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1. Increased mortality of tropical tree seedlings during the extreme 2015–16 El Niño

   https://doi.org/10.1111/gcb.15809  

   Browne, Luke; Markesteijn, Lars; Engelbrecht, Bettina M. J.; Jones, F. Andrew; Lewis, Owen T.; Manzané‐Pinzón, Eric; Wright, S. Joseph; Comita, Liza S. (July 2021, Global Change Biology)

   Abstract As extreme climate events are predicted to become more frequent because of global climate change, understanding their impacts on natural systems is crucial. Tropical forests are vulnerable to droughts associated with extreme El Niño events. However, little is known about how tropical seedling communities respond to El Niño–related droughts, even though patterns of seedling survival shape future forest structure and diversity. Using long‐term data from eight tropical moist forests spanning a rainfall gradient in central Panama, we show that community‐wide seedling mortality increased by 11% during the extreme 2015–16 El Niño, with mortality increasing most in drought‐sensitive species and in wetter forests. These results indicate that severe El Niño–related droughts influence understory dynamics in tropical forests, with effects varying both within and across sites. Our findings suggest that predicted increases in the frequency of extreme El Niño events will alter tropical plant communities through their effects on early life stages. 

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2. Drought and Flood Extremes on the Amazon River and in Northeast Brazil, 1790–1900

   https://doi.org/10.1175/JCLI-D-23-0146.1  

   Granato-Souza, Daniela; Stahle, David W. (October 2023, Journal of Climate)

   Abstract Recent severe droughts, extreme floods, and increasing differences between seasonal high and low flows on the Amazon River may represent a twenty-first-century increase in the amplitude of the hydrologic cycle over the Amazon Basin. These precipitation and streamflow changes may have arisen from natural ocean–atmospheric variability, deforestation within the drainage basin of the Amazon River, or anthropogenic climate change. Tree-ring reconstructions of wet-season precipitation extremes, substantiated with historical accounts of climate and river levels on the Amazon River and in northeast Brazil found in the Brazilian Digital Library, indicate that the recent river-level extremes on the Amazon may have been equaled or possibly exceeded during the preinstrumental nineteenth century. The “Forgotten Drought” of 1865 was the lowest wet-season rainfall total reconstructed with tree-rings in the eastern Amazon from 1790 to 2016 and appears to have been one of the lowest stream levels observed on the Amazon River during the historical era according to first-hand descriptions by Louis Agassiz, his Brazilian colleague João Martins da Silva Coutinho, and others. Heavy rains and flooding are described during most of the tree-ring-reconstructed wet extremes, including the complete inundation of “First Street” in Santarem, Brazil, in 1859 and the overtopping of the Bittencourt Bridge in Manaus, Brazil, in 1892. These extremes in the tree-ring estimates and historical observations indicate that recent high and low flow anomalies on the Amazon River may not have exceeded the natural variability of precipitation and streamflow during the nineteenth century. Significance StatementProxy tree-ring and historical evidence for precipitation extremes during the preinstrumental nineteenth century indicate that recent floods and droughts on the Amazon River may have not yet exceeded the range of natural hydroclimatic variability. 

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3. Cross-Site Comparisons of Dryland Ecosystem Response to Climate Change in the US Long-Term Ecological Research Network

   https://doi.org/10.1093/biosci/biab134  

   Hudson, Amy R.; Peters, Debra P. C.; Blair, John M.; Childers, Daniel L.; Doran, Peter T.; Geil, Kerrie; Gooseff, Michael; Gross, Katherine L.; Haddad, Nick M.; Pastore, Melissa A.; et al (August 2022, BioScience)

   abstract Long-term observations and experiments in diverse drylands reveal how ecosystems and services are responding to climate change. To develop generalities about climate change impacts at dryland sites, we compared broadscale patterns in climate and synthesized primary production responses among the eight terrestrial, nonforested sites of the United States Long-Term Ecological Research (US LTER) Network located in temperate (Southwest and Midwest) and polar (Arctic and Antarctic) regions. All sites experienced warming in recent decades, whereas drought varied regionally with multidecadal phases. Multiple years of wet or dry conditions had larger effects than single years on primary production. Droughts, floods, and wildfires altered resource availability and restructured plant communities, with greater impacts on primary production than warming alone. During severe regional droughts, air pollution from wildfire and dust events peaked. Studies at US LTER drylands over more than 40 years demonstrate reciprocal links and feedbacks among dryland ecosystems, climate-driven disturbance events, and climate change. 

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4. Increased mortality of tropical tree seedlings during the extreme 2015-16 El Niño - dataset and code

   https://doi.org/10.6084/m9.figshare.14204258.v1  

   Browne, Luke; Markesteijn, Lars; Engelbrecht, Bettina M.; Andrew Jones, F. Jones; Lewis, Owen T.; Manzané-Pinzón, Eric; Wright, S. Joseph; S. Comita, Liza Comita (January 2021, figshare)

   'Panama-El-Nino-publish.zip' contains all the code and data necessary to reproduce the analyses in the manuscript. Please unzip the file and see README.md for instructions.</div>'rocker-geospatial-rstan.sif' is a Singularity container that comes with all necessary packages pre-installed. Please seed README.md in the 'Panama-El-Nino-publish.zip' file for instructions.</div></div>Abstract</b></div>As extreme climate events are predicted to become more frequent due to global climate change, understanding their impacts on natural systems is crucial. Tropical forests are vulnerable to droughts associated with extreme El Niño events. However, little is known about how tropical seedling communities respond to El Niño-related droughts, even though patterns of seedling survival shape future forest structure and diversity. Using long-term data from eight tropical moist forests spanning a rainfall gradient in central Panama, we show that community-wide seedling mortality increased by 11% during the extreme 2015-16 El Niño, with mortality increasing most in drought sensitive species and in wetter forests. These results indicate that severe El Niño-related droughts influence understory dynamics in tropical forests, with effects varying both within and across sites. Our findings suggest that predicted increases in the frequency of extreme El Niño events will alter tropical plant communities through effects on early life stages.</div></div></div> 

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5. Droughts Amplify Differences Between the Energy Balance Components of Amazon Forests and Croplands

   https://doi.org/10.3390/rs12030525  

   Caioni, Charles; Silvério, Divino Vicente; Macedo, Marcia N.; Coe, Michael T.; Brando, Paulo M. (February 2020, Remote Sensing)

   Droughts can exert a strong influence on the regional energy balance of the Amazon and Cerrado, as can the replacement of native vegetation by croplands. What remains unclear is how these two forcing factors interact and whether land cover changes fundamentally alter the sensitivity of the energy balance components to drought events. To fill this gap, we used remote sensing data to evaluate the impacts of drought on evapotranspiration (ET), land surface temperature (LST), and albedo on cultivated areas, savannas, and forests. Our results (for seasonal drought) indicate that increases in monthly dryness across Mato Grosso state (southern Amazonia and northern Cerrado) drive greater increases in LST and albedo in croplands than in forests. Furthermore, during the 2007 and 2010 droughts, croplands became hotter (0.1–0.8 °C) than savannas (0.3–0.6 °C) and forests (0.2–0.3 °C). However, forest ET was consistently higher than ET in all other land uses. This finding likely indicates that forests can access deeper soil water during droughts. Overall, our findings suggest that forest remnants can play a fundamental role in the mitigation of the negative impacts of extreme drought events, contributing to a higher ET and lower LST. 

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