|Sector||Agriculture, Green infrastructure|
|Description||Leaf-on (leaf-off) is the date of onset (offset) of deciduous vegetation greenness. The dates refer to the aggregate phenology of ecosystem-scale understory and overstory conditions. Growing season length (GSL) describes the number of days the deciduous vegetation is active and no freezing conditions are encountered (i.e. frost free days). These variables are important for agricultural applications as well as determining ecosystem services, functionality, and health of ‘green’ urban infrastructure (e.g. hydrologic and carbon related processes associated with urban vegetation, green roofs, and green walls).|
|End User||Urban planners, agricultural sector, landscape architects, gardeners|
|Calculation method||Growing season length (GSL) is calculated as the number of days between the first 5-day period with average temperatures above 5°C (leaf-on date) to the first 5-day period with temperatures below 5°C (leaf-off date) (Buitenwerf et al, 2015; Donat et al, 2013; Mueller et al, 2015).|
|leafon||Leaf-on date||yearly||Day corresponding to the end of the first 5-day period with average temperatures above or equal to 5°C||day of year||
Interpreted as leaf emergence
|leafoff||Leaf-off date||yearly||Day corresponding to the end of the first 5-day period with temperatures below or equal to 5°C||day of year||
Interpreted as beginning of autumn senescence
|GSL||Growing season length||yearly||Leafoff – leafon||number of days||Interpreted as number of days between leaf-on and leaf-off dates|
|Provenance||Growing season length is based on temperature computed by the HARMONIE model.|
|Validation||The simulations made by HARMONIE-AROME in Urban SIS for the historical period have been validated against observations in Urban SIS deliverable 5.1, where an overview is given in Table 4.|
Growing season length (GLS) has been shown to increase by 4-6 days for every 1 K increase in annual average air temperature (White et al. 1999). GSL is an important variable determining carbon assimilation and evapotranspiration from vegetation and soils (Euskirchen et al. 2006) and it’s also an important constraint on agricultural productivity, particularly in northern Europe (Olesen et al. 2002).
There is a high degree of interannual variability in GSL. Modelled GSL based on air temperature, soil moisture, and solar radiation in North America during the 20th century show a high degree of interannual variability (±15 days), primarily due to variations in air temperature.
Buitenwerf R, L Rose, SI Higgins 2015: Three decades of multi-dimensional change in global leaf phenology. Nature Climate Change 5, 364-368.
Donat MG et al. 2013: Updated analyses of temperature and precipitation extreme indices since the beginning of the twentieth century: The HadEX2 dataset. Journal of Geophysical Research: Atmospheres 118, 2098–2118.
Euskirchen ES et al. 2006: Importance of recent shifts in soil thermal dynamics on growing season length, productivity, and carbon sequestration in terrestrial high‐latitude ecosystems. Global Change Biology 12.4 (2006): 731-750.
Mueller B et al. 2015: Lengthening of the growing season in wheat and maize producing regions. Weather and Climate Extremes 9, 47–56.
Olesen JE, M Bindi 2002: Consequences of climate change for European agricultural productivity, land use and policy. European journal of agronomy 16:4, 239-262.
White MA, SW Running, PE Thornton 1999: The impact of growing-season length variability on carbon assimilation and evapotranspiration over 88 years in the eastern US deciduous forest. International Journal of Biometeorology 42:3, 139-145.