POSITIVE is developing tools and techniques for integrating phenological, satellite and climate data for multipurpose use in the field of global change research.

Phenology

Europe is a particularly suitable region for one of the main goals of POSITIVE: Analysing trends in the vegetation cycle of the last several decades in Europe in order to assess past and possible future changes and using phenological observations to provide important 'ground truth' to earth observation programs and global change research.

Scientific objectives concerning the phenological data base are:
- to integrate in a consistent manner these phenological observations from different phenological networks .of several national weather services and from Post Soviet States for global change research.
- to analyse phenological trends of the last four decades in Europe, especially investigating the lengthening .of the growing season in Europe on a regional scale,
- to study the impact of altitudinal gradients on phenology for ground-satellite data comparisons, and
- to describe the geographical and temporal variability with a GIS database and to develop maps.

 

Climatological database and phenological models

Phenological phases are influenced by meteorological and environmental factors, such as temperature, light and radiation, wind speed, precipitation and water supply. Thus, on the one hand, phenological observations of plants can be used as biological indicators of changing environmental conditions. On the other hand, modelling of phenological phases allows an assessment of global change impacts in the future, such as changes of the length of the growing season, of the competition among species, of the risk of frost damage and of the endangering of humans by allergies (pollinosis). In addition, phenological modelling can attribute observed changes to certain influencing meteorological factors, which may have changed during the past decades.

The following scientific purposes have already been achieved:
- Pollen shedding models for tree and herbaceous taxa have been developed and tested. PPF - POSITIVE .Pollen Forecast, a Windows based software which allows predictions of pollen concentration curves at any .location, has newly been developed.
The following next steps will be accomplished in the second half of the project:
- to parameterise and validate phenological models for the springtime phenophases (bud burst, flowering) .and use them in a new distribution model for European species,
- develop and test new models for the autumn phenophases, and
- provide regional and Europe wide maps for model products.

 

Satellite data

Environmental monitoring is often made by indirect observations. For example, an advance in the seasonal vegetation cycle of about 7 days was inferred from CO2 data taken between the 1960s and early 1990s, with most of the effect occurring after 1980 (Keeling et al. 1996). Data sets of the Normalised Difference Vegetation Index (NDVI) for the 45-70° northern latitudes, observed from space platforms for the 1981-1991 period, also indicate that the photosynthetic activity increased and the beginning of the growing season advanced by 8±3 days (Myneni et al. 1997). POSITIVE uses newly available AVHRR NDVI land data sets, produced by the NASA Goddard Space Flight Centre (15 day composites, 8km grid, 1981-1998). In the second half of the project SPOT4 VEGETATION data will also be used.

Main scientific objectives hereby are:
- to analyse the temporal and spatial variability of the so called 'Green Wave' from 1981 to 1998,
- to quantify large-scale growing season duration and photosynthetic capacity for 1981-2000,
- to link ground observations and satellite data by a seasonal index model, and
- to study climate change impacts in different regions in Europe.