Precipitation over Northern South America and Its Seasonal Variability as Simulated by the CMIP5 Models

Abstract

Northern South America is identified as one of the most vulnerable regions to be affected by climate change. Furthermore, recent extreme wet seasons over the region have induced socioeconomic impacts of wide proportions. Hence, the evaluation of rainfall simulations at seasonal and interannual time scales by the CMIP5 models is urgently required. Here, we evaluated the ability of seven CMIP5 models (selected based on literature review) to represent the seasonal mean precipitation and its interannual variability over northern South America. Our results suggest that it is easier for models to reproduce rainfall distribution during boreal summer and fall over both oceans and land. This is probably due to the fact that during these seasons, incoming radiation and ocean-atmosphere feedbacks over Atlantic and Pacific oceans locate the ITCZ on the Northern Hemisphere, as suggested by previous studies. Models exhibit the worse simulations during boreal winter and spring, when these processes have opposite effects locating the ITCZ. Our results suggest that the models with a better representation of the oceanic ITCZ and the local low-level jets over northern South America, such as the Choco low-level jet, are able to realistically simulate the main features of seasonal precipitation pattern over northern South America.

The South American monsoon variability over the last millennium in climate models

“…However, some models exhibit a double ITCZ over the eastern Pacific. This bias has been previously identified in CMIP3 and CMIP5 simulations, especially during austral summer and autumn seasons (Hirota and Takayabu, 2013;Sierra et al, 2015). Despite the limitations of model resolution, austral summer lower-tropospheric circulation simulated by the ensemble mean reproduces a cyclonic circulation over southeastern Bolivia (aka "Chaco low") as seen in observations and its associated northerly low-level jet, which is channelled by the Andes topography, transporting moisture to southern South America (Marengo et al, 2004).…”

“…Vuille et al, 2012). Recent studies indicate that the new generation of models included in the CMIP5 still tend to perform poorly in simulating precipitation in South America, especially over the Amazon Basin and the Atlantic ITCZ (Yin et al, 2013;Siongco et al, 2014;Sierra et al, 2015). However, CMIP5 models have shown further improvement in simulating precipitation over the region, in comparison to the CMIP3 generation (Jones and Carvalho, 2013;Yin et al, 2013;Hirota and Takayabu, 2013).…”

“…A stronger Atlantic ITCZ, for example, may contribute to enhanced surface divergence over tropical South America, inducing drier conditions in the region (e.g. , as observed in CMIP5 historical simulations (Yin et al, 2013;Sierra et al, 2015). However, a stronger local ITCZ does not necessarily translate into reduced SAMS rainfall since moisture convergence in this region is mainly influenced by the SACZ (Vera et al, 2009).…”

The non-stationary influence of the Atlantic and Pacific Niños on North Eastern South American rainfall

“…This region includes the Amazon region with one of the most intense convective activity areas in the world (Andreoli et al, 2012) and also the northeast of Brazil which is characterized by frequent and intense droughts due to its semiarid climate (Nobre and Shukla, 1996;Rao et al, 2006). The interaction between different atmospheric phenomena that appear in the whole region and local surface conditions (like topography, vegetation, and land use), generates a non-homogenous rainfall distribution that varies in a wide temporal and spatial range (Espinoza Villar et al, 2009;Sierra et al, 2015).…”

“…The annual cycle of precipitation over NESA is not completely explained by the ITCZ excursions, the existence of regional processes strongly influences the amounts of precipitation over the region, defining local rainfall patterns (Sierra et al, 2015). The position of the ITCZ also plays an important role in the connection of the rainfall variations over the Northeast of South America with rainfall anomalies in the Sahel region (Rao et al, 2006).…”