Crop-damaging temperatures increase suicide rates in India

Abstract

More than three quarters of the world's suicides occur in developing countries, yet little is known about the drivers of suicidal behavior in poor populations. I study India, where one fifth of global suicides occur and suicide rates have doubled since 1980. Using nationally comprehensive panel data over 47 y, I demonstrate that fluctuations in climate, particularly temperature, significantly influence suicide rates. For temperatures above 20 °C, a 1 °C increase in a single day's temperature causes ∼70 suicides, on average. This effect occurs only during India's agricultural growing season, when heat also lowers crop yields. I find no evidence that acclimatization, rising incomes, or other unobserved drivers of adaptation are occurring. I estimate that warming over the last 30 y is responsible for 59,300 suicides in India, accounting for 6.8% of the total upward trend. These results deliver large-scale quantitative evidence linking climate and agricultural income to self-harm in a developing country.

Keywords: India; agriculture; climate; suicide; weather impacts.

Fig. 1.

Nonlinear relationships between temperature, precipitation, suicide rates, and crop yield: The response of annual suicides rates (deaths per 100,000 people) to (A) growing season and (B) nongrowing season temperatures. Response of annual suicide rates to cumulative (C) growing season and (D) nongrowing season rainfall. (E–H) Analogous relationships for log annual yield, valued in rupees per hectare. The slopes of the responses in A, B, E, and F can be interpreted as the change in the annual suicide rate or log yield caused by one day’s temperature rising by 1 °C. The slopes of the responses in C, D, G, and H can be interpreted as the change in the annual suicide rate or log yield caused by one additional millimeter of rainfall. All graphs are centered at zero.

Fig. 2.

Evidence for the agricultural income channel. Lagged effects of (A) growing season temperature and (B) high precipitation (years in which precipitation falls into the highest tercile of the long-run rainfall distribution) on annual suicide rates per 100,000 people suggest an economic mechanism for climate impacts. (C) Geographic heterogeneity in the suicide–temperature response, where states are colored by the state-specific temperature sensitivity as a fraction of the average treatment effect. Darker colors indicate more severe responses of suicide to growing season temperature; yellow indicates a negative effect. (D) Correlation between state-level suicide sensitivities and the additive inverse of corresponding state-level crop yield sensitivities. Temperature effects are shown as relative to the average treatment effect. Coefficients in all panels were estimated in a degree days model with a cutoff of 20 °C. Standard errors are clustered at the state level for suicide and district level for yield, and 95% CIs are shown around each point estimate.

Fig. 3.

Four tests of adaptation in the suicide–temperature relationship. Shown is heterogeneity in the suicide response to growing season degree days above 20 °C, (A) by terciles of long-run average growing season degree days, (B) by GDP per capita in 2010, (C) by periods within the sample, and (D) across two different estimation strategies (“long differences” estimates the effect of long-run climate trends, and “panel” estimates the effect of year-to-year variation). Shaded areas indicate the 95% CI around (A and B) the middle tercile response function, (C) the period 1983 to 1996, and (D) the panel method.

Fig. 4.

Attribution of suicides to warming trends in growing season temperatures since 1980: (A) trends in degree days above 20 °C during India’s main growing season for four example states and (B) the total number of deaths annually that can be attributed to warming trends, using the estimated marginal effects of degree days on suicide rates.