Implications of Modeling Seasonal Differences in the Extremal Dependence of Rainfall Maxima

TL;DR

This paper investigates how seasonal changes in meteorological conditions affect the extremal dependence of rainfall maxima and demonstrates that modeling assumptions need to be adapted for different seasons to improve accuracy.

Contribution

It introduces an analysis of seasonal variation in extremal dependence of rainfall maxima and evaluates the performance of max-stable models across different seasons.

Findings

Brown-Resnick model performs well for summer rainfall maxima.

Model skill decreases significantly for winter maxima.

Seasonal dependence impacts model choice and accuracy.

Abstract

For modeling extreme rainfall, the widely used Brown-Resnick max-stable model extends the concept of the variogram to suit bloc maxima, allowing the explicit modeling of the extremal dependence shown by the spatial data. This extremal dependence stems from the geometrical characteristics of the observed rainfall, which is associated with different meteorological processes and is usually considered to be constant when designing the model for a study. However, depending on the region, this dependence can change throughout the year, as the prevailing meteorological conditions that drive the rainfall generation process change with the season. Therefore, this study analyzes the impact of the seasonal change in extremal dependence for the modeling of annual block maxima in the Berlin-Brandenburg region. For this study, two seasons were considered as proxies for different dominant meteorological conditions: summer for convective rainfall and winter for frontal/stratiform rainfall. Using maxima from both seasons, we compared the skill of a linear model with spatial covariates (that assumed spatial independence) with the skill of a Brown-Resnick max-stable model. This comparison showed a considerable difference between seasons, with the isotropic Brown-Resnick model showing considerable loss of skill for the winter maxima. We conclude that the assumptions commonly made when using the Brown-Resnick model are appropriate for modeling summer (i.e., convective) events, but further work should be done for modeling other types of precipitation regimes.