The assessment of global freshwater resources and flows forms the basis for analysis of water-related issues worldwide. This is needed to identify present and future problem areas (i.e., hot spots), estimate the impact of climate change, evaluate the effect of virtual water trade, and provide necessary data for international financing of water-related projects. In the last decades, large-scale modelling has become a key tool to assess the state of global freshwater resources. It offers the opportunity to assess global freshwater resources in areas where data availability is scarce. Another benefit of using hydrological models is the provision of temporally and spatially distributed information about the different components of the water cycle as model output e.g. to support groundwater monitoring or to assess actual evaporation which is difficult to measure

WaterGAP3 is a large-scale modelling framework that simulates the distribution and availability of water resources in terms of quantity and quality on a global scale. It is the latest version of WaterGAP (Water - Global Assessment and Prognosis) that has been developed at the Center for Environmental Systems Research (CESR) of the University of Kassel, Germany (Alcamo et al., 2003; Döll et al., 2003). WaterGAP3 is now further developed at Ruhr‑University Bochum (Germany). It consists of three main components:

  • a Hydrology Model to assess the natural water cycle,
  • a Water Use Model to assess human impact on the water cycle and
  • a Water Quality Model to assess the water quality in riverine systems.

The model works at a 5 by 5 arcmin global resolution (approximately 6 x 9 km in Central Europe). It simulates at a daily time step, though the model output is often used with a monthly resolution.

WaterGAP3 is used to investigate anthropogenic impacts such as climate change and socio-economic developments on freshwater resources in terms of quantity and quality on a global scale. It is highly variable because of its versatile modeling options and the different models within the framework which offers the opportunity to estimate long-term trends, taking into account modelling uncertainties.

Hydrology model

The hydrology model can be used to simulate the water cycle on a global scale, but also on a regional scale. It is a conceptual water balance model that includes the major water storage components, i.e., interception, soil water, snow, groundwater, and surface water. Due to its integration in the model framework, the hydrology model is particularly suitable for simulating future scenarios, as, for example, anthropogenic influences are also well represented in the model


WordQual is used to localize and predict large-scale water quality changes. The model can simulate both loads and concentrations of various pollutants in water bodies. Currently, the following substances are implemented in WorldQual: Biochemical Oxygen Demand (BOD), Fecal Coliform Bacteria (FC), Total Phosphorus (TP), and Total Dissolved Solids (TDS). Pollutant sources are defined as either point sources (e.g., wastewater treatment plants, industrial effluents) or diffuse sources (e.g., agricultural runoff) in the model, as shown in Figure 1. (UNEP, 2016) 

Information on runoff and water use is drawn from the other components of the WaterGAP3 model framework. This unique integration into the framework gives WorldQual the ability to incorporate water use changes into scenarios in addition to climatic changes, allowing a wide range of possible future developments to be examined.

Water Use Models

The water use models are several smaller models that simulate water withdrawals and consumption for different sectors. The water use of the following sectors is considered: thermal electricity production, manufacturing, domestic, livestock, and irrigation. After calculating water withdrawals and consumption, these are divided according to a regulated scheme into water withdrawals from surface water, water withdrawals from groundwater, and the so-called return flow (difference between water withdrawal and consumption), which quantifies the amount of water that is returned to surface water and groundwater. This information is used in the hydrology model and WorldQual to quantify anthropogenic influences on both water quantity and quality.


Application examples:

  • Flörke, M.; McDonald, R.; Schneider, R. (2018): Water competition between cities and agriculture driven by climate change and urban growth. In: Nature Sustainability 1, 51-58.
  • Fink, G.; Alcamo, J.; Flörke, M.; Reder, K. (2018): Phosphorus Loadings to the World's Largest Lakes: Sources and Trends. In: Global Biogeochemical Cycles 32-4, 617-634.
  • Eisner S.; Flörke, M.; Chamorro, A.; Daggupati, P.; Donnelly C.; Huang, J.; Hundecha, Y.; Koch, H.; Kalugin, A.; Krylenko, I.; Mishra, V.; Piniewski, M.; Samaniego, L.; Seidou, O.; Wallner, M.; Krysanova, V. (2017): An ensemble analysis of climate change impacts on streamflow seasonality across 11 large river basins. In: Climate Change 141, 401-471.
  • Malsy, M., Flörke, M., Borchardt, D., 2017: What drives the water quality changes in the Selenga Basin. Climate change or socio-economic development? Reg Environ Change. DOI: 10.1007/s10113-016-1005-4
  • Reder, K., Flörke, M., Alcamo, J., 2015: Modeling historical fecal coliform loadings to large European rivers and resulting in-stream concentrations. Environ. Modell. Softw. 63, 251–263.
  • Reder, K., Alcamo, J., Flörke, M., 2017: A sensitivity and uncertainty analysis of a continental-scale water quality model of pathogen pollution in African rivers. Ecological Modelling 351 (2017), 129–139.Schneider C.; Flörke, M.; De Stefano, L.; Petersen-Perlman, J. D. (2017): Hydrological threats to riparian wetlands of international importance – a global quantitative and qualitative analysis. In: Hydrol. Erath. Syst. Sci. 21, 2799-2815.
  • Voß, A., Alcamo, J., Bärlund, I., Voß, F., Kynast, E., Williams, R., Malve, O., 2012: Continental scale modeling of in-stream river water quality: a report on methodology, test runs, and scenario application. Hydrol. Processes 26 (16), 2370–2384.
  • Williams, R., Keller, V., Voß, A., Bärlund, I., Malve, O., Riihimäki, J., Tattari, S., Alcamo, J., 2012: Assessment of current water pollution loads in Europe: estimation of gridded loads for use in global water quality models. Hydrological Processes 26 (16), 2395–2410. DOI: 10.1002/hyp.9427


UNEP, 2016: A Snapshot of the World’s Water Quality: Towards a global assessment. United Nations Environment Programme. Nairobi, Kenya. 162pp.