# **4. The Alto-Tietê River Basin**

Brazil has always been considered a country rich in water. It is estimated that about 12% of the world’s surface water resources are located in the country.<sup>4</sup> Per capita water availability reaches 40,000 m<sup>3</sup> /inhab/year. But this impressive number masks an extremely uneven distribution of water resources among regions.

The Amazon river basin alone, which covers 48% of the country’s territory, accounts for 75% of Brazil’s freshwater resources but houses only 4% of its population. The most dramatic departure from abundance can be found in the Northeast region, which includes most of the semi-arid region of the country. Accounting for 18% of Brazil’s territory and about 28% of its population, this region has only 5% of the country’s water resources and is subject to recurrent, severe droughts, harvest failures and food shortages. With 73% of the country’s population, 11% of its territory, and about 10% of its water resources, the Southeast is the heart of Brazil’s industrial economy and also has the highest agricultural production. This growth has generated increasing pressure on the region’s water resources, due to conflicting demands from multiple users and the steady deterioration of water quality. The current case study is particularly illustrative of the problems faced by water management in highly urbanized and industrialized humid regions in Brazil.

The Tietê —São Paulo state’s largest river— runs 1,100 Km from its eastern source in the São Paulo Metropolitan Region to the western border of the state where it joins the Paraná river, which then runs southward, toward the Rio de la Plata estuary between Argentina and Uruguay (Figure 1).

The Alto-Tietê corresponds to the upper part of the basin, from the headwaters of the Tietê River in Salesópolis city to the Rasgão Reservoir<sup>5</sup> . Most of the Alto Tietê’s urban area lies on sedimentary soils. The climate in the basin is typical of tropical high plain savannas, with a temperate summer. The average temperature in the basin is about 17.8 degrees Celsius, and ranges from annual averages of 13.8 to 24.3 degrees Celsius. Precipitation varies little throughout the basin, averaging at 1,400 mm per year.

The area covered by the Alto Tietê basin is almost coterminous with the Metropolitan Region of São Paulo (RMSP). With a drainage area of 5,985 square kilometers (2.4% of the state’s territory), the basin encompasses 35 of the 39 municipalities and 99.5% of the population of Greater São Paulo. 37% of the basin’s territory is urbanized. Population growth and urban sprawl in Greater São Paulo have been rapid and uncontrolled in recent decades. Currently, despite the tendency toward stabilized population growth in Greater São Paulo, urban sprawl continues to expand as low-income residents are continually expelled from the urban center to the city’s periphery. In 2000, 17.8 million people lived in the basin and estimates are that in 2010, the population will reach 20 million (FUSP, 2002a).

> 4 Surface water availability is 182,600 m3/s, which reaches 272,000 m3/s if one considers the flow from neighboring countries into the Amazon river basin. The total volume of groundwater resources is estimated at 112 billion m<sup>3</sup> . All data presented in this section are from ANA, 2002.

> 5 This document refers to this hydrographic unit as the Alto Tietê “basin”, as it is normally called.

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