Non-Separable Spatio-temporal Models via Transformed Gaussian Markov Random Fields

TL;DR

This paper introduces a flexible class of non-separable spatio-temporal models called TGMRF, which simplifies interpretation and allows for custom marginal distributions, demonstrated through ecological data analysis.

Contribution

The paper presents a novel TGMRF framework that enhances non-separable spatio-temporal modeling with flexible dependence structures and interpretability, enabling new applications like spatio-temporal Gamma fields.

Findings

Identified environmental factors affecting snail abundance.

Characterized spatial and temporal trends in a tropical ecosystem.

Demonstrated model's applicability to ecological data.

Abstract

Models that capture the spatial and temporal dynamics are applicable in many science fields. Non-separable spatio-temporal models were introduced in the literature to capture these features. However, these models are generally complicated in construction and interpretation. We introduce a class of non-separable Transformed Gaussian Markov Random Fields (TGMRF) in which the dependence structure is flexible and facilitates simple interpretations concerning spatial, temporal and spatio-temporal parameters. Moreover, TGMRF models have the advantage of allowing specialists to define any desired marginal distribution in model construction without suffering from spatio-temporal confounding. Consequently, the use of spatio-temporal models under the TGMRF framework leads to a new class of general models, such as spatio-temporal Gamma random fields, that can be directly used to model Poisson intensity for space-time data. The proposed model was applied to identify important environmental characteristics that affect variation in the abundance of Nenia tridens, a dominant species of snail in a well-studied tropical ecosystem, and to characterize its spatial and temporal trends, which are particularly critical during the Anthropocene, an epoch of time characterized by human-induced environmental change associated with climate and land use.