Flood risk assessment of the Garita River in the urban zone of San Luis Potosí City, by hydrodynamic modeling.

Rapid and uncontrolled urban growth and land use changes in watersheds worldwide have led to increased surface runoff within metropolitan areas, coupled with climate change, creating a risk for residents during the rainy season. The city of San Luis Potosí is no exception to this phenomenon. One affected watercourse is the Garita Stream, which flows inside the city near urbanization. It is essential to analyze the effects of urban sprawl on this stream based on historical precipitation data for the town. Hydrological and topographical information were required to conduct this research. The hydrological study of the basin involved analyzing the region's geomorphology and historical climatological data. For the stream's topography, aerial photogrammetry using an unmanned aerial Vehicle (UAV) and Global Navigation Satellite System (GNSS) equipment was employed to conduct topographic surveys in the area. To find out when the Garita stream would overflow and which areas are most likely to flood, numerical modeling was done using 1D, 2D, and 3D programs like SWMM5 (Storm Water Management Model), HEC-RAS (Hydrologic Engineering Center's River Analysis System), and EDFC Explorer (Environmental Fluid Dynamics Code). These models simulated different return periods and their correlation with current flooding events recorded in the area, thereby further proposing solutions to mitigate overflow issues. By conducting these simulations and analyzing the results, solutions can be suggested to address the overflow problems in the area based on historical flood events at various return periods caused by the Garita Stream.

Exposure of protected areas in Central America to extreme weather events.

Central America and the Caribbean are regularly battered by megadroughts, heavy rainfall, heat waves, and tropical cyclones. Although 21st-century climate change is expected to increase the frequency, intensity, and duration of these extreme weather events (EWEs), their incidence in regional protected areas (PAs) remains poorly explored. We examined historical and projected EWEs across the region based on 32 metrics that describe distinct dimensions (i.e., intensity, duration, and frequency) of heat waves, cyclones, droughts, and rainfall and compared trends in PAs with trends in unprotected lands. From the early 21st century onward, exposure to EWEs increased across the region, and PAs were predicted to be more exposed to climate extremes than unprotected areas (as shown by autoregressive model coefficients at p < 0.05 significance level). This was particularly true for heat waves, which were projected to have a significantly higher average (tested by Wilcoxon tests at p < 0.01) intensity and duration, and tropical cyclones, which affected PAs more severely in carbon-intensive scenarios. PAs were also predicted to be significantly less exposed to droughts and heavy rainfall than unprotected areas (tested by Wilcoxon tests at p < 0.01). However, droughts that could threaten connectivity between PAs are increasingly common in this region. We estimated that approximately 65% of the study area will experience at least one drought episode that is more intense and longer lasting than previous droughts. Collectively, our results highlight that new conservation strategies adapted to threats associated with EWEs need to be tailored and implemented promptly. Unless urgent action is taken, significant damage may be inflicted on the unique biodiversity of the region.

Ciclones, olas de calor, sequías y lluvias intensas son eventos comunes en Centroamérica y el Caribe, cuya frecuencia, intensidad y duración se espera aumente durante el siglo XXI a causa del cambio climático. Sin embargo, en la actualidad, se desconoce cuál será la incidencia de estos eventos meteorológicos extremos (EME) dentro de las áreas protegidas. En este estudio examinamos la exposición histórica y futura a los extremos climáticos y comparamos el grado de exposición dentro y fuera de las áreas protegidas de toda la región por medio de 32 métricas que describen distintas dimensiones (intensidad, duración y frecuencia) de las olas de calor, los ciclones, las sequías y las precipitaciones. Los resultados indican que a medida que aumente el número de EME, las áreas protegidas estarán más expuestas a los extremos climáticos que las áreas no protegidas. Esto es especialmente cierto en el caso de las olas de calor, que, según las proyecciones, tendrán una intensidad y una duración medias significativamente mayores, y de los ciclones tropicales, que afectarán más gravemente a las zonas protegidas en los escenarios intensivos en carbono. Nuestros resultados también indican que las zonas protegidas estarán significativamente menos expuestas a sequías o lluvias torrenciales que las zonas no protegidas. Sin embargo, las sequías que podrían amenazar la conectividad entre áreas protegidas son cada vez más frecuentes en esta región. Se estima que aproximadamente el 65% del área de estudio experimentará al menos un episodio de sequía más intenso y duradero que las sequías anteriores. En conjunto, nuestros resultados ponen de relieve la necesidad de diseñar y aplicar con prontitud nuevas estrategias de conservación adaptadas a las amenazas asociadas a los EWE. A menos que se tomen medidas urgentes, la biodiversidad única de la región podría sufrir daños considerables.

