Climatic conditions and child height: Sex-specific vulnerability and the protective effects of sanitation and food markets in Nepal

Approximately 25 percent of each year's worldwide cohort of infants grow up to be stunted, with dietary or disease conditions that limit linear growth in childhood contributing to poor educational attainment, low earnings, and high mortality rates later in life. In Nepal, stunting rates have been particularly high, with rates as high as 57 percent in 2001 before declining to 41 percent in 2011. Despite this improvement, Nepal remains one of the 10 countries in the world with the highest stunting prevalence, making it a high-priority location for research into increasingly effective ways of protecting children from harmful early-life circumstances. Socioeconomic factors associated with stunting in Nepal have been described by Headey and Hoddinott (2015), who show how changes in household and community-level characteristics help explain local variation and the overall improvement in this indicator from 2001 to 2011. Key changes involved both greater household sanitation and access to improved diets, which are pillars of the Nepal government's multisector nutrition plan. Despite this progress, however, poor sanitation and inadequate food intake remain widespread and are likely to be worsened by rising temperatures and more variable rainfall associated with climate change. Environmental conditions in early life are known to have impacts on later health outcomes, but causal mechanisms and potential remedies have been difficult to discern. This paper uses satellite data on vegetation near each child's home as an indicator of changing agroclimatic conditions, with randomness in the month of birth providing a natural experiment in the timing of exposure to more or less advantageous circumstances. Our use of variation in birth timing relative to changes in climatic conditions contributes to a rapidly growing body of literature using natural experiments to study the determinants of human health. Nepal is a landlocked country with a population of approximately 27 million people, of whom about 85 percent live in rural areas and are highly reliant on rain-fed agriculture. The country features three distinct ecological zones: Mountains, Hills, and Terai or lowlands, with varying population densities. The Mountain zone has a dry alpine climate and is situated at the highest altitude (>2500 m), with steep and rugged terrain and short growing seasons. The Hills have a mostly temperate climate (500–2500 m), and the Terai (<500 m) has a mostly subtropical and humid climate. The impacts of climate trends and fluctuations can be seen through changes in sowing dates, crop duration, crop yields, and management practices. Between 1978 and 2008, the summer months (May–August) became increasingly hot and wet, and winter months (November–February) became colder and drier. During that time, the higher levels of rainfall in summer increased rice yields but decreased yields for other crops, while lower levels of rainfall in winter decreased maize yields. For this paper, we use NDVI data to summarize the complex pattern of variation in both rainfall and temperature, providing a simple index of changing agroecological conditions in the area around each child's home. Our identification strategy takes a difference-in-differences approach, testing whether household sanitation and district-level food markets can protect children against the health consequences of unfavorable agroclimatic conditions at sensitive times in their early growth and development. We find that improved household sanitation and more commercialized food markets limit both kinds of vulnerability, providing significant protection from agroclimatic conditions for both pregnant mothers and infants. The underlying patterns are sex-specific, with systematic differences in how later heights relate to NDVI fluctuations that occurred during infancy and pregnancy. These differences are consistent with both gender bias in infant care and physiological differences in fetal development before the sex of the child is known.