Estimation of soil moisture-precipitation interactions in South America using the Global Land Data Assimilation System

PABLO C. SPENNEMANN; A. CELESTE SAULO

Conferencia; WCRP Conference for Latin America and the Caribbean: Developing, linking, and applying climate knowledge; 2014

The main objective of this study is to identify regions where soil moisture anomalies influence subsequent precipitation and evapotranspiration anomalies, during the warm season in South America aimed at developing alternative tools for seasonal prediction, based on soil states. A statistical methodology, based on a ratio of lagged correlations, is applied to estimate the interactions between these variables using the Global Land Data Assimilation System (GLDAS) dataset. Possible impacts of remote forcing (e.g. ENSO) on these interactions are also examined. Our focus has been set over two sub-regions: Southeastern South America (SESA) and the continental part of the South Atlantic Convergence Zone (SACZ). Over tropical regions, parts of SACZ and in the southern part of South America positive and significant feedbacks between soil moisture and precipitation are found. Instead, significant negative feedbacks are found over SESA. The influence of ENSO over the soil moisture-precipitation coupling strength signal is evident over tropical regions. Likely physical mechanisms involved in the land surface-atmosphere interactions, the remote influence of ENSO and the role of precipitation persistence over extratropical regions will be discussed: it has been found that soil moisture-precipitation hot spots are sometimes largely driven by large precipitation autocorrelation at monthly scales. Despite that this methodology cannot be used to determine a precise causal-effect relationship between soil moisture and precipitation, this study documents a valuable first order approximation of land surface-atmosphere interactions over South America that complements pre-existing works.