GC098-0002
Drought and heatwave concurrent events in Southeast Brazil

Tuesday, 15 December 2020
Poster
João Lucas Geirinhas1, Ana Russo1, Renata Libonati2, Pedro M. Sousa1, Diego G. Miralles3 and Ricardo M. Trigo1, (1)Instituto Dom Luiz, University of Lisbon, Lisbon, Portugal, (2)Departamento de Meteorologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, (3)Ghent University, Hydro-Climate Extreme Lab (H–CEL), Gent, Belgium
Abstract:
Positive trends in frequency and severity of droughts and heatwaves have been reported for several regions like South America and particularly Southeast Brazil (SEB). Nevertheless, these regions still lack a comprehensive assessment of compound drought and heatwave (CDH) events. This study aims to (1) analyse the historical evolution of CDH events in SEB, to (2) characterize the land and atmosphere conditions as well as to (3) disentangle the physical mechanisms behind the observed record-breaking dry and hot events recorded during the 2013/14 and 2014/15 austral summer seasons.

Meteorological data, including maximum temperature (Tmax), were extracted from the ERA-5 reanalysis datasets. Soil moisture data were obtained from Global Land Evaporation Amsterdam Model (GLEAM v3.3a). Drought conditions were defined at a monthly scale and considering 3-month Standardized Precipitation Index (SPI) values <–1 . Heatwaves were defined as periods of consecutive days with daily Tmax values above a climatological calendar day Tmax percentile (80th, 90th, 95th percentile). A concurrent event was defined as a heatwave period that occurred during a month under drought conditions.

It was possible to conclude that the number of CDH events has increased over some particular regions of SEB. The recent summer seasons of 2013/14 and 2014/15 were examples of an association between droughts and heatwaves particularly over Minas Gerais, Rio de Janeiro and São Paulo states. This inter-relationship was controlled by two soil–atmosphere coupling regimes. The first regime (energy-limited) occurred during the first half of both summer seasons, in which consecutive hot periods coupled with a long-term precipitation deficit induced drought conditions. The absence of precipitation and the clear sky conditions maintained. Consequently, the severe dryness of the surface was enhanced, until a second high coupling regime (water-limited) was imposed, in which the hot events were amplified by the simultaneously drought conditions. At this stage, the surface started to disproportionally dissipate the incoming radiation as sensible heat, yielding the mega-heatwaves recorded over SEB during this period.

Acknowledgments: Ana Russo was supported by IMPECAF (PTDC/CTA-CLI/28902/2017) and ROADMAP (FCT, project 3599). Renata Libonati was supported by FAPERJ (grant E26/202.714/2019) and CNPQ (grant: 381461/2018-1).

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