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1. Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century

   https://doi.org/10.1073/pnas.2002411117  

   Morales, Mariano S. ; Cook, Edward R. ; Barichivich, Jonathan ; Christie, Duncan A. ; Villalba, Ricardo ; LeQuesne, Carlos ; Srur, Ana M. ; Ferrero, M. Eugenia ; González-Reyes, Álvaro ; Couvreux, Fleur ; et al ( July 2020 , Proceedings of the National Academy of Sciences)

   South American (SA) societies are highly vulnerable to droughts and pluvials, but lack of long-term climate observations severely limits our understanding of the global processes driving climatic variability in the region. The number and quality of SA climate-sensitive tree ring chronologies have significantly increased in recent decades, now providing a robust network of 286 records for characterizing hydroclimate variability since 1400 CE. We combine this network with a self-calibrated Palmer Drought Severity Index (scPDSI) dataset to derive the South American Drought Atlas (SADA) over the continent south of 12°S. The gridded annual reconstruction of austral summer scPDSI is the most spatially complete estimate of SA hydroclimate to date, and well matches past historical dry/wet events. Relating the SADA to the Australia–New Zealand Drought Atlas, sea surface temperatures and atmospheric pressure fields, we determine that the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) are strongly associated with spatially extended droughts and pluvials over the SADA domain during the past several centuries. SADA also exhibits more extended severe droughts and extreme pluvials since the mid-20th century. Extensive droughts are consistent with the observed 20th-century trend toward positive SAM anomalies concomitant with the weakening of midlatitude Westerlies, while low-level moisturemore »transport intensified by global warming has favored extreme rainfall across the subtropics. The SADA thus provides a long-term context for observed hydroclimatic changes and for 21st-century Intergovernmental Panel on Climate Change (IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasing greenhouse gas emissions.« less
2. Temperature Across Vegetation Canopy-Water-Soil Interfaces Is Modulated by Hydroperiod and Extreme Weather in Coastal Wetlands

   https://doi.org/10.3389/fmars.2022.852901  

   Zhao, Xiaochen ; Rivera-Monroy, Victor H. ; Li, Chunyan ; Vargas-Lopez, Ivan A. ; Rohli, Robert V. ; Xue, Z. George ; Castañeda-Moya, Edward ; Coronado-Molina, Carlos ( May 2022 , Frontiers in Marine Science)

   Environmental temperature is a widely used variable to describe weather and climate conditions. The use of temperature anomalies to identify variations in climate and weather systems makes temperature a key variable to evaluate not only climate variability but also shifts in ecosystem structural and functional properties. In contrast to terrestrial ecosystems, the assessment of regional temperature anomalies in coastal wetlands is more complex since the local temperature is modulated by hydrology and weather. Thus, it is unknown how the regional free-air temperature (T Free ) is coupled to local temperature anomalies, which can vary across interfaces among vegetation canopy, water, and soil that modify the wetland microclimate regime. Here, we investigated the temperature differences (offsets) at those three interfaces in mangrove-saltmarsh ecotones in coastal Louisiana and South Florida in the northern Gulf of Mexico (2017–2019). We found that the canopy offset (range: 0.2–1.6°C) between T Free and below-canopy temperature (T Canopy ) was caused by the canopy buffering effect. The similar offset values in both Louisiana and Florida underscore the role of vegetation in regulating near-ground energy fluxes. Overall, the inundation depth did not influence soil temperature (T Soil ). The interaction between frequency and duration of inundation, however, significantlymore »modulated T Soil given the presence of water on the wetland soil surface, thus attenuating any short- or long-term changes in the T Canopy and T Free . Extreme weather events—including cold fronts and tropical cyclones—induced high defoliation and weakened canopy buffering, resulting in long-term changes in canopy or soil offsets. These results highlight the need to measure simultaneously the interaction between ecological and climatic processes to reduce uncertainty when modeling macro- and microclimate in coastal areas under a changing climate, especially given the current local temperature anomalies data scarcity. This work advances the coupling of Earth system models to climate models to forecast regional and global climate change and variability along coastal areas.« less
3. 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 )

   Abstract

   &#39;Panama-El-Nino-publish.zip&#39; 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><br /></div><div>&#39;rocker-geospatial-rstan.sif&#39; is a Singularity container that comes with all necessary packages pre-installed. Please seed README.md in the &#39;Panama-El-Nino-publish.zip&#39; file for instructions.<br /></div><div><br /></div><div><div><b>Abstract</b></div><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><br /></div>
4. Disentangling the impacts of human and environmental change on catchment response during Hurricane Harvey

   https://doi.org/10.1088/1748-9326/ab5234  

   Sebastian, Antonia ; Gori, Avantika ; Blessing, Russell B. ; van der Wiel, Karin ; Bass, Benjamin ( November 2019 , Environmental Research Letters)

   Flooding is a function of hydrologic, climatologic, and land use characteristics. However, the relative contribution of these factors to flood risk over the long-term is uncertain. In response to this knowledge gap, this study quantifies how urbanization and climatological trends influenced flooding in the greater Houston region during Hurricane Harvey. The region—characterized by extreme precipitation events, low topographic relief, and clay-dominated soils—is naturally flood prone, but it is also one of the fastest growing urban areas in the United States. This rapid growth has contributed to increased runoff volumes and rates in areas where anthropogenic climate changes has also been shown to be contributing to extreme precipitation. To disentangle the relative contributions of urban development and climatic changes on flooding during Hurricane Harvey, we simulate catchment response using a spatially-distributed hydrologic model under 1900 and 2017 conditions. This approach provides insight into how timing, volume, and peak discharge in response to Harvey-like events have evolved over more than a century. Results suggest that over the past century, urban development and climate change have had a large impact on peak discharge at stream gauges in the Houston region, where development alone has increased peak discharges by 54% (±28%) and climatemore »change has increased peak discharge by about 20% (±3%). When combined, urban development and climate change nearly doubled peak discharge (84% ±35%) in the Houston area during Harvey compared to a similar event in 1900, suggesting that land use change has magnified the effects of climate change on catchment response. The findings support a precautionary approach to flood risk management that explicitly considers how current land use decisions may impact future conditions under varying climate trends, particularly in low-lying coastal cities.

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5. Unpacking the climatic drivers of US agricultural yields

   https://doi.org/10.1088/1748-9326/ab1e75  

   Ortiz-Bobea, Ariel ; Wang, Haoying ; Carrillo, Carlos M. ; Ault, Toby R. ( May 2019 , Environmental Research Letters)

   Understanding the climatic drivers of present-day agricultural yields is critical for prioritizing adaptation strategies to climate change. However, unpacking the contribution of different environmental stressors remains elusive in large-scale observational settings in part because of the lack of an extensive long-term network of soil moisture measurements and the common seasonal concurrence of droughts and heat waves. In this study, we link state-of-the-art land surface model data and fine-scale weather information with a long panel of county-level yields for six major US crops (1981–2017) to unpack their historical and future climatic drivers. To this end, we develop a statistical approach that flexibly characterizes the distinct intra-seasonal yield sensitivities to high-frequency fluctuations of soil moisture and temperature. In contrast with previous statistical evidence, we directly elicit an important role of water stress in explaining historical yields. However, our models project the direct effect of temperature—which we interpret as heat stress—remains the primary climatic driver of future yields under climate change.