Consumo alimentar da população urbana em um município da Amazônia Legal, nos eventos climáticos de inundação e seca: estudo comparativo / Food consumption of the urban population in a municipality in the Legal Amazon, during climate events of flood and drought: a comparative study / Consumo de alimentos en la población urbana en un municipio de la Amazonía Legal durante los eventos climáticos de inundación y sequía: un estudio comparativo

Resumo: O objetivo foi comparar o consumo alimentar da população de Coari, Amazonas, Brasil, segundo a Classificação NOVA, durante as fases hidrológicas de seca e inundação dos rios amazônicos. Realizou-se um estudo epidemiológico, de base populacional e transversal. A amostra foi composta por 457 indivíduos adultos e a coleta de dados foi realizada em dois momentos, mediante um instrumento sociodemográfico, um recordatório alimentar de 24 horas, e um questionário de frequência alimentar adaptado para os hábitos locais. Os dados foram analisados pelo programa estatístico R versão 4.2.4, por meio dos testes qui-quadrado de Pearson, exato de Fischer e de Bhapkar. A amostra foi composta predominantemente pelo sexo feminino (seca = 70%/inundação = 71,2%) e pardos (seca = 65,4%/inundação = 66,2%). As refeições (café da manhã, almoço e jantar) foram realizadas pela maior parte dos entrevistados. O lanche da tarde foi a refeição intermediária mais realizada, principalmente na inundação (274/70,2%). Predominou-se o consumo de alimentos in natura ou minimamente processados nas três principais refeições (95%). Os ultraprocessados são pouco ou não são consumidos e foram citados especialmente na seca (152/33,3%; p = 0,007). Em contrapartida, o consumo de alimentos regionais (tucumã, beiju, farinha de tapioca e açaí) aumentou durante a inundação (p < 0,001). O consumo de alimentos in natura ou minimamente processados continua sendo a base da alimentação no interior do Amazonas, predominando alimentos regionais na inundação e alimentos processados e ultraprocessados na seca, demonstrando a influência, ainda que sutil, das fases hidrológicas no consumo alimentar dessa população.

Abstract: The aim of this study was to compare the food consumption of the population of Coari, Amazonas State, Brazil, according to the NOVA Classification, during the hydrological phases of drought and flooding of the Amazon rivers. An epidemiological, population-based, cross-sectional study was carried out. The sample consisted of 457 adult individuals. Data were collected in two stages using a sociodemographic instrument, a 24-hour food recall and a food frequency questionnaire adapted to local habits. The data were analyzed using the statistical program R version 4.2.4, using Pearson's chi-square, Fischer's exact and Bhapkar's tests. The sample was predominantly female (drought = 70%/flood = 71.2%) and brown (drought = 65.4%/flood = 66.2%). Most of the interviewees ate meals (breakfast, lunch and dinner). Afternoon snacks were the most common intermediate meal, especially during flooding (274/70.2%). In natura or minimally processed foods predominated at the three main meals (95%). Ultra-processed foods were consumed little or not at all and were mentioned especially during the drought (152/33.3%; p = 0.007). On the other hand, consumption of regional foods (tucumã, beiju, tapioca flour and açaí) increased during the flood (p < 0.001). Consumption of in natura or minimally processed foods continues to be the mainstay of the diet in the interior of Amazonas, with a predominance of regional foods during the flood and processed and ultra-processed foods during the drought, demonstrating the influence, albeit subtle, of the hydrological phases on the food consumption of this population.

