Javier Tomasella

The Drought of Amazonia in 2005

Abstract In 2005, large sections of southwestern Amazonia experienced one of the most intense droughts of the last hundred years. The drought severely affected human population along the main channel of the Amazon River and its western and southwestern tributaries, the Solimoes (also known as the Amazon River in the other Amazon countries) and the Madeira Rivers, respectively. The river levels fell to historic low levels and navigation along these rivers had to be suspended. The drought did not affect central or eastern Amazonia, a pattern different from the El Nino–related droughts in 1926, 1983, and 1998. The choice of rainfall data used influenced the detection of the drought. While most datasets (station or gridded data) showed negative departures from mean rainfall, one dataset exhibited above-normal rainfall in western Amazonia. The causes of the drought were not related to El Nino but to (i) the anomalously warm tropical North Atlantic, (ii) the reduced intensity in northeast trade wind moisture tr...

The drought of 2010 in the context of historical droughts in the Amazon region

[1] The year 2010 featured a widespread drought in the Amazon rain forest, which was more severe than the “once‐in‐a‐century” drought of 2005. Water levels of major Amazon tributaries fell drastically to unprecedented low values, and isolated the floodplain population whose transportation depends upon on local streams which completely dried up. The drought of 2010 in Amazonia started in early austral summer during El Nino and then was intensified as a consequence of the warming of the tropical North Atlantic. An observed tendency for an increase in dry and very dry events, particularly in southern Amazonia during the dry season, is concomitant with an increase in the length of the dry season. Our results suggest that it is by means of a longer dry season that warming in the tropical North Atlantic affects the hydrology of the Amazon Rivers at the end of the recession period (austral spring). This process is, sometimes, further aggravated by deficient rainfall in the previous wet season. Citation: Marengo, J. A., J. Tomasella, L. M. Alves, W. R. Soares, and D. A. Rodriguez (2011), The drought of 2010 in the context of historical droughts in the Amazon region, Geophys. Res. Lett., 38, L12703, doi:10.1029/2011GL047436.

Estimating soil water retention characteristics from limited data in Brazilian Amazonia

The application and validation of complex atmosphere-soil water transport models demands knowledge of the parameters that describe hydraulic properties over extensive areas. Such information is rarely available, but Pedo Transfer Functions (PTFs) provide a means of predicting these parameters fro

Hydro-climatic and ecological behaviour of the drought of Amazonia in 2005

In 2005, southwestern Amazonia experienced the effects of an intense drought that affected life and biodiversity. Several major tributaries as well as parts of the main river itself contained only a fraction of their normal volumes of water, and lakes were drying up. The consequences for local people, animals and the forest itself are impossible to estimate now, but they are likely to be serious. The analyses indicate that the drought was manifested as weak peak river season during autumn to winter as a consequence of a weak summertime season in southwestern Amazonia; the winter season was also accompanied by rainfall that sometimes reached 25% of the climatic value, being anomalously warm and dry and helping in the propagation of fires. Analyses of climatic and hydrological records in Amazonia suggest a broad consensus that the 2005 drought was linked not to El Niño as with most previous droughts in the Amazon, but to warming sea surface temperatures in the tropical North Atlantic Ocean.

Trends in streamflow and rainfall in tropical South America: Amazonia, eastern Brazil, and northwestern Peru

Long hydrological records, from the Amazon Basin, northeastern Brazil, and northwestern Peru spanning most of this century, are examined for trends in rainfall (three wettest months) and runoff (three months of highest flow) or stage, where no rating curves exist. Trends are tested for significance using the Mann-Kendall statistic. In basins where large soil, aquifer, or man-made reservoirs give rise to appreciable over-year storage, flows and water levels may be serially correlated. Where serial correlation exists, the usual statistical tests (linear regression, t-test, and Mann-Kendall) will overestimate the significance of trends, showing significance where none exists. Analysis for trend therefore requires particular care when data are serially correlated, and to avoid misleading results, additional supportive evidence must be sought. For example, rainfall records within the same river basin can be checked for trends; serial correlation in rainfall records, in particular, is less likely to be present, so the validity of any trends in rainfall is less open to question. Strong negative trends were found in flow data from the coast of northern Peru and the Sao Francisco River, while positive significant trends were detected in the Parnaiba River basin. No significant trends were found in the discharge or stage records from Amazonia, while rainfall in northeastern Brazil shows a slow increase over long periods. In the Parnaiba and in some rivers of northern Peru unusually large discharges at the beginning or end of the records seem to account for the direction and significance of trends.

