Land hydrology, water availability for ecosystems and land surface models: what are we missing?

Land hydrology is a fundamental part of the global water cycle, and as such, of Earth’s climate system, including the biosphere. Yet, this basic component is still poorly represented in current models, partly because the structure of the land features scales much smaller than what those models can resolve, but also due to a lack of understanding of processes occurring below ground that are not readily at sight. Here we will examine from the perspective of what is important to the atmosphere from seasonal to centennial timescales, questions such as what groundwater and surface water do in shaping water availability and how vegetation and ecosystems adapt to it, ultimately modulating land-surface fluxes and climate. How relevant are these processes and what are we missing in current land-surface models?