Characterizing spatiotemporal trends in extreme precipitation across the southern Texas coast

Rainfall extreme value analysis provides information that has been crucial in characterizing risk, designing successful infrastructure systems, and ultimately protecting people and property from the threat of rainfall-induced flooding. However, in the Houston region recent events (such as the unprecedented rainfall wrought by Hurricane Harvey) have highlighted the inability of existing analyses to accurately characterize current climate conditions. Specifically, there has been little research investigating how spatial patterns of extreme precipitation have shifted through time in the Texas Gulf Coast region, which has led to mischaracterization of existing IDF curves in the region. This study investigates spatiotemporal trends across the southern Texas coast using a novel statistical approach for peak over threshold modeling that employs an extended generalized pareto distribution. This method allows added flexibility by not requiring a threshold definition of what constitutes an extreme rainfall value. Since this value can vary over space, this method works well for our analysis of stations across a large spatial area. Precipitation data from over 600 rain gauges across the region are analyzed in 40 year time windows to evaluate shifts in distribution parameters and extreme rainfall levels through time. Spatial analysis of these trends focuses on highlighting regions with increasing, stationary, and decreasing extreme rainfall through time. Results demonstrate significant heterogeneity in spatiotemporal trends across the entire study region, but significant increases in extreme rainfall over the Houston urban area. Results from this study identify areas that have experienced significant shifts in extreme rainfall, and can help inform where design standards may be inaccurate or outdated.