The accurate assessment of the potential impacts of climate change on societies and ecosystems requires regional and local‐scale climate change information. This assessment is critical for the development of local, national, and international policies to mitigate and adapt to the threat of climate change. Characterizing uncertainties in regional climate change projections (RCCPs) is therefore crucial for making informed decisions based on quantitative risk analysis.
However, information about fine‐scale climate change and associated uncertainties is lacking due to the absence of a coordinating framework to improve the characterization of such uncertainties. Here we propose the inception of such a framework.
The main characteristics of the atmospheric water vapor cycle over the South American continent and the adjacent oceans are investigated using the 22-yr period, from 1976 to 1997, of the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) 40-Year Reanalysis Project database. Precipitation rate and water vapor content fields obtained from this dataset are compared over the region with newly available observed datasets, which combine ground-based and satellite-derived observations. The temporal variation and spatial distribution of the atmospheric water vapor balance equation terms (precipitation rate, evaporation rate, and water vapor flux convergence) are examined with regard to their consistency and relative importance. The net effect of the atmospheric water vapor transport, represented in the last term of the balance equation, is decomposed into the horizontal and vertical convergence terms. The analysis of the latter highlights those regions where the topographic uplift makes a substantial contribution to the total precipitation rate. The former term is further decomposed into the stationary and transient water vapor flux contributions. The comparison of these terms with relevant characteristics of the large-scale tropospheric circulation provides a better understanding of the different precipitation regimes in South America. The mean annual balance satisfactorily closes over most of the oceanic regions. However, important imbalances found in the vicinity of high topographic features, such as in the central Andes, are attributed to large errors in the local computation of the atmospheric water vapor flux. The current results corroborate previous findings on the role of the stationary water vapor flux convergence in the spatial distribution and seasonal variation of the rainfall rate in tropical and subtropical latitudes and extend over the less-investigated continental midlatitudes. The magnitude of the transient water vapor flux convergence is, in general, lower than that of the stationary flux. Nonetheless, in some oceanic and continental regions, they are comparable and seem to be dynamically linked. This interaction, which can be explained by means of a simple transport-gradient model of the transient water vapor flux, could help to clarify the observed seasonal and interannual variability of the rainfall rate in the humid-to-dry transition zone in the southern part of the continent.
[1] We have investigated the relationship between extreme anomalies in the monthly precipitation of the Pampa Region (PR), Argentina, and large-scale circulation anomalies over the South American continent and the neighboring oceans. The composite maps of the extreme rainfall anomalies reveal that this atypical behavior extends beyond the PR and that comparable anomalies simultaneously take place in the center and south of Chile and in the western South Atlantic Ocean. We have analyzed the anomalies in the water vapor flux and in the circulation of the lower and upper levels of the troposphere that occurred in 85 months with extreme rainfall anomalies between 1955 and 1998. The study combines the use of a complete set of observed precipitation data and several atmospheric variables from the National Centers for Environmental Prediction Reanalysis. We have found well-defined anomalous circulation patterns that embrace the south of the continent and the vicinity of the Pacific and Atlantic Oceans, which are very similar but of opposite signs for both rainfall extremes. The interaction between these anomalies in the high-level flow and the subtropical jet stream generates the necessary conditions for vorticity advection and flow divergence, which is consistent with the expected vertical motions. The principal component analysis was applied to the pressure anomaly fields to distinguish those aspects of the large-scale patterns that are more directly related with the rainfall extremes. The amplitudes of some of the dominant PC are significantly correlated with the precipitation anomalies, and they highlight the mechanisms leading to rainfall extremes during El Niño-Southern Oscillation, and neutral periods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.