Land-Surface Interactions with the Atmosphere Over the Iberian Semi-Arid Environment (LIAISE): Closing the Terrestrial Water Cycle

The terrestrial water cycle is impacted by human activity. With a growing world population, water resources become increasingly critical and require solutions such reservoirs and dams to increase storage capacities. In addition the increased food demand requires irrigation to optimise crop yields, further increasing the demand for water storage capabilities. These activities have some obvious impacts on the timing and volumes of discharge from rivers back to the oceans, but other impacts are largely unknown. For instance, how much of the irrigated water returns back into the river network and how does this vary with irrigation practices.

Semi-arid environments provide increased challenges for such water storage and irrigation practices and hence provide ideal locations for observational campaigns to help increase our understanding. The LIAISE (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment) observational campaign brings together ground based surface energy balance observations over a spring and summer period, with atmospheric boundary layer profiles during Special Observational Periods (SOPs) within the semi-arid environment of an approximately 10 km radius centered over the Lleida region of the Ebro basin. This area includes both irrigated and non-irrigated areas in an environment that is highly monitored, providing an opportunity to capture water use practices. The observational campaign will be complemented by long term precipitation, streamflow and irrigation use datasets to help understand the human impact on the terrestrial water cycle. Details of the ground-based observational network and the atmospheric profiles during the SOPs are given in other presentations, so here we describe the long term hydrological datasets.

In addition to describing the observational plans, we will also outline a modelling protocol that utilises the long term hydrological datasets in order to provide an understanding of the impacts of human activities on the terrestrial water cycle in this region of the Ebro basin, and how this might have changed over the past few decades. Detailed modelling studies within this protocol will enable the identification of the impact of differing irrigation practices that could help to inform future farming practices to optimally balance water demand from crop yields with that of drinking water.

As well as providing a basis for understanding the recent hydrological climatology of the Ebro basin, the detailed observations from LIAISE will enable an assessment of the various components of the terrestrial water cycle. The extensive ground-based observational sites will provide estimates of evaporation, whilst the streamflow measurements integrate the areal runoff processes. Hence LIAISE offers the opportunity for the first combined modelling comparison between land surface models and hydrological models which include the anthropogenic component. These two communities have traditionally modelled the terrestrial cycle from different ends of the problem, but LIAISE will provide the opportunity for both communities to challenge their models by evaluating all components in order to identify any strengths and weaknesses the two modelling approaches provide.