THE BAURU FLASH FLOOD OF 8 FEBRUARY 2001 AND OPTIONS FOR IMPROVED WARNINGS

Sep 8, 2026

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Severe convective storms in São Paulo frequently produce local flooding, crop and property damage, hail, and wind-driven impacts, creating a strong need for reliable alerting. This study analyzes the Bauru flash flood on 8 February 2001 using two S-band Doppler radars and operational numerical models. Radar thresholds based on reflectivity and vertically integrated liquid water content are evaluated within a synoptic context featuring a deep cyclone, strong low-level moisture, and intense vertical shear. Results support options to improve warning lead times from hours to near-term nowcasting.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages4

Reading Time10 min

AccessFree to download

1. Introduction

2. Synoptic Situation in February 2001

3. Radar Observations

P4C.1 THE BAURU FLASH FLOOD OF 8 FEBRUARY 2001 AND OPTIONS FOR IMPROVED WARNINGS Gerhard Held1 and Jorge Luis Gomes2 1 Universidade Estadual Paulista, Bauru S. P. , Brazil 2 Centro de Previsão do Tempo e Estudos Climáticos, Cachoeira Paulista, S. P. , Brazil 1. INTRODUCTION In the State of São Paulo, located in the south-east of Brazil, severe convective storms frequently cause local flooding in towns and/or devastation of crops and property due to hail or wind storms (microbursts), resulting in many millions of US Dollar damage annually, loss of lives and leave many persons injured (Gomes et al. , 2000; Held et al. , 2001) . Therefore, it is of prime importance to develop an effective alert system for the occurrence of these severe storms, ranging from a couple of days (based on model outputs) to one to three hours ahead (nowcasting, using radar information) of these events. The Meteorological Research Institute (IPMet) of the University of the State of São Paulo (UNESP), based in the geographic center of the State in the town of Bauru, operates a network of two S-band Doppler radars for continuous precipitation monitoring in the State of São Paulo (Figure 4), which provided the ideal tools for such a pilot study. The Bauru radar is located at Lat: 22° 21’28” S, Lon: 49° 01’36”W, 624 m amsl, while the second radar is in Presidente Prudente, 240 km west of Bauru (275° azimuth), at Lat: 22° 10’ 30” S, Lon: 51° 22’ 22”W, 460 m amsl. Both have a 2° beam width and a range of 450 km for surveillance (0° PPI every 30 min), but when operated in volume-scan mode every 15 minutes (or less) it is limited to 240 km, with a resolution of 1 km radially and 1° in azimuth, recording reflectivities and radial velocities. The reflectivity threshold for this study was set at 10 dBZ. Both radars have Sigmet processors and run under the IRIS Operating System, featuring an automatic alert, which is primarily based on the Vertically Integrated Liquid water content (VIL) and reflectivity threshold (the trigger is set to 40 dBZ above 3.5 km with VIL of ≥3 mm over at least 5 km2) . The operational Eta model (Black, 1994) is run by the Center for Weather Forecast and Climatic Studies (CPTEC) twice daily (00 & 12 UTC) for the South American continent and initiated with the NCEP analysis (resolution T62L28; ca 200x200 km) . On the boundaries it is updated with the CPTEC Global Model forecasts. The output has a resolution of 40x40 km, for every 6 hours up to 72 hours ahead. The Meso Eta model (Staudenmaier, 1996), running in non-hydrostatic mode, is also initialized with the NCEP analysis, but the boundary conditions are updated with the CPTEC/Eta operational model (resolution 40x40 km) . Its domain is 1300x840 km and can be centered over any point. The output resolution is 10x10 km, with variable output Corresponding author address: Gerhard Held, Instituto de Pesquisas Meteorológicas, UNESP, CX-281, 17001- 970 Bauru, S. P. , Brazil; e-mail: [gerhard@ipmet.unesp.br](gerhard@ipmet.unesp.br) intervals up to 72 hours ahead. For this case study, the model domain was centered over Bauru with output every 3 hours. 2. SYNOPTIC SITUATION IN FEBRUARY 2001 The beginning of February 2001 was characterized by synoptic situations typical for summer in the interior of the State of São Paulo. In broad terms, it can be summed up by a high pressure system situated off the coast between the State of São Paulo and southern Brazil and ridging in over the continent, with a weak cold front extending along its northern flank across Rio de Janeiro into Minas Gerais. The other component was a large cyclone initially centered over north-western Argentina from where a tongue of moist air extended across Paraguay, Paraná and the State of São Paulo into Mato Grosso do Sul. An other important fact was the strong confluence of wind in the 700 hPa level over the State of São Paulo, overlaid by an exceptionally strong divergence ≥ 500 hPa. The deep cyclone, which

FAQs

Why is an effective warning system important for severe storms in São Paulo?

Severe convective storms often trigger rapid local flooding, hail, and wind impacts that cause large annual economic losses, injuries, and deaths. The document emphasizes the need for timely alerts ranging from days ahead to one to three hours ahead.

What radar setup was used to monitor precipitation?

The study used two S-band Doppler radars in Bauru and Presidente Prudente for continuous monitoring and surveillance. The configuration includes reflectivity and radial velocity recording, with a reflectivity threshold set at 10 dBZ.

How did the storm leading to the 8 February 2001 flood evolve?

Storms developed within the radar range and intensified rapidly, with increasing cell growth and merging into larger complexes. Around 18:00 LT, new development within the 50 km range threatened Bauru, and the updraft collapse led to rapid heavy precipitation and flooding.

Sep 8, 2026

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