Geomorphological changes in the Anthropocene : fluvial systems for evaluating effects of the centenary urbanization processes of SÃO PAULO-BRAZIL.

Cleide Rodrigues (1)

This study presents results of researches that was carried out over the last three decades based on  Anthropogeomorphological approach, i.e. the Anthropocene Geomorphology, that was tested and developed, aiming to identify and measure geomorphological changes that occurred in the urbanization process of the metropolitan region of São Paulo in fluvial systems. Historical time intervals of about a century or less were especially considered, as well fluvial geoindicators of form, materials and processes of fluvial and fluvio-lacustrine systems. The results were obtained for 20 different case studies and spatio-temporal scales based on procedures that combines historical approach in geomorphology, paleohydrology, fluvial geoindicators and retrospective geomorphological mapping. It was possible to identify the origin of geomorphological changes, classifying those changes in  anthropic, non- anthropic, or complex, to measure their magnitude and compare to holocenic pre urban scenarios of processes, forms and materials.

Applying  fluvial  systems as central reference to measure changes in geoindicators  in diferent scenarios of urbanization processes, allowed us to produce numerous and  convergent evidences to   reafirm the necessity on considering  anthropic actions as an independent variable, as important as the independent variables of global climate changes and  tectonic activity. Among other fluvial processes geoindicators, the example of  the variability of extreme peak flows of higher order channels can be citted , which reached  5 to 23 times more than the average of the extreme peak flows historically recorded ,  an increase that is more clearly correlated to the dynamics of anthropic interventions  than to the  regional climate and microclimate variability, both of them well known in São Paulo metropolitan region.

In terms of the discrimination of the nature of the driving forces  of changes,  high levels of  precison were reached for the majority of fluvial observed changes.

The suitability of the utilization of  fluvial systems to measure anthropogenic changes in the Anthropocene was confirmed and appears to be related to some of their particular characteristics, such as:   lower morphological resilience of those systems as responses to the inputs of matter and energy ; their morphological and processes responses tend to occur  in phase with the time scale of human interventions; for the most partof those systems there are the  possibility of their holocenic history being studied with precision;   there are greater availability of historical data in general such as   reports,  maps and iconographic materials  ;  greater possibility of benefiting from advances in interdisciplinary studies such as the branch of paleohydrology, which utilize  accurate tecniques, historical data and  proxy approach simultaneously, among other characteristics.

Finally, it is convenient to state that enhancing precision in the correlation between urban anthropic interventions  and their direct and indirect effects  in fluvial systems, enhance also the  apllied  Earth sciences as a whole, mainly in branches such as  environmental planning , fluvial  restoration and conservation, manegement of  flood risks  as well  forensic analyses, among others.

 

 

• University of São Paulo Brazil