Resumen: El objetivo de este estudio fue comparar el consumo de alimentos de la población de Coari, Amazonas, Brasil, según la Clasificación NOVA, durante las fases hidrológicas de sequía e inundación de los ríos amazónicos. Se trató de un estudio epidemiológico, poblacional y transversal. La muestra estuvo conformada por 457 individuos adultos. Los datos se recogieron en dos etapas mediante un instrumento sociodemográfico, un recordatorio de alimentos las 24 horas, y un cuestionario de frecuencia alimentar adaptado a las costumbres locales. Para el análisis de datos se utilizó el programa estadístico R versión 4.2.4, mediante las pruebas chi-cuadrado de Pearson, exacto de Fisher y de Bhapkar. Hubo un mayor predominio del sexo femenino (sequía = 70%/inundación = 71,2%) y de pardos (sequía = 65,4%/inundación = 66,2%). La mayoría de los entrevistados tuvieron sus comidas (desayuno, almuerzo y cena) en el período analizado. La merienda fue la comida intermedia más frecuente, especialmente en la inundación (274/70,2%). El consumo de alimentos in natura o mínimamente procesados predominó en las tres comidas principales (95%). Los productos ultraprocesados fueron poco o nada consumidos y se los mencionaron especialmente en la sequía (152/33,3%; p = 0,007). Por otro lado, el consumo de alimentos regionales (tucumã, beiju, harina de tapioca y açaí) tuvo un aumento durante la inundación (p < 0,001). El consumo de alimentos in natura o mínimamente procesados sigue siendo la base alimentar en el interior de la Amazonía, con predominio en el consumo de alimentos regionales en la inundación y de alimentos procesados y ultraprocesados en la sequía, lo que evidencia la influencia, aunque discreta, de las fases hidrológicas en el consumo de alimentos de esta población.

The economics impacts of long-run droughts: Challenges, gaps, and way forward.

Quantifying drought's economic impacts has been key for decision-making to build future strategies and improve the development and implementation of proactive plans. However, climate change is changing drought frequency, intensity, and durability. These changes imply modifications of their economic impact, as longer droughts result in greater cumulative economic losses for water users. Though the longer the drought lasts, other factors also play a crucial role in its economic outcomes, such as Infrastructure capacity (IC), the Amount of Water in Storage (AWS) in reservoirs and aquifers, and short- and long-term responses to it. This study proposes and applies an analytical framework for the economic assessment of long-run droughts, assessing and explaining central Chile megadrought economic effects through the factors that begin to influence the economic impact level in this setting. High levels of both IC and the AWS, as well as short- and long-term responses of water users, allow for high resilience to long-run droughts, tolerating extraordinary water disruption in its society with relatively low total economic impacts. Despite this adaptability, long-term droughts bring places to a water-critical threshold where long-term adaptation strategies may be less flexible than short-term strategies, escalating the adverse economic effects. This fact suggests that the economic evaluation of megadrought needs to focus on future tipping points (substantial water scarcity). The tipping point depends on the IC, how water users manage the AWS, and adaptation strategies. Establishing the tipping point should be a priority for future interdisciplinary research.

A comprehensive resilience assessment of Mexican tree species and their relationship with drought events over the last century.

The resilience of forests to drought events has become a major natural resource sustainability concern, especially in response to climate change. Yet, little is known about the legacy effects of repeated droughts, and tree species ability to respond across environmental gradients. In this study, we used a tree-ring database (121 sites) to evaluate the overall resilience of tree species to drought events in the last century. We investigated how climate and geography affected the response at the species level. We evaluated temporal trends of resilience using a predictive mixed linear modeling approach. We found that pointer years (e.g., tree growth reduction) occurred during 11.3% of the 20th century, with an average decrease in tree growth of 66% compared to the previous period. The occurrence of pointer years was associated with negative values of the Standardized Precipitation Index (SPI, 81.6%) and Palmer Drought Severity Index (PDSI, 77.3%). Tree species differed in their resilience capacity, however, species inhabiting xeric conditions were less resistant but with higher recovery rates (e.g., Abies concolor, Pinus lambertiana, and Pinus jeffreyi). On average, tree species needed 2.7 years to recover from drought events, with extreme cases requiring more than a decade to reach pre-drought tree growth rates. The main abiotic factor related to resilience was precipitation, confirming that some tree species are better adapted to resist the effects of droughts. We found a temporal variation for all tree resilience indices (scaled to 100), with a decreasing resistance (-0.56 by decade) and resilience (-0.22 by decade), but with a higher recovery (+1.72 by decade) and relative resilience rate (+0.33 by decade). Our results emphasize the importance of time series of forest resilience, particularly by distinguishing the species-level response in the context of legacy of droughts, which are likely to become more frequent and intense under a changing climate.

