WATCH has brought together hydrologic and climate scientists to produce an integrated
water cycle monitoring tool which can better describe the global water cycle. To achieve this task, climate data from 1901 to 2001 were compiled in a data set (Forcing Data). This database comprises eight fundamental climate variables measured in time-intervals of several hours: these data can be used in hydrological models to improve global water cycle understanding. Additionally, a new data set (Driving Data) was obtained to predict climate variables from 2001 to 2100. These data were obtained from three consolidated climate models, and were applied considering two different IPCC (Intergovernmental Panel on Climate Change) scenarios. As a result, six different data sets have been established in order to be used in hydrological models.
Forcing Data and Driving Data were used to analyse present and future behaviours with respect to:
Climate and hydrological relationships: different land-based and hydrological models were compared by making use of Forcing Data in order to assess river flows and evaporation in the world’s major river basins. A data analysing approach showed that current differences among models came from the evaporation process, which is expected to increase with climate change. Another contribution to uncertainty comes from groundwater reserves and exploitation, since it is difficult to obtain daily data over large regions.
This comparison has provided tools for assessing impacts on water cycle at global scale in the future, and has also allowed river flow estimations in areas where low data were available so far (e.g., river Congo basin).
Floods and droughts: compiled data were used to establish Europe flood and drought maps (Atlases), which show that Northern Europe has high mean annual flows whereas Southern Europe (drier) shows low mean annual flows.
Forcing Data were used for validating existing drought detection methods and identifying the best ones, and for assessing hydrological models for reproducing extreme conditions. Moreover, Forcing data were used successfully to predict droughts in small catchments.
Land use and evaporation: a new global evaporation data set between 1984 and 2007 was obtained thanks to geomatic monitoring data. Obtained data have shown a global land evaporation reduction in the past ten years, in opposition to expected trends due to climate change.
Evaporation depends strongly on land use, so maps of land cover change over the 20th century and future scenarios for the 21th century have also been established.
Water availability and demand: water scarcity and agricultural water use has been quantified with different climate models, and water availability has also been compared with water needs in order to obtain a balanced diet. The results have highlighted the importance of “green” water (water coming from rainfall and retained by soil) for global water-resource calculations and water scarcity studies.
Data sets of water usage for industrial applications have been obtained, revealing that water use for industrial production has increased 15-fold along 20th century.
Water and global change. The WATCH Project Outreach Report.