Environmental drivers

In GLOBIO(-Aquatic) environmental drivers are broad categories of factors that influence biodiversity directly. The term 'environmental drivers' is synonymous with ‘direct drivers’ as used in the Millennium Ecosystem Assessment (2005) and ‘pressures’ in the Driver – Pressure – State – Impact – Response framework.

GLOBIO-Aquatic is at present based on two (sets of) global environmental drivers of biodiversity change:

  1. Catchment land use and eutrophication
  2. Change in hydrological regime caused by damming, water withdrawal and climate change

Spatial information (maps) on these drivers forms the input of GLOBIO-Aquatic. For analyses on the global scale an important part of the input is generated using the Integrated Model for Assessment of the Global Environment (IMAGE). Based on scenarios and policy options, IMAGE simulates present and future status of the drivers. However, it is also possible to use other models to simulate the drivers.

Important in the calculation of drivers is the catchment approach, which implies that spatial relations based on flow direction are included. River catchments are identified based on a digital elevation map and the location of the water bodies according to the Global Lakes and Wetlands Database (GLWD).

The model currently describes the water bodies included in this map. Past and future loss of wetland area, through conversion into arable land, settlements and other human uses, is at present not covered by IMAGE. This aspect will be included in the future.

River basins of the world

1. Catchment land use and eutrophication

Catchment land use has an impact on biodiversity through nutrient and sediment losses to the water bodies. It is not only the type of land use which matters, but also the intensity of use.

Present state land use maps for GLOBIO are generated on the basis of land cover maps, such as GLC2000. The land cover maps are combined with various other data sources on land use intensity, such as data from FAO and national data. To project future land use often the IMAGE model is used, but also other models can be applied. For national and regional analysis often the model CLUE can be used to obtain more detailed input data.

Nutrient runoff from the land to the surface waters, both nitrogen and phosphorus, is modelled based on the agricultural area, the application of fertilizer and manure, precipitation and spatial characteristics such as slope, soil texture, amount of groundwater etc. Urban nutrient emissions are modelled as well, based on population, affluence, sanitation and the use of detergents .

The emissions to the surface water are accumulated following the water flow direction in the catchment areas of the rivers. Thus the nutrient loadings of the water bodies are determined (per grid cell). Also, the fraction human land use in the area upstream of that cell is calculated (per grid cell).

2. Change in hydrological regime

Physical alteration by river damming and water withdrawal causes changes in the hydrological regime of rivers. Also climate change, e.g. change in amount and timing of rainfall and evaporation, has an effect on hydrological patterns.

For GLOBIO-Aquatic river discharge is calculated, based on the water cycle (precipitation and evaporation patterns), the catchment map, and human influence such as the presence and management of dams and reservoirs, and water abstraction. This is done for the natural and the impacted situation. The environmental driver is calculated as the deviation between the natural and the impacted flow pattern.

Calculations of river discharge, both for the natural and the impacted situation, are carried out using the global hydrological and vegetation model  LPJ or the global hydrological model PCR-GLOBWB. Present and future state of the climate variables are simulated with IMAGE.