Drought-heatwave nexus in Brazil and related impacts on health and fires: A comprehensive review.

Climate change is drastically altering the frequency, duration, and severity of compound drought-heatwave (CDHW) episodes, which present a new challenge in environmental and socioeconomic sectors. These threats are of particular importance in low-income regions with growing populations, fragile infrastructure, and threatened ecosystems. This review synthesizes emerging progress in the understanding of CDHW patterns in Brazil while providing insights about the impacts on fire occurrence and public health. Evidence is mounting that heatwaves are becoming increasingly linked with droughts in northeastern and southeastern Brazil, the Amazonia, and the Pantanal. In those regions, recent studies have begun to build a better understanding of the physical mechanisms behind CDHW events, such as the soil moisture-atmosphere coupling, promoted by exceptional atmospheric blocking conditions. Results hint at a synergy between CDHW events and high fire activity in the country over the last decades, with the most recent example being the catastrophic 2020 fires in the Pantanal. Moreover, we show that HWs were responsible for increasing mortality and preterm births during record-breaking droughts in southeastern Brazil. This work paves the way for a more in-depth understanding on CDHW events and their impacts, which is crucial to enhance the adaptive capacity of different Brazilian sectors.

Burning in southwestern Brazilian Amazonia, 2016-2019.

Fire is one of the most powerful modifiers of the Amazonian landscape and knowledge about its drivers is needed for planning control and suppression. A plethora of factors may play a role in the annual dynamics of fire frequency, spanning the biophysical, climatic, socioeconomic and institutional dimensions. To uncover the main forces currently at play, we investigated the area burned in both forested and deforested areas in the outstanding case of Brazil's state of Acre, in southwestern Amazonia. We mapped burn scars in already-deforested areas and intact forest based on satellite images from the Landsat series analyzed between 2016 and 2019. The mapped burnings in already-deforested areas totalled 550,251 ha. In addition, we mapped three forest fires totaling 34,084 ha. Fire and deforestation were highly correlated, and the latter occurred mainly in federal government lands, with protected areas showing unprecedented forest fire levels in 2019. These results indicate that Acre state is under increased fire risk even during average rainfall years. The record fires of 2019 may continue if Brazil's ongoing softening of environmental regulations and enforcement is maintained. Acre and other Amazonian states must act quickly to avoid an upsurge of social and economic losses in the coming years.

Monitoring air temperature for the thermal comfort and conservation of forests / Monitoramento da temperatura atmosférica visando o conforto térmico e a conservação de florestas

As ondas de calor têm despertado a preocupação quanto aos danos que ocasionam sobre os serviços ecossistêmicos, e combinadas com estiagens, o excesso de calor tem favorecido o aumento da mortalidade das árvores mundo afora. Partindo-se da hipótese em que a região sudoeste do Paraná, apresenta condições favoráveis à ocorrência de anomalias climáticas caracterizadas como ondas de calorde verão, este trabalho teve como objetivo geral, observar o comportamento da temperatura atmosférica no município de Dois Vizinhos, para o interstício entre 2018 a 2020, e em específico: i) analisar quais os intervalos dos horários de verão em Dois Vizinhos, a temperatura atmosférica se apresenta mais elevada;ii) verificar por meio do índice proposto de estresse florestal (forest-based stress index ou FBS), os eventos caracterizados como de onda de calor, entre os anos de 2018 a 2020; iii) discutir a viabilidade do índice FBS, tendo como critério, outros índices de monitoramento ambiental; iv) apresentar argumentos sobre aspectos ecofisiológicos e de conservação florestal. As conclusões foram que o período noturno entre 21h-03h de 2020, da estação de verão de Dois Vizinhos, foi significativamente mais quente, no triênio analisado. O horário entre 15h-21h de 2020 foi significativamente mais quente, entre as categorias horarias analisadas. Por meio do índice FBS de estresse florestal, verificou-se o total de 36 episódios caracterizados como de Ondas de Calor na localidade, inclusive noturnas, entre os anos de 2018 a 2020.

