The Global Hydrological Status and Outlook System – monitoring and predicting global freshwater hydrological conditions 

Global hydrological conditions of floods and droughts as well as potential conflicts in water use are some of the greatest challenges and threats facing the world’s population. Some 20 million people are at risk from flooding with the associated damage costing nearly US$80 billion; this could rise to 50 million people affected in just 15 years time, according to the World Resources Institute. The World Economic Forum estimates that the effects of drought across the world cost up to US$8 billion a year from losses in agricultural and related businesses. These challenges will only intensify with future climate change, population growth and increasing economic activities. There will be 9.7 billion people living on our planet by 2050, according to the United Nations; this in itself presents a significant challenge in a world beset by hydrological variability on a global scale. Water features heavily in the new United Nations Sustainable Development Goals, not only in the explicit aim to ensure availability and sustainable management of water and sanitation for all but also because of the underpinning nature of water-related issues across many development areas.

Despite these looming issues, there is currently no operational global system capable of assessing the current status of surface and groundwater hydrological systems, or for predicting how they will change in the coming weeks and months. The need, therefore, for the WMO Global Hydrological Status and Outlook System (HydroSOS) cannot be clearer. The worldwide operational system will regularly report:

  • the current global hydrological status, including groundwater, river flow and soil moisture;
  • an appraisal of where the current status is significantly different from ‘normal,’ for example indicating potential drought and flood situations; and
  • an assessment of whether this is likely to get better or worse over coming weeks and months.

    Global Hydrological Status on soil moisture from June to August

From a scientific perspective, Numerical Weather Prediction and hydrological models are now sufficiently advanced to enable appropriate coupling for global-scale application at relevant spatial and temporal resolution, including ensemble approaches. Satellite data products are widely available to provide information on hydrometeorological variables and ground based observations are increasingly available globally. At its core the system would use:

  • Local-scale ground-based data: River flow, soil moisture, large lake levels and groundwater depths
  • Global/Regional-scale remotely sensed satellite data: Precipitation, soil moisture, aquifers and snow cover/depth
  • Global/Regional weather and climate forecast models: Precipitation and temperature
  • Global/Regional/Basin-scale hydrological models: River flow, soil moisture, groundwater

HydroSOS will directly build on existing and planned WMO initiatives in relation to hydrological monitoring, data sharing and sub-seasonal to seasonal meteorological forecasting, to deliver a unique operational system providing up-to-date hydrological information and products from National Meteorological and Hydrological Services to a range of end-users. This will be achieved by collaborating with different partners. While the system’s information and products will be global, they will also be provided at regional and national scales. The operational system will support the activities of National Meteorological and Hydrological Services and will provide easily accessible hydrological information and products that can be made accessible to government bodies, regional and international aid agencies, and the general public.

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Water is pre-eminent among environmental concerns critical to societal well-being.

Water-related hazards and threats are a source of deepening concern globally. Tens of millions of people worldwide are affected by these events, and damages are estimated to cost in the order of magnitude of billions of US dollars per year. Water hazards are consistently identified as among the highest global risks in terms of impact (World Economic Forum (WEF), 2020). And scientists expect water-associated risks to intensify in the coming years due to climate change, population growth and increasing economic activities.