Climate change poses a critical threat to the Pantanal, the largest wetland in the world. Models indicate an increase in the frequency of extreme precipitation events and extended periods of drought. These changes can amplify consequences for Pantanal's ecological functioning, which has already experienced intensive human modification of its hydrological system and environmental health. The present study analyzed the spatial and temporal dynamics of rainfall and resulting extremes in the Brazilian area of the Upper Paraguay River Basin (UPRB) along with a co-evaluation of the global Sea Surface Temperature data (SST). The predicted results indicate that wet extreme precipitation events will become more frequent in the highlands, while severe and prolonged droughts triggered by warming SSTs in the Northern Hemisphere (North Atlantic and North Pacific oceans) will affect the Pantanal. The linear relations between precipitation with SST of very specific oceanic regions and even from specific oceanic indexes obtained in the present study significantly improve the forecasting capacity, mainly from a resulting reduction to two months of the lead-time between SST warming to concomitant precipitation impacts, and by explaining 80% of Pantanal´s precipitation variation from major oceanic indexes (e.g., ENSO, PDO, NAO, ATL3). Current SST trends will result in inter-and intra-annual flooding dynamic alterations, drastically affecting the Pantanal ecosystem functioning, with consequences for wildlife diversity and distribution. Regarding the foreseeable global climate and land use change scenarios, the results from the present study provide solid evidence that can be used at different decision-making levels (from local to global) for identifying the most appropriate management practices and effectively achieving sustainability of the anthropic activity occurring in the Pantanal.

The Pantanal is the largest wetland of the world and one of the most important biodiversity hotspots in South America. An unprecedented ongoing megadrought is severely affecting its ecological functioning, flood pulse dynamics, and fire regime. Regarding this problematic, the present study generates reliable information about the following key issues: 1—Evolution and dynamics, 2—Origin and determinants, and 3—Forecast based on identified determinants and current trends. Results show that the evolution of the megadrought has been differentiable in both, space and time. As for its origin and determinants, Climate Change was ratified as one of the most important threats to the Pantanal, and to vast areas of South America, since a strong correlation was identified between megadrought’s dynamics and the occurrence of intense marine heatwaves at Northern Hemisphere oceanic waters, and more specifically, at the Northeast Pacific. Results also show that the megadrought is expected to continue at both the Pantanal and the surrounding Highlands, at least until December 2023. Thus, an intensification of fires risk, extending now to areas historically flooded or perhumid should be expected, concomitantly to a very negative impact on non-fire-resistant vegetation cover, as well as ecosystem functioning and biodiversity, perhaps even worse than those from 2020, widely covered by the international media.

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Species distribution modelling has become instrumental in assessing the influence of environmental conditions on the occurrence or abundance of taxa. The set of environmental layers used for this purpose is a crucial aspect, for which different climate‐based (bioclimatic) datasets have been recently developed. These bioclimatic variables result from combinations of precipitation and temperatures surfaces. Here, we explored both the performance and possibility of improving some of the currently available bioclimatic databases, through an evaluation of the precipitation and temperatures surfaces used to generate them. For this purpose, we used a combination of statistic and graphic approaches. We focused on Brazil, not only due to its natural megadiversity, but also due to its continental size and orographic heterogeneity: an excellent ground for refining methods replicable elsewhere. We found a better match between the climatic data measured on‐field and Tropical Rainfall Measuring Mission (TRMM 3B43 v7) in the case of precipitation, and the surfaces provided by the National Oceanic and Atmospheric Administration (NOAA) in the case of temperatures, sources uncommonly used for species niche modelling. We gauge‐calibrated the best performing surfaces using machine‐learning algorithms and generated corrected surfaces that allowed us to create BrazilClim: a database of bioclimatic variables, based on improved primary surfaces, which will result in more assertive predicted distributions and more actual pictures of the species' ecological requirements for megadiverse Brazil, an approach replicable elsewhere. All primary and bioclimatic surfaces generated for this study may be freely downloaded.

<p>Fire is a natural disturbance in the Neotropical savannas, and rather frequent in the relatively<br>dry and well-drained seasonal savannas of the Brazilian Cerrado. The neighboring Pantanal, on<br>the other hand, is a seasonally flooded savanna and the largest wetland in the world (≈138,000<br>km 2 ). Due to its wetter condition, fires in the Pantanal are much less frequent and spatially<br>restricted. But, given an ongoing extreme drought, the 2020’s fires in the Pantanal have been<br>unprecedented in extent and duration: About one third (≈45,000 km 2 ) of the area of this<br>important wetland has gone up in flames since last January. Regarding this historical drought,<br>climate change has been identified as one of the most important threats to the Pantanal.<br>Reductions in precipitation may cause significant disturbances in its ecological functioning,<br>affecting hydrological, floodplain inundation dynamics, as well as fire regime. Climate change<br>models from a recent study (Thielen et al. 2020, doi:10.1371/journal.pone.0227437) indicate<br>that, for the Pantanal, extended severe droughts are to be expected from the warming of Sea<br>Surface Temperatures (SST) at Northern Hemisphere oceans.<br>The present study analyses the spatial and temporal dynamics of precipitations during the<br>series 1981-2020 in the Upper Paraguay River Basin (UPRB), which comprises the Pantanal and<br>the neighboring Highlands, along with a co-evaluation of the SST trends at three oceanic<br>regions from Northern Hemisphere. Precipitation anomalies were analyzed by mean of the<br>Standardized Precipitation Drought Index (SPDI) based on the 1981-2010 climate normals.<br>Results show that for the UPRB, negative precipitation anomalies occur in pulses lasting<br>several years. A drought starting in 2019 has been the strongest and most extended on record,<br>persistently reaching the Extremely Dry condition (SPDI≤-2.0) during 2020. As early as Mar,<br>over 64% of the Pantanal is affected by such drought, and around 83% by Dec. For the UPRB,<br>four distinctive groups of subregions were identified according to their temporal dynamics of<br>mean SPDI values, mainly during Sep2019/Feb2020 and Mar2020/Dec2020. Here, precipitation<br>anomalies from southernmost subregions of the Pantanal were less intense and even not<br>affected by the drought.<br>As for SST, the Northeast Pacific region (PAC-NE) showed the most important dynamics. In this<br>region, SSTs have been anomalously warm since Jun 2019, with 64% of the time SSTA<br>surpassing the 90 th percentile: reaching the Heatwave condition. With a lead of one to two<br>months, PAC-NE showed the strongest (and negative) correlation with precipitation at UPRB<br>(r=-0.87) during Jan2019 to Dec2020. There is a significant trend for an increase in SST at the</p><p>Northeast Pacific, a trend that will certainly generate a rather continuous Heatwave in PAC-NE.<br>As a result, one expects an extension of the current extreme drought in the Pantanal area, at<br>least during 2021, and the intensification of fires with unprecedented duration and intensity,<br>extending now to areas historically flooded or perhumid. Concomitantly, we predict a most<br>definite impact on non-fire-resistant vegetation cover, as well as ecosystem functioning and<br>biodiversity.</p>