Heat waves have raised concerns about the damage they do to ecosystem services, and combined with droughts, excessive heat has favored the rise in tree mortality worldwide. Based on the hypothesis that the southwestern region of the state of Paraná presents suitable conditions for the occurrence of anomalousweather events characterized as summer heat waves, this study was conducted to observe air temperature patterns in the municipality of Dois Vizinhos between 2018 and 2020. Its specific objectives were to i) determine which periods of the day during the summer in Dois Vizinhos registered the highest air temperatures; ii) verify the events characterized as heat waves between the years 2018 and 2020 using the proposed forest-based stress index (FBS); iii) discuss the feasibility of the FBS index by making reference to other environmental monitoring indices; and iv) present arguments on aspects of ecophysiology and forest conservation. The results showed that the night period between 9 p.m. and 3 a.m. in Dois Vizinhos in summer 2020 was significantly hotter in the three years of the study. The interval between 3 p.m. and 9 p.m. in summer 2020 was significantly hotter among the hourly categories recorded. According to the FBS index, there were a total of 36 episodes characterized as Heat Waves in this region,including the nighttime.

Monitoring air temperature for the thermal comfort and conservation of forests / Monitoramento da temperatura atmosférica visando o conforto térmico e a conservação de florestas

As ondas de calor têm despertado a preocupação quanto aos danos que ocasionam sobre os serviços ecossistêmicos, e combinadas com estiagens, o excesso de calor tem favorecido o aumento da mortalidade das árvores mundo afora. Partindo-se da hipótese em que a região sudoeste do Paraná, apresenta condições favoráveis à ocorrência de anomalias climáticas caracterizadas como ondas de calorde verão, este trabalho teve como objetivo geral, observar o comportamento da temperatura atmosférica no município de Dois Vizinhos, para o interstício entre 2018 a 2020, e em específico: i) analisar quais os intervalos dos horários de verão em Dois Vizinhos, a temperatura atmosférica se apresenta mais elevada;ii) verificar por meio do índice proposto de estresse florestal (forest-based stress index ou FBS), os eventos caracterizados como de onda de calor, entre os anos de 2018 a 2020; iii) discutir a viabilidade do índice FBS, tendo como critério, outros índices de monitoramento ambiental; iv) apresentar argumentos sobre aspectos ecofisiológicos e de conservação florestal. As conclusões foram que o período noturno entre 21h-03h de 2020, da estação de verão de Dois Vizinhos, foi significativamente mais quente, no triênio analisado. O horário entre 15h-21h de 2020 foi significativamente mais quente, entre as categorias horarias analisadas. Por meio do índice FBS de estresse florestal, verificou-se o total de 36 episódios caracterizados como de Ondas de Calor na localidade, inclusive noturnas, entre os anos de 2018 a 2020.(AU)

Heat waves have raised concerns about the damage they do to ecosystem services, and combined with droughts, excessive heat has favored the rise in tree mortality worldwide. Based on the hypothesis that the southwestern region of the state of Paraná presents suitable conditions for the occurrence of anomalousweather events characterized as summer heat waves, this study was conducted to observe air temperature patterns in the municipality of Dois Vizinhos between 2018 and 2020. Its specific objectives were to i) determine which periods of the day during the summer in Dois Vizinhos registered the highest air temperatures; ii) verify the events characterized as heat waves between the years 2018 and 2020 using the proposed forest-based stress index (FBS); iii) discuss the feasibility of the FBS index by making reference to other environmental monitoring indices; and iv) present arguments on aspects of ecophysiology and forest conservation. The results showed that the night period between 9 p.m. and 3 a.m. in Dois Vizinhos in summer 2020 was significantly hotter in the three years of the study. The interval between 3 p.m. and 9 p.m. in summer 2020 was significantly hotter among the hourly categories recorded. According to the FBS index, there were a total of 36 episodes characterized as Heat Waves in this region,including the nighttime.(AU)

