WaterGAP3
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
WorldQual
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)
