An estimation of the contribution from TRMM-identified extreme storms to the total precipitation in South America

The TRMM (Tropical Rainfall Measuring Mission) satellite was designed to measure both the spatial and temporal variation of tropical rainfall around the globe and to understand the factors controlling the precipitation. For a complete perspective of the impact of intense precipitation systems on the hydrologic cycle in South America, it is necessary to assess the contribution from various forms of extreme storms to the climatological rainfall. This study is a comprehensive precipitation study, using all overpasses made by the TRMM Precipitation Radar (PR) over South America from 1998-2012. Previous studies showed that the TRMM PR algorithm underestimates heavy precipitation from intense convection in South America so we have used a more traditional Z-R method to assess the rainfall from intense radar echoes to mitigate this bias. An analysis of these precipitation data will be presented through seasonal, regional, and diurnal data.

The TRMM PR data are first used to investigate the relative contribution of precipitation from the TRMM-identified echo cores to the full storms in which the echo cores are embedded within on regional, seasonal, and diurnal scales by each separate storm type. The second part of the study assesses how much of the climatological rainfall in South America is accounted for by storms containing deep convective, wide convective, and broad stratiform echo components. Systems containing these echoes produce very different hydrologic responses. Extreme storm events with stratiform and convective elements lead to some of the highest rain contributions in specific regions throughout South America. Over 50% of the rain in subtropical South America from the austral fall through spring is contributed by extreme convective elements. During the austral warm season, regions that experience frequent mesoscale convective systems (MCSs) in the subtropics have convective rain contributions ranging from 50-60% of the total climatological rain. These numbers are very comparable to other precipitation contribution studies for warm season MCSs in the United States. From a hydrologic and climatological viewpoint, this empirical knowledge is critical, as the type of runoff and flooding that may occur depends on the specific character of the convective storm and has broad implications for the hydrological cycle in this region.