Background of WATSON

Drawning by Emel Zeray Öztürk

The Critical Zone is the thin dynamic skin of the Earth, extending from the top of the vegetation canopy through the soil, down to the bottom of the groundwater. It is the place where “rock meets life”, and where humans and most of the animals live, and it is therefore ‘‘critical’’ to our survival. The Critical Zone is the domain where water cycle dynamics connect the subsurface to vegetation, atmosphere and climate, controlling water quantity and quality.

Understanding water storage and transfer within the Critical Zone is vital to address key environmental and social problems linked to ecosystem services in natural and human-impacted environments: maintaining soil productivity in intensively managed systems, ensuring forest vitality, and improving landscape resilience to natural hazards. Such an understanding is pivotal to develop sustainable management and use strategies that can ensure a reliable and consistent supply of clean surface water and groundwater, including providing water for human consumption, industry and agriculture, which are all themes of growing concern in Europe.

The ongoing modifications in climate and land cover are altering the structure of the Critical Zone and affect the partitioning of water in the hydrological cycle. Knowledge of when and where groundwater resides in the subsurface, and the conditions under which plants access diverse water sources is necessary for comprehending vegetation and groundwater dependent ecosystems resilience to environmental changes, and remains a key challenge in Critical Zone studies.

Improving understanding and prediction of the effects of changing environmental conditions on water availability in agricultural and forested landscapes, climate, hydrological, and land surface models urgently require detailed information on water partitioning in the Critical Zone. This includes how much precipitation and/or irrigation water is stored in soils, recharges the groundwater, or is transpired by vegetation, and the temporal dynamics of these processes across different climates. However, the spatial and temporal scales of water moving through and mixing in the Critical Zone can be highly variable limiting the comprehension of the feedbacks between groundwater, soil water and vegetation.

Quantifying water fluxes and knowing time scales of transport is essential to understand transfer and retention of water and solutes in soil, which in turn control biogeochemical cycling and contamination persistence, offering crucial information to assess the vulnerability of water resources.

Objectives of WATSON

OpenAccess Database
To create European open-access databases of water isotope-based studies in the Critical Zone
To define protocols for standardized sampling procedures, and analysis techniques for stable water isotope data, providing training guidelines for future isotope applications in Critical Zone science.
To compare and assess state-of-the-art, isotope-based methods and models to estimate groundwater recharge, water sources for vegetation transpiration, and catchment-scale travel and transit time, as well as to analyse and summarize current technological approaches to collect and measure water isotope data.
Foster communication and collaboration between European researchers and water management agencies from different geographic regions responsible for water resource management, water use, land-use planning, forestry and agriculture
Facilitate interaction between scientists and other stakeholders, such as private laboratories involved in environmental analysis, to ensure transferability of the new analysis methods from the academic world to practise, and to translate current scientific knowledge on water transfer in the Critical Zone into tangible recommendations to effectively address water management needs.


WATSON will address three major scientific challenges through the activities of three interconnected Working Groups (WGs), with an extra WG dedicated to dissemination

Working Group

Challenge 1 - Groundwater recharge

What are the spatio-temporal patterns of groundwater recharge and mixing of groundwater and soil water across different climatic and physiographic regions? What factors affect the mixing and storage of different water sources in different climates, soils, or land uses? How do vegetation characteristics (e.g., species assemblage and spatial distribution) influence infiltration, percolation, and storage of water in the subsurface?

Challenge 3 - Residence and travel time

How do catchment-scale residence times and travel times vary across different climates and landscapes? How does plant water uptake affect catchment travel times? What modelling methods are best suited to derive consistent estimates of residence and travel times and how consistent are these estimates?

Challenge 2 - Vegetation water uptake and transpiration

How are precipitation and irrigation water partitioned into evaporation, vegetation interception, transpiration, soil water, and groundwater storage? What controls the spatio-temporal variations in vegetation water uptake from different soil depths and different water sources across a variety of climatic and physiographic regions? Which modelling approaches can be used to upscale plant water uptake patterns from the plant/stand scale to the catchment/landscape scale?

What are COST Actions?