Geo-environmental analysis and identification of degraded areas susceptible to desertification in a semi-arid, tropical ecozone: the Acaraú river basin in northeastern Brazil - Nascimento, Flávio Rodrigues do; Cunha, Sandra Baptista da; Rosa, Morsileide Freitas; Souza, Marcos José Nogueira de (Sociedade & Natureza, 2005)