Arid and semi-arid regions feature particularly vulnerable ecosystems. Quantitative approaches describing the interactions and feedback mechanisms between ecological, hydrological and hydrogeological processes are required not only to improve the current process understanding, but also to protect the remaining ecosystems amid ever-increasing anthropogenic pressure related to large-scale groundwater abstraction, mining and/or climate change. However, a range of challenges complicates this endeavour. For example, precipitation dynamics feature a high spatial and temporal variability, which leads to sporadic yet complex infiltration, evaporation and recharge dynamics and complex spatial flow patterns. Another example is evapotranspiration under arid conditions with many unresolved challenges such as nighttime evaporation, root water uptake or the plant response to drought stress. Moreover, aridity often comes with remoteness, which further complicates data acquisition.

In this special issue, we invite submissions that advance the current state of the art of ecohydrology, hydrology and hydrogeology of arid- and semi-arid areas. Contributions focusing on data acquisition for an improved process understanding are particularly interesting for this special issue. Examples of data acquisition include remote sensing approaches, innovative observation networks or ecological observations. Also, contributions for both small- and large-scale modelling approaches of hydrological and hydrogeological processes and dynamics and /or the interactions with ecohydrological processes are welcome. The integration of data into numerical models is also of high interest.