Why can a few centimetres of water flood many kilometres of a playa surface?

Playas are among the flattest landforms on Earth, which explains why a minimal amount of water can cover a vast area. Their surfaces typically feature slopes of less than 0.2 metres per kilometre.1

Because of this extreme level of flatness, when a few centimetres of water enter the basin, it spreads out to inundate many kilometres of the surface. This process of inundation is significant because it helps develop and maintain the near-perfect flatness that characterizes these desert landforms.1