and region of operation of these systems. The use of WT (Wavelet Transform) applied to the RAI values reinforced the findings, showing that the intra-seasonal variability is modulated by lower frequency events (annual and decadal scale) and needs to be monitored with the same importance. However, it is necessary to make a more detailed investigation using the WT at a higher resolution, in order to have a better understanding of key atmospheric variables that affect the rainfall regime in the studied region. The WT applied to the values of the quotas from Sobradinho and Três Marias showed that not only climatic factors have influenced the decrease in the volume of the reservoirs, as well as the increased demand and the change in control of these resources especially in recent years.