Eloiza Paiva

Time trends in rainfall records in Amazonia

Abstract This paper reports the results of statistical analyses for the detection of time trend in 48 rainfall records from sites in the Amazon Basin with more than 15 yr of record. Using a nonparametric test for trend in monthly rainfall, three results emerge: (a) irrespective of the statistical significance of time trends, positive and negative trends occur with approximately equal frequencies over the Brazilian Amazon hydrographic basin; (b) the number of statistically significant time trends, whether positive or negative of statistically significant time trends, whether positive or negative, is very much greater than can be ascribed to chance variation; (c) significantly negative time trends are more common than significantly positive time trends in monthly rainfall. Over the period of approximately 30 yr covered by the records, during which deforestation has been rapid, negative trends seem to have occurred more frequently in two regions of western and central Amazonia, and positive trends more frequ...

Effect of vegetation and seasons on the water content of soil climatic conditions of the Atlantic Forest in Southern Brazil

The objetive of this work was monitoring of the soil water content behavior, for grass native field and native forest vegetation cover, in an area characteristic of Atlantic Forest in Southern Brazil. To obtain the soil water content, some electronics tensiometers with pressure transducer were utilized and were placed 0.10, 0.30 and 0.70 m below the soil surface, from October 2010 to May 2011. The values of matric potential, measured by tensiometers, were transformed into soil water content values based on a soil water retention curve for each depth. The obtained results showed that in native fields and native forests, the greatest variations of tension, water content, and water storage in the soil happened at a depth of 0.10 and 0.30 m. At a depth of 0.70 m these variables presented less variations, mainly in native field soil cover. The soil water content was greater in the forested land cover than in the native field. Different seasons throughout the year directly influenced the behavior of analyzed variables. In the summer, the values of soil water tension observed in the forested land cover were higher than those observed in the native field. In the winter season, there was a change in that behavior at depths of 0.30 and 0.70 m and the values of soil water tension became smaller than the forested land cover. Great variations in the soil water tension were observed from October to April (summer), and became steady after May (in the beginning of winter). In the grass native field, most of the time, the greatest soil water content was observed at a depth of 0.10 m followed by depths of 0.70 and 0.30 m, respectively. During dry periods, the greatest soil water content was observed at a depth of 0.70 m, followed by depths of 0.10 and 0.30 m, respectively. In the forest, except for rainy periods, the greatest content of the soil water occurred at a depth of 0.70 m. For the conditions of this study, the total storage of water in the soil was 31.05% greater in the native forest than in the native field.

Trends in streamflow in the Ibicuí river basin - influence of rice crop irrigation

The Ibicui basin, located in the south of Brazil, is close to 50,000 km2 in drainage area. The basin has big problems with water deficits, attributed to the indiscriminate use of water to irrigate rice. The objective of this study is a statistical analysis of water flow data in the Ibicui basin to verify if there are significant trends in water availability related to the withdrawal of water for rice crop irrigation. We used data from 11 fluviometric stations for 1970 to 2011, corresponding to the period of major growth in rice cultivation. Records of daily flow data were normalized, then for each month, the flow at durations between 50% to 99% were calculated. Trends in these series were evaluated using the Mann-Kendall test. The results showed that there are trends of increasing water flow for 8 of the 11 stations, and in 6 of those 8 stations the increasing trend was statistically significant. Just 3 stations had negative trends and these were in sub-basins with higher percentage area in rice. Analyzing the trends for several flow durations, it was observed that there was a reduction of the trends with duration. Also, in a river with sequential stations, the significance of trends as reflected by the Mann-Kendall Zs decreased with irrigated area. We conclude that for the Ibicui Basin analysis of trends in the flow data does not clearly reflect the effect of water withdrawals for irrigation of rice.

Scenarios Simulation of the Runoff Response for a Peri-Urban Watershed in the Atlantic Forest Biome, Southern Brazil

Simulating the hydrologic response of a watershed for different scenarios is an important tool for assessing the rational use of the land and natural resources, especially in environments where urbanization is not ever an organized procedure. This study used the Kineros2 event oriented hydrological model to simulate the runoff response of a 4.9 km² urban basin located in the Atlantic Forest biome in Southern Brazil, with 35% of the area being impermeable. The goal of the study was to estimate the characteristic parameters of soils and land cover for the watershed to enable the evaluation of basin response for different land uses. To achieve this objective, the responses of ten measured rainfall-runoff events were used to calibrate five parameters of the model. Two of these events were then used to simulate several scenarios. Using 100% forest land cover as reference, a scenario of 100% pasture land use increases runoff volume by 20% and peak flow by 50%. For the current land use (35% impermeable), the runoff volume is 78% higher and the peak 145% higher than the reference. For a scenario with 57% impermeable area, the runoff volume increases in average 124% and the peak 231%. For the most urbanized condition, with 78% impermeable area, the runoff volume increases in average 214% and the peak flow rate 470%.

Natural flows obtained from a simplified model and the influence of rice irrigation in these flows

This study aimed to apply and assess the simplified methodology used by Paiva et al (2006 b) in a basin of the Vacacai River to obtain information about natural flows. The analyses to determine the water demands of rice farming and to sub-divide the basin were based on hydrological information and use of geoprocessing techniques. The study of use and occupation of the soil showed that the flood plains of the Vacacai River are covered by rice fields that occupy 8.06% of the basin area. Factors such as scarcity of rainfall data as well as uncertainty in the demand value adversity affected the goodness of model fit. However,it was possible to conclude that the methodology was really efficient in determining the natural flow of sub-basins with approximately 3456 km² of area, and that due to factors that were not considered in the model (e.g. spreading into rivers and storage purposes) it was not possible to obtain better results for sub-basins of larger dimensions. Among the ranges of the discretized model, the ones which presented the best results were those with monthly generation and propagation of flow as well as the generation of daily flow and propagation of 7 day average flow, highlighting the monthly simulation due to the smoothing of monthly maximum flows which were not well represented. It was concluded that in areas where the number of rice fields is higher the flows in the fluviometric stations are underestimated, the knowledge about natural flows by managers becomes then relevant.

Classification Of Water Resources In River Basins With Lack Of Data: A Case Study In Southern Brazil

This paper aims at the analysis and development of technical and methodological basis for classification of water resources bodies in river basins with lack of data. It was based on Brazilian’s water quality standard. The Vacacai Mirim River Basin, with 1120 Km2 of drainage area, located between the latitudes -29° 36’ 55” and -29° 39’ 50” and longitudes -53° 46’ 30” and -53° 49’ 29, in southern Brazil was used as a case study. A water usage classifier proposal was presented to the government office for management of water resource of the state of Rio Grande do Sul, which is based on the characterization of the physical environment and the water quality, as well as an estimation of availability and consumption of water. The estimated total water consumption in the basin in 2005 was 141,542,873 m3, being 7.53% for public supply and 92.47% for the irrigation of rice crops. Characterization of the water quality was carried out using QUAL2E model, which applied samples collected on field expeditions at ten spots of the river. Estimation of the natural flow was based on a new simplified methodology based on the SMAP model and on a genetic algorithm to optimization. Input data consisted of the observed flow at the basin’s outlet, and the estimated water consumption for irrigation as well as for public supply. Results have shown that the developed methodology is well suited for basins of rivers subjected to intensive water usage and with limited amount of data.