Regina Célia dos Santos Alvalá

Climatic characteristics of the 2010-2016 drought in the semiarid Northeast Brazil region

This study discusses the climatological aspects of the most severe drought ever recorded in the semiarid region Northeast Brazil. Droughts are recurrent in the region and while El Nino has driven some of these events others are more dependent on the tropical North Atlantic sea surface temperature fields. The drought affecting this region during the last 5 years shows an intensity and impact not seen in several decades in the regional economy and society. The analysis of this event using drought indicators as well as meteorological fields shows that since the middle 1990s to 2016, 16 out of 25 years experienced rainfall below normal. This suggests that the recent drought may have in fact started in the middle-late 1990s, with the intense droughts of 1993 and 1998, and then the sequence of dry years (interrupted by relatively wet years in 2007, 2008, 2009 and 2011) after that may have affected the levels of reservoirs in the region, leading to a real water crisis that was magnified by the negative rainfall anomalies since 2010.

Relação do padrão sazonal da vegetação com a precipitação na região de cerrado da Amazônia Legal, usando índices espectrais de vegetação

A precipitacao e um dos principais fatores que determina a dinâmica sazonal da vegetacao na regiao de savanas tropicais, como e o caso do cerrado brasileiro. Neste trabalho foram analisadas as relacoes da precipitacao sazonal, com o comportamento sazonal das classes de uso e cobertura da terra (UCT), principalmente as fisionomias de cerrado do Estado de Tocantins. Foi analisada a dinâmica sazonal do cerrado, incluindo areas florestadas e nao florestadas, a partir da analise de imagens do MODIS/TERRA IV (Indices de Vegetacao) de janeiro a dezembro de 2004, bem como dados diarios de precipitacao de 2004 e uma serie de precipitacao diaria do periodo de 1969 a 2005. Os resultados da analise de precipitacao mostram que a area de estudo apresentou uma alta sazonalidade, com estacao seca de maio a setembro. As analises dos IV mostram que a dinâmica sazonal das formacoes de cerrado e similar aquela das areas convertidas para outros usos. O padrao sazonal das classes de UCT segue os padroes da precipitacao, cujos menores valores foram registrados no mes de agosto de 2004, mes este que apresentou os menores valores dos IV. Diferentemente das demais classes de UCT, a formacao florestal nao se ajustou ao padrao de precipitacao, apresentando valores de IV similares ao longo do ano com leve decrescimo no mes de setembro de 2004.

Impactos das mudanças de cobertura vegetal nos processos de superfície na região semiárida do Brasil

Vegetation cover on the surface of the Earth has changed considerably due to human activities, mainly through the conversion of natural vegetation to croplands and pastures. These changes have altered regional and global climates through biophysical and biogeochemical processes. In this work, the effects of the conversion of natural caatinga to croplands and to degraded caatinga on the land surface processes in the semiarid region of Brazil are analysed using the Integrated Biosphere Simulator (IBIS) model. Through these land cover changes, the biophysical and morphological characteristics of the vegetation have been modified and therefore, these changes have affected the exchange of energy, water and carbon between the atmosphere and land surface. Results of a simulated conversion from caatinga cover to cropland and degraded caatinga show that surface albedo (in wet and dry season) increased, consequently the energy balance was altered. In addition, roughness length and stomatal conductance changes corroborate the variations in turbulent exchanges between the surface and atmosphere. Regarding the components of carbon balance, when caatinga is replaced by cropland, the net ecosystem exchange (NEE) and net primary productivity (NPP) increases. The opposite effects are found when caatinga is replaced by degraded caatinga. It indicates that the metabolic activity of the ecosystem decreases and this land cover (degraded caatinga) is acting as a source of CO2 to the atmosphere, however with low rates. The present work has important implications for land use management issues in the semiarid region of Brazil, including efforts to restore and preserve the natural ecosystem.

Calibration and Validation of the Integrated Biosphere Simulator (IBIS) for a Brazilian Semiarid Region

AbstractThe reliability of predictions from climate and weather models is linked to an adequate representation of the land surface processes. To evaluate performance and to improve predictions, land surface models are calibrated against observed data. Despite an extensive literature describing methods of land surface model calibration, few studies have applied a calibration method for semiarid natural vegetation, especially for the semiarid northeast of Brazil, which presents caatinga as its natural vegetation. Caatinga is a highly dynamic ecosystem with the physics at the land surface–atmosphere interface still poorly understood. Therefore, in this study a multiobjective hierarchical method, which provides means to estimate optimal values of the model parameters through calibration, is evaluated. This method is applied to caatinga by using the Integrated Biosphere Simulator (IBIS). Results demonstrated that the calibrated set of vegetation parameters produced a considerably different energy balance from ...

BALANÇO DE RADIAÇÃO NO PANTANAL SUL MATO-GROSSENSE DURANTE A ESTAÇÃO SECA

Este trabalho apresenta a analise das componentes do balanco de radiacao a superficie sobre o Pantanal Sul Mato-grossense, a partir de medidas experimentais coletadas durante a estacao seca, em setembro de 1999. Neste periodo, as componentes do balanco de radiacao mostraram um ciclo diurno bem definido, associado a densidade de fluxo radiativo de onda curta de 850 Wm-2 ao meio dia. O albedo medio apresentou um comportamento quase especular, com valor minimo de 0,16±0,02 para ângulos zenitais pequenos. Os valores de emissividade da superficie pantaneira, corrigida para temperatura radiativa de um corpo cinza, variaram entre 0,94 e 0,96. A partir das medidas diretas das densidades dos fluxos radiativos de ondas curtas e longas atmosfericas determinou-se os parâmetros otimos empregados nas formulacoes propostas por Monteith e Unsworth (2008), Swinbank (1963) e Brutsaert (1975).

