Atlas of precipitation extremes for South America and Africa based on depth-duration-frequency relationships in a stochastic weather generator dataset

Abstract

Information about extreme rainfall is lacking in regions of South America and Africa. This study attempts to fill this scientific gap by use of a gridded parameterization for the stochastic weather generator, CLIGEN, to map depth-duration-frequency (DDF) relationships. Analysis of 500-year point-scale precipitation time series generated at each grid point allowed maps of return period precipitation to be produced for a selection of sixteen durations ranging from 10-min to 1-year and for nine return periods from 2 to 500 years. The generalized extreme value (GEV) probability distribution was fitted for all durations, and given GEV quantiles, an interpolation method was applied to produce maps at 0.1° resolution that better resolve small-scale spatial climate gradients. In addition to uncertainties related to GEV fitting, this study quantifies prediction intervals based on ground validation. This validation was important for identifying biases in CLIGEN, although uncertainties were not always satisfactorily defined due to sampling design and other factors. For daily/multi-day durations, 100 stations with daily observations and ≥50-year records were selected for validation against the 0.1° CLIGEN map series, resulting in a median and average absolute error of 13% and 16%, respectively. For sub-daily durations, prediction errors were larger overall. An analogy using available U.S. data established the degree of bias in CLIGEN for sub-daily durations, and three records in Brazil with high temporal resolutions were used to confirm that applied bias adjustments resulted in error ranges similar to the daily/multi-day cases. This atlas is freely available for study of extreme precipitation.