Climate conditions can affect fertility through biological and behavioral mechanisms. Biological mechanisms include, for example, natural sterility, spontaneous intrauterine mortality, and duration of the fertile period. Behavioral mechanisms include, for example, perceptions that certain temperature and precipitation conditions can be unfavorable to births during particular seasons or due to weather shocks. The study developed by Leticia Junqueira Marteleto (University of Pennsylvania), Alexandre Gori Maia (UNICAMP), and Cristina Guimarães Rodrigues (FIPE/USP) analyzes the impacts of climate conditions on fertility over a period of a public health crisis in Brazil, the Zika epidemic. Findings suggest that increases in temperature and precipitation are associated with birth declines. The authors also show how fertility changes in response to climate conditions have increased during the Zika epidemic, particularly in urban areas.

The study (click here for full access) uses monthly data for Brazil's 5,664 municipalities across 72 months, from January 2013 to December 2018. The empirical strategy uses spatial fixed effect models to account for unobserved municipal heterogeneity and spatial dependence in the data. The study compares the effects of climate on fertility before and after the Zika epidemic, which took place in late 2015, when the Ministry of Health classified the increase in congenital malformations associated with Zika as a public health emergency. During the Zika epidemic, people may have redefined their fertility behavior based on their assessments of risk exposures to rainfall, which might consequently impact the association between climate and fertility. Transmission is greater during warm and wet conditions, increasing the risk of congenital malformation.

Findings show that both gradual and sharp increases in temperature are related to fertility declines. Similar results are found for gradual changes in precipitation. Extreme precipitation events significantly impact birth rates in rural areas only. These findings may be linked to behavioral channels via more profitable harvests during rainfall. The study also shows that birth rates declined remarkably during the Zika epidemic, especially after Zika's harmful consequences for fetal malformation were confirmed in late 2015. Moreover, the impacts of climate conditions on fertility were magnified during the Zika epidemic.

Fertility is particularly sensitive to extreme climate events during the Zika outbreak in urban areas. This is probably because arboviruses, in general, are more widespread in urban than in rural areas, and Zika, in particular, is largely an urban illness. Although urban areas are economically heterogeneous, urban poverty creates the ideal conditions for the proliferation of Zika and other arboviruses during warm and rainy periods. The urban poor in Brazil often live in areas with inadequate sanitation, infrastructure, garbage disposal, sewage treatment, and clean piped water access. Such circumstances lead to frequent home water storage, creating the ideal conditions for mosquito breeding and spreading arboviral illnesses. Such differences in physical exposure to the vector might have heightened perceived risks of arboviral infection, contributing to a disproportionate burden of arbovirus illnesses among urban populations. A second reason for a stronger effect of climate conditions on fertility during the epidemic in urban areas is that urban populations have more access to information on reproductive health and the means to act on their reproductive behaviors.