Calibration of the “Simplified Simple Biosphere Model—SSiB” for the Brazilian Northeast Caatinga

The Brazilian Northeast region is covered largely by vegetation adapted to the arid conditions and with varied physiognomy, called caatinga. It occupies an extension of about 800.000 km2 that corresponds to 70% of the region. In recent decades, considerable progress in understanding the micrometeorological processes has been reached, with results that were incorporated into soil‐vegetation‐atmosphere transfer schemes (SVATS) to study the momentum, energy, water vapor, carbon cycle and vegetation dynamics changes of different ecosystems. Notwithstanding, the knowledge of the parameters and physical or physiological characteristics of the vegetation and soil of the caatinga region is very scarce. So, the objective of this work was performing a calibration of the parameters of the SSiB model for the Brazilian Northeast Caatinga. Micrometeorological and hydrological data collected from July 2004 to June 2005, obtained in the Agricultural Research Center of the Semi‐Arid Tropic (CPATSA), were used. Preceding t...

Impact of Soil Moisture on Crop Yields over Brazilian Semiarid

The objective of this work was to investigate the relationship between soil water content and rainfall with rice, beans, cassava and corn yields of in the semiarid region of Northeast Brazil. Precipitation and modeled soil water content were compared to yields recorded at the county levels in this region. The results were also integrated over the area of the nine States that lie within the officially recognized region of semiarid climate in Brazil. The influence of water balance components was quantified by calculating their correlation coefficient with yields of the different crop species over the municipalities of the region. It was found that rainfall had higher correlation to crop yields over most of the region, while soil water content had lower values of correlation. This result is consistent with the fact that average root depth is 40 cm, lower than the layer of soil used in the model used to estimate soil water content (100 cm). Plants respond better to the precipitation in the top layers of soil, while the water storage in the deep layer of soil might be important only in other temporal and spatial scales of the hydrological cycle. It is concluded that the average crop yield is directly associated with practices that increase soil moisture at the depth of the root system in order to reduce the effects caused by drought.

Influência do Crescimento Urbano sobre o Microclima de Manaus e Belém: Um Estudo Observacional (The influence of urban growth on the microclimate of Manaus and Belém: A observational study)

O crescimento urbano, relacionado com acelerados processos de urbanizacao e consequentes mudancas dos usos e cobertura da terra podem modificar diretamente o balanco de energia em superficie, gerando modificacoes na atmosfera que podem variar em escalas local ate regional. Procurando entender as dimensoes dos efeitos da urbanizacao em cidades da regiao Norte do Brasil, o principal objetivo deste trabalho e estudar a influencia do crescimento urbano sobre o microclima local das cidades de Manaus e Belem. Para o estudo foram utilizadas series historicas de temperatura e precipitacao coletados nos dois municipios, assim como imagens de satelite e dados de reanalises atmosfericas. Os resultados obtidos atraves das analises de tendencias mostraram uma elevacao na temperatura de ate 1,5 oC nos ultimos 50 anos, diretamente associada com o crescimento da area urbana. Analises de extremos de temperatura diaria tambem apontaram que o microclima das cidades de Manaus e Belem esta modificando, sendo influenciado nao so pela variabilidade climatica, mas tambem por mudancas nos usos da terra relacionados com processos de urbanizacao. A partir dos resultados foi possivel observar que o crescimento da area urbana e aumento da populacao apresentam relacao direta com modificacoes no microclima local das duas cidades. A B S T R A C T The urban growth associated with the urbanization process can directly modify the surface energy balance, generating changes in the atmosphere that may vary from the local to regional scale. Thus, trying to understand the dimensions of the effects of urbanization, the objective of this work is to study the influence of urban growth on the local microclimate of the cities of Manaus and Belem. For the study we used historical temperature and rainfall data collected in both cities, as well as satellite imagery and atmospheric reanalysis data. The results obtained through trend analysis showed an increase of temperature of up to 1.5 o C in the last 50 years, showing a possible relationship with the urban growth. Analysis of extreme daily temperature also proved that the microclimate of Manaus and Belem is changing, being influenced not only by climate variability, but also by changes in land-related processes, such as urbanization. In the results we observed that the growth of the urban area and the increase of population is directly related to changes in local microclimate of the cities. Keywords: Urbanization, Amazon, Temperature trends

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.

Use of SMOS L3 Soil Moisture Data: Validation and Drought Assessment for Pernambuco State, Northeast Brazil

The goal of this study was to validate soil moisture data from Soil Moisture Ocean Salinity (SMOS) using two in situ databases for Pernambuco State, located in Northeast Brazil. The validation process involved two approaches, pixel-station comparison and areal average, for three regions in Pernambuco with different climatic characteristics. After validation, the SMOS data were used for drought assessment by calculating soil moisture anomalies for the available period of data. Four statistical criteria were used to verify the quality of the satellite data: Pearson correlation coefficient, Willmott index of agreement, BIAS, and root mean squared difference (RMSD). The average RMSD calculated from the daily time series in the pixel and the areal assessment were 0.071 m3m-3 and 0.04 m3m-3, respectively. Those values are near to the expected 0.04 m3m-3 accuracy of the SMOS mission. The analysis of soil moisture anomalies enabled the assessment of the dry period between 2012 and 2017 and the identification of regions most impacted by the drought. The driest year for all regions was 2012, when the anomaly values achieved -50% in some regions. The use of SMOS data provided additional information that was used in conjunction with the precipitation data to assess drought periods. This may be particularly relevant for planning in agriculture and supporting decision makers and farmers.