Title
Contrasting North–South changes in Amazon wet-day and dry-day frequency and related atmospheric features (1981–2017)
Date Issued
01 May 2019
Access level
metadata only access
Resource Type
journal article
Author(s)
Publisher(s)
Springer Verlag
Abstract
This study provides an updated analysis of the evolution of seasonal rainfall intensity in the Amazon basin, considering the 1981–2017 period and based on HOP (interpolated HYBAM observed precipitation) and CHIRPS (The Climate Hazards Group Infrared Precipitation with Stations) rainfall data sets. Dry and wet day frequencies as well as extreme percentiles are used in this analysis, producing the same results. Dry-day frequency (DDF) significantly increases in the Southern Amazon (p < 0.01), particularly during September–November (SON) in the Bolivian Amazon, central Peruvian Amazon and far southern Brazilian Amazon. Consistently, total rainfall in the southern Amazon during SON also shows a significant diminution (p < 0.05), estimated at 18%. The increase in SON DDF in the southern Amazon is related to a warming of the northern tropical Atlantic Ocean and a weakening of water vapour flux from the tropical Atlantic Ocean. The increase in DDF in the southern Amazon is related to enhanced wind subsidence (ascendance) over the 10°S–20°S (5°S–5°N) region and to a deficit (excess) of specific humidity at 1000–300 hPa south of 10°S (north of the 5°S), which suggest a reduction of deep convection over southern Amazonia. Subsidence over the southern Amazon shows a significant trend (p < 0.01), which can explain the significant increase in DDF. Wet-day frequency (WDF) significantly increases in the northern Amazon, particularly during the March–May (MAM) period (p < 0.01), producing an estimated rainfall increase during MAM of 17% (p < 0.01) between 1981 and 2017. Significant changes in both WDF and rainfall in northern Amazon have been detected in 1998 (p < 0.01). After 1998, the increase in MAM WDF and rainfall is explained by enhanced moisture flux from the tropical North Atlantic Ocean and an increase in deep convection over the northern and northwestern Amazon. These evolutions in DDF and WDF and in the tropical atmosphere occur simultaneously with an increase in sea surface temperature in the northern Atlantic Ocean, particularly after the mid-1990s. These results provide new insight into rainfall variability and climatic features related to increasing dry season length in southern Amazonia. Severe recent droughts may be associated with the increase in DDF in the South. In addition, the increase in MAM rainfall intensity in northern Amazon after 1998 may be associated with several historical floods that occurred after this date.
Start page
5413
End page
5430
Volume
52
Issue
October 9
Language
English
OCDE Knowledge area
Meteorología y ciencias atmosféricas
Oceanografía, Hidrología, Recursos hídricos
Scopus EID
2-s2.0-85053865162
Source
Climate Dynamics
ISSN of the container
09307575
Sponsor(s)
The authors acknowledge the PNICP-Peru for funding this research through the 397-PNICP-PIAP-2014 contract. JAM is funded by FAPESP/CNPq/CAPES INCT-Climate Change Phase 2 project (FAPESP Grant 2014/50848-9 and CNPq Grant 465501/2014-1). The authors are grateful to the SO-HYBAM observatory for providing rainfall data. We wish to thank the following agencies/organizations for providing access to data: the National Oceanic and Atmospheric Administration (NOAA)–Climate Prediction Center (CPC) for SST information and the ECMWF for ERA-Interim reanalysis data. The authors are grateful to Barbara Fraser and to the three anonymous reviewers for their contribution to improve this paper.
Sources of information:
Directorio de Producción Científica
Scopus