Variações da qualidade da água de chuva e de açudes armazenada em cisternas em municípios do semiárido do estado da Paraíba / Variations in the quality of rainwater and fluvial reservoirs stored in cisterns in municipalities of the semiarid region of Paraíba State

RESUMO Neste trabalho são apresentadas a evolução temporal de parâmetros de qualidade e a análise de conformidade da água armazenada em cisternas nos municípios de Barra de Santana, Boqueirão e Caturité, no semiárido do estado da Paraíba. A água armazenada nas cisternas estudadas é oriunda da chuva e dos açudes Epitácio Pessoa, na região do Cariri, e Araçagi, na região do Brejo. Foram analisados os valores dos parâmetros pH, turbidez, condutividade elétrica, sólidos totais dissolvidos, alcalinidade total, cor aparente, dureza total, cloretos, amônia, sulfato, nitrato, coliformes totais, coliformes termotolerantes, Escherichia coli e bactérias heterotróficas, com frequência mensal nos meses de fevereiro a outubro de 2017, em plena seca de 2011/2017. Foram observadas variações relevantes nos parâmetros da água oriunda dos açudes, principalmente do açude Epitácio Pessoa, em decorrência do aporte de água do rio São Francisco por meio do Projeto de Integração do Rio São Francisco com as Bacias do Nordeste Setentrional (PISF). Os resultados indicaram que não houve variações consideráveis nos parâmetros da água de chuva armazenada nas cisternas. Diferentemente das cisternas com águas de açudes, houve conformidade em relação à Portaria nº 5/2017 do Ministério da Saúde para todos os parâmetros físicos e químicos analisados nas cisternas com água de chuva.

Abstract In this work, the temporal evolution of quality parameters and the analysis of the conformity of water stored in cisterns in the municipalities of Barra de Santana, Boqueirão, and Caturité in the semi-arid state of Paraíba are presented. The water stored in the cisterns studied comes from rain and from Epitácio Pessoa fluvial reservoirs in the region of Cariri and Araçagi in the region of Brejo. The parameters analyzed were: pH, turbidity, electrical conductivity, total dissolved solids, total alkalinity, apparent color, total hardness, chlorides, ammonia, sulfate, nitrate, total coliforms, thermotolerant coliforms, Escherichia coli, and heterotrophic bacteria, with monthly frequency in the months of February to October 2017, in the midst of the 2011/2017 drought. Relevant variations were observed in the parameters of the water coming from fluvial reservoirs, mainly from Epitácio Pessoa due to the water supply of the São Francisco river through the São Francisco River Integration Project (Projeto de Integração do Rio São Francisco - PISF). The results indicated that there were no significant changes in rainwater storage parameters in cisterns. Unlike cisterns with water from fluvial reservoirs, there was compliance in relation to Ordinance No. 5/2017 of the Ministry of Health for all the physical and chemical parameters analyzed in cisterns with rainwater.

Reconstrucción histórica de la precipitación en la Reserva de la Biosfera El Cielo, México, mediante anillos de crecimiento en Taxodium mucronatum (Cupressaceae) / Historical precipitation reconstruction of El Cielo Biosphere Reserve, Mexico, using Taxodium mucronatum (Cupressaceae) annual growth rings

