The general objective of the study was to analyze the effects of land cover changes on hydrological processes of the Cachoeira river watershed. The hydrological components selected for analysis were the real evapotranspiration and the mean flow at the exutory of the watershed. Through the Thornthwaite and Mather water balance method, applied sequentially to the period between 1997 and 2010, a monthly series of real evapotranspiration was established. The choice of this method was based on the compatibility of the data required by the method with the hydrometeorological available data. Monthly series of average air temperatures and total precipitations was used to calculate the water balance of Thornthwaite and Mather. The average air temperature data were obtained from the pluviometric station Alto da Boa Vista, located around the watershed. In order to obtain a complete and consistent data series of average air temperatures, a correlation was established of these data with the data from the climatological station of the city of Rio de Janeiro. Through this correlation was possible to confirm the consistency of the series of air temperatures and fill any gaps from 1997 until the year 2010. In this period the monthly series of average air temperatures had a mean of 22,1 Celsius degrees, ranging from a maximum of 27,5 Celsius degrees and a minimum of 17,8 Celsius degrees. The pluviometric data used as reference for the average rainfall over the Cachoeira river watershed, was recorded at the pluviometric station Capela Mayrink, located within the watershed. The consistency of this series has been verified before the other pluviometric stations around the watershed by the method of the double mass, which could confirm the consistency because no deviations were found in the precipitation behavior over time. The average annual precipitation over the watershed was 2.181 mm. The highest estimated values of real evapotranspiration were found in the rainy season, between December and March. The estimated average value of annual real evapotranspiration during the studied period was 1.056 mm, ranging between 1.007 mm and 1166 mm. This average value corresponds to approximately 50 per cent of total annual precipitated, in other words, it is indicated that half of the precipitation over the watershed would return to the atmosphere by the processes of the hydrological cycle. Besides the real evapotranspiration, the water balance also provided an estimation of the water extract of the watershed, calculating components as water deficit, water surplus and soil water storage. The mean monthly flow series at the exutory of the watershed was obtained by referencing the data recorded at the fluviometric stations Capela Mayrink and Itanhangá, both located within the watershed. The data from these stations have gone through a consistency analysis, where their fluviometric levels were verified together and their rating curves were elaborated to represent an adequate adjustment to their liquid discharge measurements. After the consistency analysis, the fluviometric levels data were transformed into flows, through the rating curves. The methodology adopted to generate the flow series at the exutory of the watershed consisted primarily in the extension of the flows series at Itanhangá station through correlation with the flows at Capela Mayrink station. Subsequently, the extended flow series at Itanhangá station was transferred to the exutory location by proportionality between drainage areas. Due to the lack of local data, it was not possible to obtain a mean monthly flow series without gaps. The comparison of the flow data with the precipitation data, obtained for the Cachoeira river watershed, showed a coherent behavior over the years. The annual variation of rainfall in the watershed was accompanied by the flow. It was possible to estimate the changes in land cover during the period from 1988 to 2010 using geoprocessing and remote sensing technologies, available at the extension Spatial Analyst Tool from the software ArcGIS 9.3. In order to obtain this data, a geographic information system was developed for the Cachoeira river watershed, composed by a digital terrain model, obtained from the Shuttle Radar Topography Mission (SRTM), and by ten digital images obtained from the satellite Landsat-5/TM, spaced in average every two years during the studied period. The digital terrain model was used to generate the information grids of Flow direction and Flow accumulation. Through these grids, the watershed and the drainage areas of the fluviometric stations could be automatically delineated. The delimitation of the fluviometric stations drainage areas was done in order to verify the official areas mentioned in the inventory stations of the Brazilian National Water Agency. Although the calculated values did show differences in comparison with the official ones, they were used in the study, considering that the relative errors are minimized when using the same geographic basis. Initially the application of digital processing techniques on satellite images consisted of a combination of bands 5, 4, 3, to form the color composite R, G, B. All images were georeferenced at the same control points in the UTM projection system, using the Datum WGS-84, Zone 23 South. Subsequently the images were classified using the supervised classification maximum likelihood. To characterize the dynamics of land cover over time, two thematic classes were chosen: Forest Area, which has forest cover and others natural features not modified by human activities and Non-Forest Area, which includes urbanized areas and most areas that original feature has been changed as a result of human activities and. The signature samples collected for each training were simple and spatially well distributed, within the region of the studied watershed. Since the supervised classification was an automatic process, the thematic products generated showed errors, identified as isolated cells outside the context of the classes, which left the areas fragmented. In order to work around these errors and provide uniformity of the mapped classes a post-classification process was done on the images by applying a majority filter, which replaces isolated cells based on the majority of their contiguous neighboring cells. Even so, a small portion of the thematic products still showed classification errors, so they were manually edited to become more representative. Ten thematic maps of land cover for the Cachoeira river watershed were generated as products of these processes. The validation of each thematic map classification was verified through the confusion matrix. Considering that only two thematic classes with distinct characteristics were used, the performance of the confusion matrix was tendentious and insufficient to ensure the accuracy of the classification. In order to evaluate the quality of the thematic maps obtained, the thematic map generated for 2010 was compared with the official one, provided by the Municipal Secretariat of Environmental of Rio de Janeiro (SMAC). This comparison could validate the consistency of the thematic map of 2010, believing that the other thematic maps also represent an estimate of the land cover reality from past period. The ten thematic maps could estimate the history of land cover changes on the Cachoeira river watershed. It was observed at the maps that there were changes in the shape of the occupation of the watershed, however, in accordance with the estimated percentages, the evolution of land cover in the watershed had a steady behavior over the years. The consecutive differences found did not exceed the order of 3 per cent. Finally, correlations were established between the variation of the areas with forest coverage and the variation of the selected hydrological components. The result obtained at the real evapotranspiration correlation was satisfactory, which indicates a direct relationship between this hydrological component and the watershed land cover dynamic. However it was not possible to establish a correlation of similar quality with the mean flow. This study could contribute as an exercise to aggregate knowledge about the influence of land cover on hydrological processes over time.