Abstract
Abstract. The lack of rainfall data in Brazil, and, in particular, in Rio Grande do Sul State (RS), hinders the understanding of the spatial and temporal distribution of rainfall, especially in the case of the more complex extreme events. In this context, rainfall's estimation from remote sensors is seen as alternative to the scarcity of rainfall gauges. However, as they are indirect measures, such estimates needs validation. This paper aims to verify the applicability of the Tropical Rainfall Measuring Mission (TRMM) satellite information for extreme rainfall determination in RS. The analysis was accomplished at different temporal scales that ranged from 5 min to daily rainfall while spatial distribution of rainfall was investigated by means of regionalization. An initial test verified TRMM rainfall estimative against measured rainfall at gauges for 1998–2013 period considering different durations and return periods (RP). Results indicated that, for the RP of 2, 5, 10 and 15 years, TRMM overestimated on average 24.7% daily rainfall. As TRMM minimum time-steps is 3 h, in order to verify shorter duration rainfall, the TRMM data were adapted to fit Bell's (1969) generalized IDF formula (based on the existence of similarity between the mechanisms of extreme rainfall events as they are associated to convective cells). Bell`s equation error against measured precipitation was around 5–10%, which varied based on location, RP and duration while the coupled BELL+TRMM error was around 10–35%. However, errors were regionally distributed, allowing a correction to be implemented that reduced by half these values. These findings in turn permitted the use of TRMM+Bell estimates to improve the understanding of spatiotemporal distribution of extreme hydrological rainfall events.
Highlights
Characteristics of heavy rainfall events are important in the design of hydraulic structures, agriculture, weather modification, and in monitoring climate change (Angel and Huff, 1997)
This paper aims to verify the applicability of the Tropical Rainfall Measuring Mission satellite information for extreme rainfall determination in Rio Grande do Sul (RS) state extending its application for shorter duration rainfall by means of Bell’s (1969) equation
Regarding the daily rainfall with return periods (RP) ranging from 2, 10 and 25 years, the Tropical Rainfall Measuring Mission (TRMM) overestimated the values obtained from rainfall gauges data on average by 24.8 % with a standard deviation of 11.2 % (Fig. 1a)
Summary
Characteristics of heavy rainfall events are important in the design of hydraulic structures, agriculture, weather modification, and in monitoring climate change (Angel and Huff, 1997). Due to its highly complex spatiotemporal distribution its correct quantification is normally possible only through a dense rain gage network with quality data. This kind of network is financially unviable due to the high costs of monitoring and maintenance involved, especially in developing countries with large territorial extensions as Brazil (Fensteinseifer et al, 2013a). A quick research in the National Water Agency and National Weather Service of Brazil databases (in Portuguese known as ANA and INMET respectively) will show 881 daily rainfall gauges distributed in the 281 730.22 km of the state. When the focus is on shorter duration rainfall gauges, the research will show less than 30 stations with data, many of them with
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