Introduction

The history of migration is sculpted by water. Confronted by harsh and prolonged dry spells in East Africa’s Rift Valley over 5 million years ago, our ancestors decided to migrate and move across Africa in search of new sources of water. Scholars argue that this pivotal decision may have been key to their survival and the evolution of the human species (Cuthbert et al. 2017). Centuries later, human movement and migration have come to be recognized as one of the foundational drivers of economic development and growth. As explained in chapter 1, vast population movements from rural to urban areas and from agricultural to nonagricultural activities have been an important channel through which countries develop. By affecting movement, the availability of water has the potential to influence this process of transformation.

This chapter casts light on these development issues by investigating the relationship between water shocks and the internal migration mechanisms underlying the process of development at a global scale. The analysis uses a global and fine-grained data set spanning three decades for close to 150 countries to demonstrate the widespread nature of the effects while also uncovering significant heterogeneous impacts across different contexts. Results reveal that, overall, cumulative water deficits play a critical role in driving migration decisions. But these migration responses are conditional on income levels and notably on people’s ability to adapt to and to buffer their income against water shocks via investments in hydraulic infrastructure or leveraging nature’s ecosystem services or other buffering mechanisms (which might include savings from income).

These issues have far-reaching policy consequences. As economies develop, populations grow, and climate change takes hold, water shocks will pose an increasingly complex challenge to people. Scientists warn that twothirds of Earth’s land is already on track to lose water as the climate warms, with extreme-to-exceptional drought likely to affect more than double the area and population by the end of this century (Pokhrel et al. 2021). These estimates mean that nearly 700 million people, or 8 percent of the projected future population, could be affected by extreme drought, compared with 200 million over recent decades (Pokhrel et al. 2021). Understanding the uneven impacts across subsets of the population and the effectiveness of remedies that buffer incomes against water shocks will be critical to help inform the debate on future migration responses to continued climate change.

Because almost three times as many people migrate within countries than internationally, these questions are especially salient for internal migration (McAuliffe and Ruhs 2017). Past simulations project that an estimated 143 million people in Sub-Saharan Africa, South Asia, and Latin America will migrate within their own countries by 2050 in response to climatic variability (Rigaud et al. 2018). Some reports warn that massive waves of “water refugees” are likely to become commonplace as water runs