Events of Heavy Rainfall and Strong Winds in Sao Paulo State, Brazil

The relationships of strong winds and heavy rainfall in Sao Paulo State, Brazil, was investigated. Wind data from Project Elektro/Climatico collected by thirteen Platforms of Data Collection were used. The results showed that in the west sector the occurrence of strong winds was higher in the center and south areas and decreased northwards. In the central sector the occurrence of strong wind episodes was higher southwards while in the litoral it was lower due to probably the lack of wind data collected during the austral summer. In Teodoro Sampaio, Andradina, Santa Rita d'Oeste, Votuporanga (west), Rio Claro, Tatui (central) and Ubatuba (litoral) 15, 18, 28, 12, 11, 7 and 3 extreme events occurred, respectively (maximum wind higher than 20 m s together with rainfall higher than 25 mm day). A case study of an episode of extreme event which occurred in Andradina on 15 October 2009 was examined. Heavy rainfall accompanied with high winds and strong divergence at 200 hPa and ascending motion were observed in the region due to intense convection along a cold front that moved fast over Sao Paulo State. The identification of regions with strong winds and their relation with heavy precipitation must drive electrical energy generation and distribution what is important nowadays. So, the main importance of this research is its applicability to the energy sector.


Introduction
The southeastern region of Brazil (SEB) is the most populous and plays an important role in the economy of the country, being characterized by high industrial activity, agricultural productivity and hydroelectric generation.Episodes of rainstorms with strong winds in this region may have drastic economical and social impacts.Some studies have been made to broach the happening of severe weather in SEB (da Silva & Satyamurty (2001); Fernandez et al. (2001); Lima et al. (2010); Seluchi et al. (2011)).Situations of heavy rainfall and strong winds are very common during summer, but may also occur in the transition seasons as it happens in Itu (30 Sept 1991) (Massambani et al. (1992)) and Indaiatuba (24 May 2005) (www.apolo11.com/tornados.php?posic=dat_20050526-193053.inc) in Sao Paulo State, Brazil.According to the International Panel on Climate Change Four Assessment (IPCC AR4) the extreme events of heavy rainfall and strong winds (including floods) have been more severe and frequent.Groisman et al (2005) and Marengo et al. (2009) detected in SEB an increase in the frequency of extreme rainfall events.Then, there is a need to monitor the meteorological conditions in order to provide information for the management of the impact of adverse climate conditions not only by the civil defense but also by the companies of electric energy.
From years 2008 to 2010 a project (Project Elektro/Climatico) was developed for monitoring the wind at surface in Sao Paulo State which is the most populous and economically important state not only of the SEB, but of the entire country.The areas of study were concentrated particularly in the regions of concession of electric energy northwards in this sector) 176 episodes occurred with a predominant direction from northeast.In the litoral (Ubatuba) the occurrence of events of strong winds was lower than in the other sectors (5 episodes).This may be due to the fact that there are no records of the months of November, December and January which correspond to rainy periods.

Relationships between Episodes of Strong Winds and Heavy Rainfall
In this section the relationships between strong winds and heavy precipitation is investigated.For this purpose the data series from June 2009 to May 2010 is considered.The data of maximum wind are obtained from the dataset of the project (www.dpi.inpe.br/sima/vento)and the data of rainfall is obtained from Instituto Agronomico de Campinas (IAC, www.iac.sp.gov.br).Winds higher than 20 m s -1 (approximately 72 km h -1 ) together with rainfall higher than 25 mm day -1 are assumed as extreme events which may be catastrophic and cause damage for the distribution of electric power and put lives at risk.The cities in the three sectors of the areas of concession of Elektro Ltda.chosen for this analysis are the same that in section 2. Figure 5 shows the distribution of maximum wind and the rainfall for the west sector while Figure 6 presents it for the central and litoral sectors.As can be seen, there were periods when strong winds correspond to approximately peaks of rainfall.However, there were some small number of periods that although the winds were strong the amount of rainfall was low and vice-versa.Figure 6.The same as Figure 5, but for the central sector: a) Rio Claro (01/feb/09-10/may/10), b) Tatui (15/feb/09-10/may/10), and the litoral sector: c) Ubatuba (01/feb/09-22/oct/09 and 12/feb/10-05/may/10) Thus, in order to examine the association of strong winds and the occurrence of rainfall Figure 7 and 8 are prepared.These figures show the distribution of the maximum hourly average (left column) and daily absolute maximum wind (right column) as function of rainfall interval for the west, central and litoral sectors.As can be seen in Figure 7, in the part southwards of west sector (Teodoro Sampaio and Andradina) most of the absolute maximum winds were associated with rainfall between 10-20 mm day -1 and 20-30 mm day -1 .It is also showed in this figure that some maximum wind events are associated with rainfall between 40-50 mm day -1 and 50-75 mm day -1 .In the part northwards (Santa Rita d'Oeste and Votuporanga) the higher concentration of maximum wind was associated with rainfall 5-10 mm day -1 and 10-20 mm day -1 and intense precipitation (more than 30 mm day -1 ) in general is not associated with intense winds.In the central sector most of the maximum winds corresponded to rainfall 5-10 mm day -1 and 10-20 mm day -1 while in the litoral (Ubatuba) it was associated with rainfall 30-40 mm day -1 .The strongest maximum winds occurred in the west sector, followed by central and litoral sectors.2-8 show the dates of extreme events in the cities of the three sectors chosen in section 2. In these dates it was considered that the rainfall and the maximum wind occurred in the former day and in the day earlier.On these intervals of three days it happened at least an occurrence of maximum wind higher than 20 m s -1 and rainfall higher than 25 mm day -1 .As shown in Tables 2-8, in Teodoro Sampaio, Andradina, Santa Rita d'Oeste, Votuporanga, Rio Claro, Tatui and Ubatuba occurred 15, 18, 28, 12, 11, 7 and 3 extreme events, respectively, that are capable of causing damage to distribution of electricity and the people.In the next section a case study of extreme event is chosen to illustrate the impact of meteorological adverse conditions in the regions of concession of Elektro Ltda.Table 2. Occurrence of extreme events in Teodoro Sampaio (west sector).The dates consider the rainfall (mm) and the maximum wind (m s -1 ) occurred in the former day and in the day earlier.In these intervals of three days it happens at least an occurrence of maximum wind higher than 20 m s -1 and rainfall higher than 25 mm day

Figure 7 .Figure 8 .
Figure 7. Distribution of the maximum hourly average (left column) and daily absolute maximum wind (right column) as function of rainfall interval for the west sector: a) Teodoro Sampaio, b) Andradina, c) Santa Rita d'Oeste, and d) Votuporanga.The bars around the values of mean maximum wind represent a interval that includes 80% of the values of maximum wind.The data of maximum wind are obtained from the dataset of the present project and data of rainfall are obtained from IAC (www.iac.sp.gov.br) Figure12far from

Table 3 .
Occurrence of extreme events in Andradina (west sector).Legend similar to Table2