The droughts of 1997 and 2005 in Amazonia: floodplain hydrology and its potential ecological and human impacts

It is well known that most of the severe droughts in Amazonia, such as that of 1997, are El Niño-related. However, in 2005, the Amazon was affected by a severe drought that was not El Niño-related, as most of the rainfall anomalies that have happened in southwestern Amazonia are driven by sea surface temperature anomalies in the tropical North Atlantic. Earlier studies have analyzed both droughts in terms of their meteorological causes and impacts in terra firme (non-flooded) forests. This study compares the hydrological effects of both droughts on the Amazonian floodplain and discusses their potential ecological and human impacts based on an extensive literature review. The results revealed that the effects of the 2005 drought were exacerbated because rainfall was lower and evaporation rates were higher at the peak of the dry season compared to the 1997 drought. This induced a more acute depletion of water levels in floodplain lakes and was most likely associated with higher fish mortality rates. Based on the fact that the stem growth of many floodplain species is related to the length of the non-flooded period, it is hypothesized that the 1997 drought had more positive effects on floodplain forest growth than the 2005 drought. The fishing community of Silves in central Amazonia considered both droughts to have been equally severe. However, the 2005 drought was widely broadcasted by the press; therefore, the governmental mitigation efforts were more comprehensive. It is suggested that the availability of new communication technology and greater public awareness regarding environmental issues, combined with the new legal framework for assessing the severity of calamities in Brazil, are among the primary factors that explain the difference in societal response between the two droughts.

Deforestation and conservation in major watersheds of the Brazilian Amazon.

been deforested, and to reduce further losses and preserve the important natural and cultural resources in this region, large conservation areas have been created by the Brazilian government. The present study analysed land cover and land use change in the major watersheds of the Brazilian Amazon, in order to evaluate the current balance between deforestation and conservation of natural areas in the region. The results show that watersheds draining the southern part of the basin have suffered the highest deforestation rates, with the largest losses (8.3‐20% of total basin area) occurring in the Madeira, Tapaj´ os, Xingu, Araguaia and Tocantins river basins. Most largewatershedsalreadyhavesignificantdeforestation in their headwaters, which can affect hydrological functions and ecological sustainability. The greatest allocation of land for conservation was encountered in the Trombetas, Xingu and Negro watersheds, where conservation areas occupied 92.5, 56.9 and 50.6% of the total basin, respectively. While extensive areas of the Amazon biome have been deforested, on the scale of large watersheds there is a positive balance between conservation areas and deforestation, and on average the area delimited by conservation areas is morethanthreetimeslargerthanthedeforestedareas. An analysis by subwatersheds, however, indicates that

Pedotransfer functions for tropical soils

Publisher Summary This chapter compares the performance of well-documented pedotransfer functions (PTFs) developed in tropical soils. The performance is examined in terms of their accuracy, reliability, and utility. The potential effects of bulk density, the selection of independent variables, and the methodology used for deriving the PTFs on their performance are discussed in the chapter. The overall accuracy of PTFs for tropical soils seems to be affected by the presence of soils having low bulk density. Those soils should be treated in a separate group for which PTFs should be derived separately. Considering the wide range of soils to which the PTFs were applied in the study discussed in the chapter, the general performance of PTFs developed for tropical soils is quite acceptable and certainly comparable to that of the PTFs for the soils of temperate regions.

Estimating unsaturated hydraulic conductivity of brazilian soils using soil-water retention data

Studies to predict the impact of deforestation on climate in Amazonia have stimulated interest in the hydraulic properties of the soils of the region and the surrounding areas. Few directly measured hydraulic conductivity data are available; these were used to derive parameters to allow the unsat

Water and Chemical Budgets at the Catchment Scale Including Nutrient Exports from Intact Forests and Disturbed Landscapes

The objective of this chapter is to summarize current understanding of the hydrological function and nutrient dynamics of Amazonian forest derived from work in microcatchments and how these processes are affected by land use and land cover changes, mainly the conversion of forest to pasture. Our conclusions are based on field observations in catchments located in different regions of Amazonia. This chapter is divided into sections that provide (1) a general overview of small catchment research in LBA and then address (2) runoff and water budgets, (3) the influences of soil, vegetation, and riparian zones on stream chemistry and element budgets, and (4) the potential influence of catchment scale on the hydrological and biogeochemical processes that control water and element budgets. The first section provides a background on the principle sites where microcatchments have been studied as part of LBA and the questions that have driven research at these sites. The second section reviews intensive studies of runoff, streamflow, and catchment water balance and how these processes are altered by clearing of tropical forest for pasture. The third section synthesizes what is known about the processes that control the concentrations and export of materials that reach streams via different hydrological flow paths in Amazonian forest and how these processes and flow paths are altered by deforestation and land use change. The fourth section summarizes what we know about how hydrological and biogeochemical processes change with scale and how this understanding can be used to both predict catchment response to land use change and manage Amazonian landscapes to maintain valuable hydrological and biogeochemical functions.