Exploring the interplay between human distance to rivers and drought events across Africa

Hydrological extremes, such as floods and droughts, are significantly affecting the human society and the environment. Whereas it is well-acknowledged that people after flood events tend to protect themselves against future events by either enhancing structural defenses such as river embankments, or moving away from flooded areas, we still do not know if people tend to move closer to rivers during or after drought events. To test this hypothesis, we analyze the mutual relation between human distance to rivers and drought events across Africa. In particular, we inspect how this relation changes in space and time from 1992 to 2013. To this aim, we use remotely sensed nighttime data, as a proxy of human presence and activity, and several distinct classes of distance to the river network to compute the human distance to rivers. Drought events are identified based on two alternative datasets: SPEI values and EM-DAT. Significant patters of decreasing human distance to rivers after drought events are found in several African countries. Our results show that droughts may trigger a higher human proximity to rivers, which then results in a higher exposure to floods, if a flood event is taking place, with remarkable damages and losses afterwards. Thus, the proposed methodology, by shedding light on the coevolution of society and drought, complements previous findings on the dynamics between people and floods.