L. Xavier

Urban climate and clues of heat island events in the metropolitan area of Rio de Janeiro

This paper aims to map the thermal field in the metropolitan region of Rio de Janeiro (MARJ) considering the atmospheric characteristics and the land use that contribute to understanding the urban heat island. Three thermal maps are defined through the use of Landsat5-TM satellite images for three winter events chosen for the decades of 1980, 1990, and 2000, respectively. The results reveal a concentration of warmer cores in urban central areas as well as some local warmer areas in suburban region. Sites with lower temperatures correspond to vegetated areas which are away from the central part of the MARJ, including points of suburban areas. This work emphasizes the importance of the combined analysis of surface temperature with land use and atmospheric conditions, depicting a distinct pattern of heat islands for tropical climate.

Comparisons of observed and modeled elastic responses to hydrological loading in the Amazon Basin

In large hydrological basin, water mass loading can produce significant crustal deformation. We compare the monthly vertical component of 18 GPS sites located in the Amazon basin, with the deflection models derived from GRACE observations in the one hand, and derived from HYDL, a global hydrological model, in the other hand. The GPS dataset includes the largest deflections by hydrological loading ever recorded at two stations located in the center of the basin. The main result of the study is that the GRACE solution produced by GRGS (Groupe de Recherche en Geodesie Spatiale, Toulouse, France) produces the best agreement with the GNSS series with a correlation coefficient up to 0.9 in the center of the basin although 70% at best of the RMS variation in the GPS series is accounted.

Climatological and hydrological patterns and verified trends in precipitation and streamflow in the basins of Brazilian hydroelectric plants

This study focuses on investigating possible changes in hydrometeorological behavior on important Brazilian river basins for power generation purposes. Thereby, this research analyzes the historical averages and observed trends regarding rainfall and streamflow and their impact on the hydrological regime. Ten river basins were selected for the assessment of alterations in the precipitation and streamflow series throughout descriptive measures and statistical significance tests (Mann-Kendall and Sen’s slope). These data are available over different time spans, but most of the records include information from 1961 to 2006. As long as these river basins are subjected to different climate types, their corresponding rainfall and streamflow patterns vary accordingly the basin location in the country, in addition to the season. Most of the country has a predominantly tropical climate, with a wet period concentrated between October and March and a dry period between April and September. Some exceptions are the Northeastern region, where the climate is semi-arid, besides the Southern region, where there is abundant precipitation throughout the year. According to the obtained results, it could be noted that the streamflow response to precipitation is faster in the smaller river basins, what can be due especially to the water travel time. It was found that Belo Monte basin, in Northern Brazil, presents a statistically significant reduction in the annual rainfall. Furthermore, a significant decrease in the annual streamflow was also identified in Xingó and Sobradinho basins, in the Northeastern region. In contrast, Itaipu basin, located in Southern Brazil, showed increasing statistically significant trends in annual rainfall and streamflow during the second half of the twentieth century. Relevant decreasing trends were also identified in the minimum streamflows of the Brazilian Northern and Northeastern basins and increasing ones in the maximum streamflows in the Southern region basins. The results obtained in this work will support the assessment of the impact of rainfall and streamflow future scenarios in regulating capacity of the hydroelectric power plant reservoirs.

Soil Moisture and Soil Water Storage Using Hydrological Modeling and Remote Sensing

Soil moisture and soil water storage play a significant role in lumped and distributed hydrological simulation, both for model initialization and in later time steps to control and to correct model performance. On the other side, rainfall-runoff models still need to be improved to simulate reasonably well the vertical exchanges of heat and water between the soil and the atmosphere, that may result in inconsistent soil moisture fields. Therefore, many issues remain to be adequately addressed, such as how to include new data sources as well as how to improve methods for calibration, validation, parameterization and upscaling of hydrological models. This work focuses on relatively new data sources, addressing the supply of soil moisture (Soil Moisture Experiment 2003 – SMEX03) and soil water storage information (GRACE – Gravity Recovery and Climate Experiment) to a typical lumped rainfall-runoff model (SMAP – Soil Moisture Accounting Procedure running at daily and monthly steps) from in situ measurements and remotely sensed imagery for the Sao Francisco and Amazon basins in Brazil. In particular, a sensitivity analysis is conducted to evaluate jointly both hydrological simulations and data collected and acquired for the studied areas highlighting soundly based and good results and also pointing out some of the challenges to be faced in the near future. We should mention that much more work on soil physics is still necessary for applications regarding rainfall-runoff models to work properly at the watershed scale.