**Examining the Direct and Indirect E**ff**ects of Climatic Variables on Plague Dynamics**

**Ricci P.H. Yue \*,**† **and Harry F. Lee \*,**†

Department of Geography and Resource Management, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong

**\*** Correspondence: ricciyue@cuhk.edu.hk (R.P.H.Y.); harrylee@cuhk.edu.hk (H.F.L.)

† These authors contributed equally to the work.

Received: 15 March 2020; Accepted: 10 April 2020; Published: 15 April 2020

**Abstract:** Climate change can influence infectious disease dynamics both directly, by affecting the disease ecology, and indirectly, through altering economic systems. However, despite that climate-driven human plague dynamics have been extensively studied in recent years, little is known about the relative importance of the direct and indirect effects of climate change on plague outbreak. By using Structural Equation Modeling, we estimated the direct influence of climate change on human plague dynamics and the impact of climate-driven economic change on human plague outbreak. After studying human plague outbreak in Europe during AD1347–1760, we detected no direct climatic effect on plague dynamics; instead, all of the climatic impacts on plague dynamics were indirect, and were operationalized via economic changes. Through a series of sensitivity checks, we further proved that temperature-induced economic changes drove plague dynamics during cold and wet periods, while precipitation-induced economic changes drove plague dynamics during the cold periods. Our results sugges<sup>t</sup> that we should not dismiss the role of economic systems when examining how climate change altered plague dynamics in human history.

**Keywords:** climate change; plague; direct and indirect effects; Structural Equation Modelling
