Impact model: WaterGAP2-2ISIMIP2a

WaterGAP2 is a global water availability and water use model. Some introducing information can be found here: and at For participating in ISIMIP FastTrack we have used WaterGAP 2.2 (described in 10.5194/hess-18-3511-2014). WaterGAP2-2ISIMIP2a is a model version which is based on WaterGAP 2.2 (described in 10.5194/hess-18-3511-2014) but applied to the specifics of the simulation round ISIMIP2a. WaterGAP2-2c is a model version (WaterGAP 2.2c, described in 10.5194/hess-20-2877-2016) used for phase ISIMIP2b. Currently, we are re-running ISIMIP2a with WaterGAP2-2c to allow consistent assesments. For ISIMIP3, we will use WaterGAP2-2e (WaterGAP 2.2e) which is the successor of WaterGAP 2.2d (described in 10.5194/gmd-14-1037-2021).

Water (global)
Contact Person

Information for the model WaterGAP2-2ISIMIP2a is provided for the simulation rounds shown in the tabs below. Click on the appropriate tab to get the information for the simulation round you are interested in.

Basic information
Model Version: WaterGAP 2.2 (ISIMIP2a)
Model Homepage:
Model License: CC-BY-NC-4.0
Reference Paper: Main Reference: Müller Schmied, H., Adam, L., Eisner, S., Fink, G., Flörke, M., Kim, H., Oki, T., Portmann, F. T., Reinecke, R., Riedel, C., Song, Q., Zhang, J., and Döll, P et al. Variations of global and continental water balance components as impacted by climate forcing uncertainty and human water use. Hydrology and Earth System Sciences,20,2877-2898,2016
Reference Paper: Other References:
Person Responsible For Model Simulations In This Simulation Round: Hannes Müller Schmied
Output Data
Experiments: historical
Climate Drivers: GSWP3, PGMFD v2.1 (Princeton), WATCH (WFD), WATCH-WFDEI
Date: 2016-11-09
Spatial Aggregation: regular grid
Spatial Resolution: 0.5°x0.5°
Temporal Resolution Of Input Data: Climate Variables: daily
Temporal Resolution Of Input Data: Soil: constant
Additional Temporal Resolution Information: land cover from IGBP-classification based on MODIS land cover from the year 2004. Soil data from WISE Available Water Capacity (Batjes, 1996)
Input data sets used
Observed Atmospheric Climate Data Sets Used: GSWP3, Historical observed climate data, PGMFD v2.1 (Princeton), WATCH (WFD), WATCH-WFDEI
Other Data Sets Used: Reservoirs and dams, Land-sea mask, GRanD reservoirs & dams, River-routing network
Climate Variables: tas, rlds, rsds, pr
Additional Input Data Sets: GLWD for lakes and wetlands as well as GRanD for lakes and reservoirs
Was A Spin-Up Performed?: Yes
Spin-Up Design: Spin-up is in our case only to make sure that water storages behaves correctly with respect to the initialisation. We started the simulations in 1901 with 5 repeating initial years. We have no CO2 concentration included in the model.
Natural Vegetation
Natural Vegetation Partition: We only distinguishing IGBP classes based on MODIS data for the year 2004 and have a very simplified LAI development model for canopy evaporation.
Management & Adaptation Measures
Management: The model includes yearly varying irrigation area.
Extreme Events & Disturbances
Key Challenges: Correct simulation of low flows and high flows, from a climatic perspective modelling in dry regions; (climate) input data uncertainty, process representation in the model(s)
Additional Comments: No, details to the model and used input data are described in the reference papers.
Technological Progress
Technological Progress: Via water use models (details in Flörke, M., Kynast, E., Bärlund, I., Eisner, S., Wimmer, F., and Alcamo, J.: Domestic and industrial water uses of the past 60 years as a mirror of socio-economic development: A global simulation study, Global Environ. Change, 23, 144–156, doi: 10.1016/j.gloenvcha.2012.10.018, 2013.)
Soil Layers: 1 layer with 0.1-4 m depth (depending on land use)
Water Use
Water-Use Types: domestic, manufacturing, cooling of thermal power plant, livestock and irrigation sectors
Water-Use Sectors: irrigation, domestic, manufactoring, electricity, livestock
Runoff Routing: Linear reservoir, flow velocity based on Manning-Strickler
Routing Data: DDM30
Land Use
Land-Use Change Effects: Only static land use map is used (IGBP classification based on MODIS data from the year 2004). Irrigation area is varying from year to year.
Dams & Reservoirs
Dam And Reservoir Implementation: Water balance of reservoirs and big lakes are calculated in the grid cell that represents the outlet; reservoirs are in operation in its start year; reservoir algorithm after Hanasaki et al. (2006), described in Döll & Fiedler (2008), HESS
Was The Model Calibrated?: True
Which Years Were Used For Calibration?: Years where GRDC data are available for the specific basin (from 1920-2009) but max. 30 years with a preferred time span from 1971-2000 for WFD, PGFv2, GSWP3; and 1979-2008 for WFD_WFDEI
Which Dataset Was Used For Calibration?: We calibrated WaterGAP for each climate dataset using all water sectors. Additionally, we have homogenized temperature and radiation from WFD for WFDEI to overcome the offset between both forcings (method described in Müller Schmied et al 2016 (HESS, doi:10.5194/hess-2015-527) and calibrated with that; but used the not homogenized forcing WFD_WFDEI from ISI-MIP to run the simulation
How Many Catchments Were Callibrated?: All: 1319 basins, WFD (due to time limitation: 1312 basins), covering ~54% of global land surface (except Antarctica and Greenland)
How Is Vegetation Represented?: Temperature and precipitation based LAI-model, fixed rooting depth
Potential Evapotranspiration: Priestley Taylor with two alpha factors depending on the aridity of the grid cell
Snow Melt: Degree-day method