Growing season length

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).
	ID	Title	Period	Statistical processing	Unit	Threshold	Comment
	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.
Calculation caveats	Spatial representation: S1 Other caveats: O3, O4 (thresholds also vary by vegetation species) Could be compared to: Could be used with:
Motivation	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 20^th century show a high degree of interannual variability (±15 days), primarily due to variations in air temperature.
Experience user
References	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.