The role of topography in the global hydrological cycle

Topography influences how water is precipitated on, evaporated from, stored in, and routed through the landscape, often because of long-term evolutionary processes. How well do we know the links between topography and hydrology at large scales? Do we use this knowledge in, for example, large scale modelling efforts, or does topographic data contain information that is currently underused? To shed light on the role of topography in the global hydrological cycle, we explore three key themes.

First, topography leads to gradients and contrasts in climatic/weather forcing. Well-known examples are orographic precipitation, rain shadowing, or the presence of snow and ice at high elevations.

Second, topography is strongly related to different landforms, such as mountains and plains. These generic landforms provide a first broad classification, but there are further properties that vary along topographic gradients in a more nuanced way, such as sediment size or the depth of the critical zone.

Third, topographically induced differences in potential energy drive water movement. This can result in surface and subsurface flow across large (horizontal) distances, providing water to distant areas, and thus decoupling local hydrology to some extent from local climate.

The three themes (often in concert) describe partial controls on large scale hydrological processes and patterns. We derive several hypotheses based on these three themes, which would improve our understanding of large-scale hydrological processes, and help us in evaluating, constraining, and building hydrological models.