Daily Rainfall Disaggregation to Estimate the Intensity-Duration-Frequency Relationship in Minas Gerais State, Brazil

HIGHLIGHTS

• An alternative method to sub-daily rainfall data for locals with scarce data.

• Intensity-duration-frequency curves were fitted by observed and disaggregation data.

• Assessment disaggregation coefficients for intensity-duration-frequency curves.

• Disaggregated sub-daily rainfall data adequately reproduced the IDF curves.

Abstract

Sub-daily resolution rain gauge data (pluviographic records) should be used to define extreme rainfall intensity-frequency-duration curves. However, there is a lack of these records for many countries, which leads to the application of rainfall disaggregation models that transforms maximum daily rainfall data into sub-daily depths. The agreement between the intensity-duration-frequency curves obtained with disaggregation models and using sub-daily rainfall data is necessary to support the disaggregation method's applicability. The daily rainfall disaggregation method using disaggregation coefficients is the most used in Brazil, despite the lack of performance evaluation. The linear regression and model identity test was used to compare the intensity of rainfall obtained with different methodologies to obtain intensity-duration-frequency curves in 116 rain gauges in Minas Gerais, Brazil. There is a significant difference between the maximum rainfall intensity (i_m) obtained from pluviographic records and those estimated by the daily rainfall disaggregation. Nevertheless, comparing the i_m estimated by the daily rainfall disaggregation methods and the i_m obtained by sub-daily rainfall data, good precision and accuracy are observed, especially using specific disaggregation coefficients. The disaggregation IDF relationships had an underestimation tendency of i_m, especially in larger return periods, which can be considered less harmful since the larger return periods are associated with higher safety projects. The practical result of this paper was the possibility of a simple and effective methodology to disaggregate the daily into a sub-daily resolution rainfall.

Keywords:
annual maximum daily rainfall; intense rainfall; soil and water management; sub-daily rainfall