Climate change, geographic factors and plague dynamics in pre-industrial Europe

Abstract

Although numerous studies have shown linkages between environmental factors and plague transmission, their dominating approach is to address the linkage with modern data, with the absence of long-term observation of plague dynamics with the environment. Consequently, the resulting relationship largely constricts to area with plague activity nowadays and the observation ignores the impact of multi-decadal environmental change. This research employs the digitalized historical plague database in Europe created by Buntgen (2014) to explore the role of climate change and environmental factor on plague transmission in pre-industrial Europe, AD1347–1760. By focusing on the long-term pattern of plague transmission over a vast continent, this research is hoping to distinguish the hidden mechanism that determines the plague pattern we see nowadays in history and thus, providing insights for future epidemics control. In this study we explore plague transmission in two domains: spatial and temporal. In the spatial domain, we hypothesize that navigable rivers and major trade roles were dominating in spreading plague outbreak in pre-industrial Europe. Our baseline model proposes that plague recurrence is significantly related to distance of major trade route and navigable river and dimension of river. Verified statistically by historical demographic information, historical economic attributes and physical attributes, the baseline model assures the significant role of navigable rivers and major trade route in deciding plague transmission pattern in history. The hypothesis is also supplemented by historical evidence qualitatively. A schematic mechanism for spatial distribution of plague recurrence is proposed. In the temporal domain, we first examine how climatic factors (in terms of temperature and aridity threshold) drive plague transmission in pre-industrial Europe in the frequency domain. Our results suggest that there exists a strong multi-decadal (16–64 year) coherency between plague outbreak and the synergy of temperature and aridity threshold. Yet, the two climatic variables could not work separately in causing plague outbreak. Besides, such synergy is robust in facilitating plague transmission in different countries in Western Europe at the multi-decadal to centennial (16–128 year) temporal scale since AD1500, except Germany. The clue further leads to the consideration of multi-decadal climatic phenomenon in affecting plague dynamics. By dividing Europe into two marco regions (Atlantic-Central Europe and Mediterranean Europe) according to the different hydrological behaviors under North Atlantic Oscillation (NAO), we find that plague transmission in pre-industrial Europe is determined by the synergistic effect of NAO and lagged (~14–19 years) extreme temperature at the multi-decadal temporal scale. Based on our findings, the recent warming is equivalent to the period of extreme temperature, which could make the NAO-plague correlation in Europe negative. While NAO is currently in its positive phase, plague outbreak will be less likely.