05 Sep 2023
 | 05 Sep 2023
Status: this preprint is currently under review for the journal HESS.

Effects of soil moisture and surface heat fluxes on the South American Monsoon System over West-Central Brazil: an observational study

João Pedro Nobre, Manoel Gan, and Éder Paulo Vendrasco

Abstract. This study evaluated the relationship between different surface hydrometeorological variables and rainfall during the wet period of the South American Monsoon System (SAMS). A climatological study was performed for 30 rainy periods of the SAMS between the years 1991–2021 over the Central-West region of Brazil (WCB) (20–10° S and 60–50° W). The European Centre for Medium-Range Weather Forecasts Reanalysis 5th/ERA5 was used to understand, under different soil moist conditions (dry, intermediate, and wet), the hydrometeorological patterns and their impacts on SAMS during the three stages of the wet period: the development (September-October-November, SON), maturity (December-January-February, DJF), and weakening (March-April-May, MAM) South American monsoon quarters. The results show that along with an increase (decrease) in rainfall during the rainy season, there is also a significant increase (decrease) in both surface and subsurface volumetric soil moisture (θ) for the wet (dry) soil condition periods. However, the surface heat flux composites showed that the latent heat fluxes to the atmosphere (Hl) significantly exceeds the climatology during the SAMS development quarters (SON) for the wet soil group. In contrast, for the dry soil group, the significant increase of Hl, compared to the climatology, over the WCB occurred only during the SAMS maturity quarters (DJF), representing, in this last case, a significant injection of latent heat and consequently delayed evaporation (EV P) compared to rainy periods with wet soil, due to the low soil moisture content and the prevalence of dry convection over WCB. Regarding the sensible heat fluxes (Hs), it was observed drier (wetter) soils tend to exhibit values above (below) the climatological mean throughout all stages of SAMS evolution over the WCB. The 2-m air temperature (T 2m) and planetary boundary layer height (P BLH) anomaly composites showed that for the wet (dry) soil group and with significant rainfall above (below) the climatological mean over the WCB, all evolution quarters were marked by a significant decrease (increase) in T 2m and P BLH anomalies. Regarding the mechanisms of direct feedback between surface variables and rainfall associated with the SAMS, significant direct correlations were also observed between the mean rainfall of the SAMS rainy season and the mean values of active days duration (Dad), Hl, Hs and the surface Soil Moisture Condition Index (SMCI1).

João Pedro Nobre et al.

Status: open (until 31 Oct 2023)

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João Pedro Nobre et al.

João Pedro Nobre et al.


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Short summary
This study investigated the relationship between surface hydrometeorological variables and rainfall during the wet period of the South American Monsoon System (SAMS). We focused on the Central-West region of Brazil (WCB) and analyzed data from 1991–2021. We found that wetter soils were linked to increased rainfall, while dry conditions led to below-average rain. Latent heat fluxes, air temperature and planetary boundary layer height anomalies also varied with soil moisture levels.