A Spatial Analysis of the 2008 Itajaí River Valley Disaster

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Figure 1. Map showing urban extents derived from nighttime lights satellite imagery and informal settlements within the Itajaí River Basin and neighboring regions of Santa Catarina State, Brazil in relation to disaster declarations following an extreme rainfall event in November 2008.

The maps discussed in this blog illustrate how biophysical and socioeconomic risk factors—such as terrain, population distribution, settlement patterns, poverty, and governance—can combine to produce high levels of vulnerability to heavy rainfall, flooding, and landslides. The Itajaí River Basin shown in the map above, is the largest basin in Brazil’s southern state of Santa Catarina, covering 16% of the state’s territory (about 15,500 square kilometers) [1-4]. Stretching across the Serra do Mar Mountains to the Atlantic Ocean, the Itajaí-Açu and the Itajaí-Mirim Rivers drain this hilly landscape and meet at the coastal port city of Itajaí. Over three-quarters of the basin’s population of approximately 1 million people are concentrated in the urban areas located in low-lying areas along the river valleys [2, 3]. This regional pattern of urban concentration is revealed by mapping the urban extents derived from nighttime lights satellite imagery (see Figure 1).

In November 2008, the Itajaí region experienced prolonged heavy rains resulting in extensive flooding, multiple landslides, and widespread disaster declarations. The unusual amount and duration of rainfall were caused by  atmospheric blocking influenced by movement of moisture from the Atlantic Ocean and formed by two weather systems—a high-pressure system (anticyclone) and a low-pressure system (cyclone) [3]. The heavy rains in November were preceded by low to moderate rainfall received in previous weeks in September and October 2008. Daily rainfall amounts in November 2008 reached as high as 337 mm in Blumenau and well above 200 mm in many other locations in the region, and mean monthly rainfall for November reached values 350 to 400% higher than average. After a four-day period of heavy continuous rainfall from November 21 to 24, the Itajaí River rose 11 meters at Blumenau. [2]

Map showing the locations of informal settlements in relation to the slope of the terrain. A number of these settlements are situated along waterways and on steep terrain, making them more susceptible to loss and damage from landslides and flooding during heavy rain.

Figure 2. Map showing the locations of informal settlements in relation to the slope of the terrain. A number of these settlements are situated along waterways and on steep terrain, making them more susceptible to loss and damage from landslides and flooding during heavy rain.

About 1.5 million people across the state of Santa Catarina were affected by this extreme event: it is estimated that 51,250 people were displaced, 27,400 people were left homeless, and 135 lives were lost (mostly due to landslides) [2, 3, 5-7]. Sixty three municípios in Santa Catarina declared a state of emergency, 14 municípios declared a state of “public calamity,” and the Port of Itajaí was inoperable for several days [6]. Brazil’s federal government declared an emergency plan of more than US$400 million [2]. As shown in Figure 1, eleven of the 14 municípios that declared a state of public calamity were in the Itajaí region. Ilhota had the highest number of fatalities in the region (26 lives lost). The municípios of Blumenau and Itajaí had the most people injured (2,380 and 1,800 people respectively). The municipality of Itajaí experienced the most damage to residences (28,400 damaged homes). Blumenau and Gaspar had the most people left homeless (5,200 and 4,300 people respectively). [6]

Blumenau is one of the main industrial cities in the region. Historically, the local government of Blumenau has failed to implement an effective social housing policy and to prevent occupation of high-risk areas by low-income people [8, 9]. Low-income people, unable to afford the cost of formal housing, have constructed homes in informal settlements that lack adequate infrastructure, drainage, and services. These informal settlements often occupy areas along waterways and on steep hillslopes, which are highly vulnerable to flooding and landslides.Figure 2 maps Informal settlements in the Itajaí River Basin. Morro Coripós is an example of an informal settlement that expanded on a steep hillside in Blumenau despite the awareness of both local experts and local officials of the area’s very high degree of susceptibility to landslides [8]. In November 2008, the civil defense successfully alerted and evacuated 48 families from the Morro Coripós community before a landslide destroyed their homes on November 20. Subsequent landslides occurred on November 22 and 23, impacting families and damaging houses in the formal settlements further down the hillslope [8].

1. Aumond, J.J., L. Sevegnani, M. Tachini, and L.E. Bacca, Condições naturais que tornam o Vale do Itajaí sujeito aos desastres, in Desastre de 2008 no Vale do Itajaí: Água, Gente e Política, B. Frank and L. Sevegnani, eds. 2009, Fundação Agência de Água do Vale do Itajaí: Blumenau. pp. 22-37.

2. Stevaux, J.C., E.M. Latrubesse, M.L. de P. Hermann, and S. Aquino, Floods in urban areas of Brazil, in Developments in Earth Surface Processes, M.L. Edgardo, Editor. 2009, Elsevier. pp. 245-266.

3. Garcia, C.M., W.F.F. Roseghini, and I.M. Aschidamini, Environmental management planning – considerations about the events occurring in Santa Catarina – Brazil in November 2008. Procedia – Social and Behavioral Sciences, 2011. 19: pp. 487-493.

4. Jacobi, P.R., S.I. Momm-Schult, and N. Bohn, Ação e reação: Intervenções urbanas e a atuação das instituições no pós-desastre em Blumenau (Brasil). EURE (Santiago), 2013. 39(116): pp. 243-261.

5. Frank, B. and L. Sevegnani, eds. Desastre de 2008 no Vale do Itajaí: Água, Gente e Política. 2009, Fundação Agência de Água do Vale do Itajaí: Blumenau. http://www.comiteitajai.org.br/portal/index.php/prevencaoenchentes/aguagentepolitica.html

6. Sevegnani, L., B. Frank, J.C. de Negredo, M.V. Soares, and E.J. Keim, Gente socorrendo gente, in Desastre de 2008 no Vale do Itajaí: Água, Gente e Política, B. Frank and L. Sevegnani, eds. 2009, Fundação Agência de Água do Vale do Itajaí: Blumenau. pp. 110-127.

7. Nicolodi, J.L. and R.M. Petermann, Potential vulnerability of the Brazilian coastal zone in its environmental, social, and technological aspects. Pan-American Journal of Aquatic Sciences, 2010. 5(2): pp. 12-32.

8. Bohn, N., V. da Silva, and E.C. Bevian, A responsabilidade civil do estado por omissão frende ao desastre, in Desastre de 2008 no Vale do Itajaí: Água, Gente e Política, B. Frank and L. Sevegnani, eds. 2009, Fundação Agência de Água do Vale do Itajaí: Blumenau. pp. 156-165.

9. Siebert, C., (Des)controle urbano no vale do Itajaí, in Desastre de 2008 no Vale do Itajaí: Água, Gente e Política, B. Frank and L. Sevegnani, eds. 2009, Fundação Agência de Água do Vale do Itajaí: Blumenau. pp. 38-51.
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This blog is part of the Map of the Month blog series produced by the Center for International Earth Science Information Network (CIESIN). These maps were made by geographic information specialist Erin Doxsey-Whitfield. Commentary was written by senior research associate Sandra Baptista, with associate research scientist Susana Adamo.

 


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