Introducción: El conocimiento histórico del clima es fundamental para analizar su variabilidad en el tiempo y su impacto en los ecosistemas y poblaciones humanas. Objetivo: Analizar el crecimiento anual de los árboles de sabino, también conocido como ahuehuete (Taxodium mucronatum) del río Sabinas para reconstruir la variabilidad de precipitación histórica en la Reserva de la Biosfera El Cielo, Tamaulipas, México. Métodos: Se fecharon los crecimientos anuales de 116 muestras de sabino, a partir de las cuales se desarrolló una cronología de 544 años (1474-2017). El periodo que sustentó un número de muestras adecuado para el análisis climático se extiende de 1550 a 2017 (468 años). Resultados: Con base en el análisis de función respuesta se determinó que la precipitación de invierno-primavera (noviembre-mayo) influyó de manera significativa en el crecimiento de los sabinos en el área de estudio (r= 0.77, P < 0.001). La reconstrucción registró una variabilidad climática alta a nivel interanual y entre décadas, en la cual, se identificó la presencia de sequías a principios y finales de cada siglo, así como la presencia de sequías extremas cíclicas cada 50 años. Estas sequías destacaron por su impacto social y económico a nivel nacional y regional. Las sequías más importantes son el "Año Uno Conejo" de acuerdo con el calendario Azteca, en 1558; la sequía de1696 con un impacto fuerte en el noreste de México; "El Año del Hambre" en 1785-1786, en la Reserva de la Biosfera El Cielo desde 1784; la sequía de 1801 que trajo consigo la escasez de alimentos; la de 1951 dentro del periodo de "Migración masiva del sector rural"; y la sequía más reciente, registrada en 2011. Las lluvias extremas más representativas sucedieron en 1756 y 1816. Conclusiones: De seguir el patrón de precipitación registrado en la Reserva de la Biosfera El Cielo, es posible esperar la presencia de sequías extremas a mediados y finales del siglo XXI.

Introduction: Historical knowledge of climate is essential to analyze its variability over time, as well as its impact on natural ecosystems and human populations. Objective: To analyze the annual growth of the sabino trees, also known as ahuehuete trees (Taxodium mucronatum) from the Sabinas River to reconstruct the historical variability of precipitation in El Cielo Biosphere Reserve, Tamaulipas, Mexico. Methods: The annual growth of 116 sabino samples was dated to develop a chronology of 544 years (1474-2017). The period that admitted a series of samples suitable for climate analysis extends from 1550 to 2017 (468 years). Results: Based on the analysis of the response function, it was determined that the winter-spring precipitation (November-May) significantly influenced the radial growth of sabinos in the study area (R= 0.77, P < 0.001). The reconstruction recorded high climatic variability at interannual and interdecadal levels, in which the presence of droughts was identified at the beginning and end of each century, as well as the presence of extreme cyclical droughts every 50 years. These droughts stood out for their social and economic impact at the regional and national level. The most important droughts are the "Año Uno Conejo" ("Year One Rabbit") according to the Aztec calendar in 1558. In 1696 with a strong impact in Northern Mexico. "El Año del Hambre" ("The Year of Hunger") in 1785-1786. Also, the drought of 1801 that brought alongside food shortages. 1951 within the period of "Mass migration of the rural sector"; and the most recent drought, recorded in 2011. The most representative extreme rainfalls occurred in 1756 and 1816. Conclusions: If the precipitation pattern registered at El Cielo Biosphere Reserve continues, it is possible to expect the presence of extreme droughts in the mid and late 21st century.

Ecosystem heterogeneity and diversity mitigate Amazon forest resilience to frequent extreme droughts.

The impact of increases in drought frequency on the Amazon forest's composition, structure and functioning remain uncertain. We used a process- and individual-based ecosystem model (ED2) to quantify the forest's vulnerability to increased drought recurrence. We generated meteorologically realistic, drier-than-observed rainfall scenarios for two Amazon forest sites, Paracou (wetter) and Tapajós (drier), to evaluate the impacts of more frequent droughts on forest biomass, structure and composition. The wet site was insensitive to the tested scenarios, whereas at the dry site biomass declined when average rainfall reduction exceeded 15%, due to high mortality of large-sized evergreen trees. Biomass losses persisted when year-long drought recurrence was shorter than 2-7 yr, depending upon soil texture and leaf phenology. From the site-level scenario results, we developed regionally applicable metrics to quantify the Amazon forest's climatological proximity to rainfall regimes likely to cause biomass loss > 20% in 50 yr according to ED2 predictions. Nearly 25% (1.8 million km2 ) of the Amazon forests could experience frequent droughts and biomass loss if mean annual rainfall or interannual variability changed by 2σ. At least 10% of the high-emission climate projections (CMIP5/RCP8.5 models) predict critically dry regimes over 25% of the Amazon forest area by 2100.