Wagner R. Soares

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.

Climatology of the Low-Level Jet East of the Andes as Derived from the NCEP–NCAR Reanalyses: Characteristics and Temporal Variability

Abstract A climatology of the South American low-level jet east of the Andes (SALLJ) is developed using the 1950– 2000 circulation and moisture fields from the NCEP–NCAR reanalyses and available upper-air observations made in Bolivia and Paraguay since 1998. Upper- and low-level circulation fields were derived for seasonal means and SALLJ composites during the warm and cold seasons. The Bonner criterion 1 was applied for sites in central Bolivia and downstream near northern Paraguay, to determine the spatial and temporal characteristics of the SALLJ. On the circulation characteristics, SALLJ composites during the warm season show the enhanced low-level meridional moisture transport coming from equatorial South America as well as an upper-level wave train emanating from the west Pacific propagating toward South America. The intensification of the warm season SALLJ follows the establishment of an upper-level ridge over southern Brazil and a trough over most of Argentina. The circulation anomalies at upper a...

Development of regional future climate change scenarios in South America using the Eta CPTEC/HadCM3 climate change projections: climatology and regional analyses for the Amazon, São Francisco and the Paraná River basins

The objective of this study is to assess the climate projections over South America using the Eta-CPTEC regional model driven by four members of an ensemble of the Met Office Hadley Centre Global Coupled climate model HadCM3. The global model ensemble was run over the twenty-first century according to the SRES A1B emissions scenario, but with each member having a different climate sensitivity. The four members selected to drive the Eta-CPTEC model span the sensitivity range in the global model ensemble. The Eta-CPTEC model nested in these lateral boundary conditions was configured with a 40-km grid size and was run over 1961–1990 to represent baseline climate, and 2011–2100 to simulate possible future changes. Results presented here focus on austral summer and winter climate of 2011–2040, 2041–2070 and 2071–2100 periods, for South America and for three major river basins in Brazil. Projections of changes in upper and low-level circulation and the mean sea level pressure (SLP) fields simulate a pattern of weakening of the tropical circulation and strengthening of the subtropical circulation, marked by intensification at the surface of the Chaco Low and the subtropical highs. Strong warming (4–6°C) of continental South America increases the temperature gradient between continental South America and the South Atlantic. This leads to stronger SLP gradients between continent and oceans, and to changes in moisture transport and rainfall. Large rainfall reductions are simulated in Amazonia and Northeast Brazil (reaching up to 40%), and rainfall increases around the northern coast of Peru and Ecuador and in southeastern South America, reaching up to 30% in northern Argentina. All changes are more intense after 2040. The Precipitation–Evaporation (P–E) difference in the A1B downscaled scenario suggest water deficits and river runoff reductions in the eastern Amazon and São Francisco Basin, making these regions susceptible to drier conditions and droughts in the future.

Two Contrasting Severe Seasonal Extremes in Tropical South America in 2012: Flood in Amazonia and Drought in Northeast Brazil

AbstractTwo simultaneous extreme events affected tropical South America to the east of the Andes during the austral summer and fall of 2012: a severe drought in Northeast Brazil and intense rainfall and floods in Amazonia, both considered records for the last 50 years. Changes in atmospheric circulation and rainfall were consistent with the notion of an active role of colder-than-normal surface waters in the equatorial Pacific, with above-normal upward motion and rainfall in western Amazonia and increased subsidence over Northeast Brazil. Atmospheric circulation and soil moisture anomalies in the region contributed to an intensified transport of Atlantic moisture into the western part of Amazonia then turning southward to the southern Amazonia region, where the Chaco low was intensified. This was favored by the intensification of subtropical high pressure over the region, associated with an anomalously intense and northward-displaced Atlantic high over a relatively colder subtropical South Atlantic Ocean....

