Economic studies of drought episodes typically use rainfall as a proxy for water scarcity, yet this is likely to lead to an endogeneity problem due to the correlation of variables that affect water scarcity (such as temperature and soil moisture) with relevant economic choices (such as which crops to grow or where to settle). This column presents an index that overcomes endogeneity by combining precipitation and potential water loss from the soil. The index can be used to improve our understanding of distributive politics and, in particular, of how political bias affects the assignment of drought-motivated aid relief.