Marine heatwaves in the dynamics of the Pantanal&#180;s historical drought and unprecedented fires
Authors: Thielen Dirk , Ramoni-Perazzi Paolo , Marquez Marco , Quintero José I. , Rojas Wilmer , L. Puche Mary , Soto-Werschitz Irma A. , Thielen Kai , Nunes Ana , Libonati Renata 
Published: March 2021

&lt;p&gt;Fire is a natural disturbance in the Neotropical savannas, and rather frequent in the relatively&lt;br&gt;dry and well-drained seasonal savannas of the Brazilian Cerrado. The neighboring Pantanal, on&lt;br&gt;the other hand, is a seasonally flooded savanna and the largest wetland in the world (&amp;#8776;138,000&lt;br&gt;km 2 ). Due to its wetter condition, fires in the Pantanal are much less frequent and spatially&lt;br&gt;restricted. But, given an ongoing extreme drought, the 2020&amp;#8217;s fires in the Pantanal have been&lt;br&gt;unprecedented in extent and duration: About one third (&amp;#8776;45,000 km 2 ) of the area of this&lt;br&gt;important wetland has gone up in flames since last January. Regarding this historical drought,&lt;br&gt;climate change has been identified as one of the most important threats to the Pantanal.&lt;br&gt;Reductions in precipitation may cause significant disturbances in its ecological functioning,&lt;br&gt;affecting hydrological, floodplain inundation dynamics, as well as fire regime. Climate change&lt;br&gt;models from a recent study (Thielen et al. 2020, doi:10.1371/journal.pone.0227437) indicate&lt;br&gt;that, for the Pantanal, extended severe droughts are to be expected from the warming of Sea&lt;br&gt;Surface Temperatures (SST) at Northern Hemisphere oceans.&lt;br&gt;The present study analyses the spatial and temporal dynamics of precipitations during the&lt;br&gt;series 1981-2020 in the Upper Paraguay River Basin (UPRB), which comprises the Pantanal and&lt;br&gt;the neighboring Highlands, along with a co-evaluation of the SST trends at three oceanic&lt;br&gt;regions from Northern Hemisphere. Precipitation anomalies were analyzed by mean of the&lt;br&gt;Standardized Precipitation Drought Index (SPDI) based on the 1981-2010 climate normals.&lt;br&gt;Results show that for the UPRB, negative precipitation anomalies occur in pulses lasting&lt;br&gt;several years. A drought starting in 2019 has been the strongest and most extended on record,&lt;br&gt;persistently reaching the Extremely Dry condition (SPDI&amp;#8804;-2.0) during 2020. As early as Mar,&lt;br&gt;over 64% of the Pantanal is affected by such drought, and around 83% by Dec. For the UPRB,&lt;br&gt;four distinctive groups of subregions were identified according to their temporal dynamics of&lt;br&gt;mean SPDI values, mainly during Sep2019/Feb2020 and Mar2020/Dec2020. Here, precipitation&lt;br&gt;anomalies from southernmost subregions of the Pantanal were less intense and even not&lt;br&gt;affected by the drought.&lt;br&gt;As for SST, the Northeast Pacific region (PAC-NE) showed the most important dynamics. In this&lt;br&gt;region, SSTs have been anomalously warm since Jun 2019, with 64% of the time SSTA&lt;br&gt;surpassing the 90 th percentile: reaching the Heatwave condition. With a lead of one to two&lt;br&gt;months, PAC-NE showed the strongest (and negative) correlation with precipitation at UPRB&lt;br&gt;(r=-0.87) during Jan2019 to Dec2020. There is a significant trend for an increase in SST at the&lt;/p&gt;&lt;p&gt;Northeast Pacific, a trend that will certainly generate a rather continuous Heatwave in PAC-NE.&lt;br&gt;As a result, one expects an extension of the current extreme drought in the Pantanal area, at&lt;br&gt;least during 2021, and the intensification of fires with unprecedented duration and intensity,&lt;br&gt;extending now to areas historically flooded or perhumid. Concomitantly, we predict a most&lt;br&gt;definite impact on non-fire-resistant vegetation cover, as well as ecosystem functioning and&lt;br&gt;biodiversity.&lt;/p&gt;