Elastic Functional Changepoint Detection of Climate Impacts from Localized Sources

TL;DR

This paper introduces an elastic functional changepoint detection method that accounts for both amplitude and phase variability in climate data, improving detection accuracy over existing methods.

Contribution

The paper develops a novel elastic functional changepoint method capable of detecting both amplitude and phase changepoints in functional data, especially in climate studies.

Findings

Successfully detects amplitude and phase changepoints in simulated data.

Identifies temperature changes in stratospheric data post-Mt. Pinatubo eruption.

Outperforms existing methods in handling phase variability.

Abstract

Detecting changepoints in functional data has become an important problem as interest in monitoring of climate phenomenon has increased, where the data is functional in nature. The observed data often contains both amplitude ($y$-axis) and phase ($x$-axis) variability. If not accounted for properly, true changepoints may be undetected, and the estimated underlying mean change functions will be incorrect. In this paper, an elastic functional changepoint method is developed which properly accounts for these types of variability. The method can detect amplitude and phase changepoints which current methods in the literature do not, as they focus solely on the amplitude changepoint. This method can easily be implemented using the functions directly or can be computed via functional principal component analysis to ease the computational burden. We apply the method and its non-elastic competitors to both simulated data and observed data to show its efficiency in handling data with phase variation with both amplitude and phase changepoints. We use the method to evaluate potential changes in stratospheric temperature due to the eruption of Mt.\ Pinatubo in the Philippines in June 1991. Using an epidemic changepoint model, we find evidence of a increase in stratospheric temperature during a period that contains the immediate aftermath of Mt.\ Pinatubo, with most detected changepoints occurring in the tropics as expected.