Spatial Observatory of Soil Water Content in Brittany
Water is an essential resource for humans and ecosystems: temporarily stored in the subsurface, it is consumed by vegetation and flows to rivers through hillslopes. In Brittany, 75% of water resources are exploited from surface water, supported by a set of small groundwater systems in the altered part of crystalline rocks. The lengthening of periods without precipitation induces agricultural and hydrological droughts (including in winter), threatening water supply systems, agricultural management schemes and efforts to restore the good ecological status of aquatic ecosystems (Figure 1). This climatic transition began in the 2000s and requires the adaptation of management tools, which must be based on dynamic observations of soil water content on a relevant scale, in addition to other meteorological and environmental architecture information. Until now, management tools have been based either on point or integrative observations (by "water mass"), or on models such as the SURFEX hydrometeorological model designed by Météo-France. However, its spatial resolution (64 km²) does not meet the needs of managers, particularly at plot scale (Figure 2).
Figure 1: Changes in temperatures and summer precipitation at 12 stations in Brittany since 1955. The temperature increases by 3.5°C per 100 years. The impact of climate change on summer precipitation is reflected in 2 precipitation regimes: from the 1960s to 2000, hot temperatures were associated with higher precipitation, but since the 2000s, hot years are water deficient. © Geosciences Rennes
The BOSCO project consists in:
- Deploying a validated satellite product (THEIA's very high spatial resolution moisture CES) for monitoring soil water content in the Brittany region with open access;
- proposing relevant indicators at local and regional scales and derived products to define water availability and thus meet the needs of agriculture, resource management and ecosystem monitoring;
- developing a platform for dissemination and integrated visualization (regional Copernicus approach GéoBretagne) to train and support stakeholders in the appropriation of products. Thus, these homogeneous and accessible data will allow to standardize the analyses, to ensure their transparency and to support the territories in their new competences (e.g. GEMAPI).
Figure 2: Parcel-scale distribution of water content in the Meu-Canut basin, west of Rennes, estimated by the CES THEIA product "Water content at very high spatial resolution". The white square corresponds to the SAFRAN/SURFEX analysis and modeling grid for estimating meteorological forcing and soil water content (Soil Water Index). Note the need for high spatial resolution to understand the specific high spatial variability in the behavior of hydrological systems. © Geosciences/CES THEIA
The project is built around research laboratories (code developers), companies (operational processing and derived products), ground observatories (data and product validation), and public end users (DREAL, Météo France, Eau du bassin rennais, Chamber of Agriculture) in charge of risk management and implementation of public policies related to agriculture, resource management, and ecosystem protection. The project also relies on "facilitators", i.e. expertise centers that actively participate in the use and development of satellite data (GIS BRETEL), the dissemination of data through accessible tools (GéoBretagne) and the development of environmental data in the territories (GIP OEB, Observatory of the Environment in Brittany). The Brittany region offers a very favorable context, as it is very involved in the development of spatial monitoring tools, and invested in the development of a regional policy for climate change mitigation. The project is part of the CNES-Region Bretagne framework agreement and will contribute to the development of the IRISPACE institute (Regional Institute for Space Innovation) which will start in 2021.
TERRITORY FOR EXPERIMENTATION
Brittany region, France
- Sentinel1 radar
- Sentinel 2 multispectral
- DREAL : General Land Register Data and River flow
- METEO-France : Precipitation, evapotranspiration
- Ground observations: water content, geophysical data, recharge estimates
To estimate the water content at very high spatial and temporal resolution at the scale of Brittany, the BOSCO algorithm relies mainly on the constellation of satellites from the European Copernicus program. It combines Sentinel-1 (radar, moisture sensitive) and Sentinel-2 (optical/NDVI, vegetation status) data within a neural network to estimate soil water content over a thickness of ~5 cm with an accuracy of ~5% by volume. The estimator is based on realizations of a physical model, calibrated on 10 years of data collected in different climatic and soil contexts. The approach is not sensitive to cloud cover. The singularity of this product remains its spatial resolution, one parcel, relevant for agricultural and water resources management issues, and its temporal scale (2 days), relevant for understanding water flows. The estimation of water content in the root zone and of recharge requires meteorological forcing (SAFRAN/SURFEX analysis) which will be provided by Météo France, information on soil type (GéoBretagne) and river flow data for calibration (DREAL).
The validation of satellite products and derivatives relies on a set of "ground" environmental observatories, gathered in an observation platform supported by INRAE and CNRS laboratories (UMS OSUR and UMS IUEM), and associated with the research infrastructures OZCAR and RZA. The tools and data for measuring soil water content (by drone, continuous monitoring), local information (pedology, ...) and expertise on the functioning of the observed systems will be made available for satellite date validation on a fine scale. Météo-France will also provide the outputs of the SURFEX model and in particular the SWI soil moisture index for the validation of raw and derived products on a large scale.
RESULTS - FINAL PRODUCTS
- Water content at very high spatial (plot) and temporal (2-3 days) resolution
- Estimation of water content on root thickness (plot, 2-3 days)
- Recharge estimate (plot 2-3 days)
The main data dissemination tool will be integrated in the "Copernicus Regional" approach and will be associated with the Mviewer tool developed by the Brittany region, used and promoted by GéoBretagne. A visualization interface will be developed to valorize the continuous data flows (every 2-3 days), hosted and disseminated by the company KERMAP in the form of open data that will also feed the THEIA database (IR DATA TERRA). This interface will be able to visualize maps at different dates or from statistical operations (variability, persistence), to display the temporal evolution by object at different scales of interest for the users (plot, island, municipality, watershed). The technical specifications will be defined between the product suppliers, the platform developer and the business users, with the support of the facilitators.
The support of territories in the use of these products and decision support will be based on the GIP OEB, which develops specific dashboards for each territory, combining data of interest and relevant indices. The ongoing process of integrating local authorities into the governance of the OEB will encourage the definition of tools targeted to their needs, associated communication, and, if necessary, the organization of training. Multi-criteria dashboards based on decision-making tools combining mapping and statistical processing results could be deployed (example here).