Extreme Seasonal Climate Variations in the Amazon Basin: Droughts and Floods

The last 10 years have featured intense climate-hydrological extremes in the Amazon region: 2005, 2009, 2010, 2012–2013, and 2014–2015 leading to great impacts, such as large-scale droughts and floods, some of them being classified as ‘once-in-a-century’ events. Historical records show previous droughts in 1926, 1964, 1980, 1983, and 1998 and floods in 1953, 1988, and 1989. These events have been linked to natural climate variability and they impact on natural and human systems. Main cities in the Amazon region were flooded or were isolated by the extremely low river levels during the droughts. Model projections suggest that such extremes could be more frequent/intense in the future and that human activities, mainly in the form of land use change leading to increases in greenhouse gas concentration, may aggravate such extremes and make the impacts on the populations stronger. In this chapter, we review climate-hydrological extremes in a historical context, assessing observed trends, projected climate change scenarios, and the likelihood and uncertainties inherent to those scenarios.

Assessment of Warming Projections and Probabilities for Brazil

This chapter considers four emission scenarios of CMIP5 simulations to analyze how greenhouse gases could evolve this century and to evaluate probabilities of additional warming to Brazil based on climate projections. The results are shown in values for average temperature and anomalies close to the surface. Thus, the probabilities for a range of different warming levels were obtained exceeding by 4 °C to 7 °C for RCP 8.5. In this scenario, Brazil shows a 100% probability of suffering temperature rises of over 4 °C before the end of this century. For more extreme warming as 7 °C, the probability is of 80% by 2200. The Brazil analysis serves two purposes: a) plausible adaptation strategies require local risk knowledge; and b) the focus on higher warming temperature changes is crucial for a cost-benefit analysis of mitigation policies to reduce the risks of impacts and damages caused by extreme regional climate change. Apparently small changes in the climate may have significant effects, especially if important thresholds are surpassed. Crops have little tolerance to high temperatures, and as the climate gets warmer, these limits may be exceeded more and more often. This is one of the reasons why temperatures rise of 4 °C or more might represent severe risks for global food safety and affect food-producing countries like Brazil.

Final Remarks and Recommendations

Studies related to climate change scenarios and their impacts in key sectors of the Brazil need to be addressed. Measures to address the climate change impacts identified in the Brazilian energy, water agriculture and biodiversity sectors need to be implemented. Risk assessments for these sectors, as well as others such as water resources, urban areas, sea level rise and natural disasters are essential to assist in understanding problems and threats consequence of a dangerous climate change due to warming about 4 °C, particularly in regions and sectors of Brazil that are already vulnerable to the extremes of climate variability. There is a need to minimize climate risks means influencing the developing of policies that prioritise the mitigation of emissions, as well as adaptation to future scenarios. Therefore, policy makers should address climate change as a risk management issue. As shown by this book, assessing the impacts of extreme climate events due to a warming above 4 °C on the energy, agricultural, health and biodiversity sectors is very complex.

Increase Risk of Drought in the Semiarid Lands of Northeast Brazil Due to Regional Warming above 4 °C

Although semiarid vegetation is usually resistant and highly resilient to water deficits, vegetation activity in semiarid region of Northeast Brazil (NEB) is highly controlled by interannual variations in water availability and decrease in water availability may trigger land degradation and desertification. Recurrent droughts conditions in semiarid regions, such as NEB, can produce a progressive loss of resilience that affects negatively vulnerable populations living from small-scale agriculture. The drought affecting this region continuously during the last 7 years shows an intensity and impact not seen in several decades in the regional economy and society, and represents an example oh what could happen in NEB in the future. In sum, regional warming above 4 °C is likely to increase the drought risk in Northeast Brazil, with increase temperature and decrease precipitation resulting in lower vegetal productivity and more unpredictable harvests. In municipalities, where smallholder livelihoods are not very diversified and are dominated by subsistence agriculture, even a moderate drought (as in 2012–13) can cause a decline in harvests; and, with an increased drought risk (as the future projections), the harvest scenario can still be worse and devastating for regional and national food security and economy. Therefore, there is an urgent need for proactive drought management and preparedness strategies as well as integrated assessments considering the synergy of impacts and limits to adaptation in multiple sectors and regions in a 4 °C warming for NEB.