Arboriculture & Urban Forestry 45(5): September 2019 The potential evapotranspiration (or reference evapo- transpiration, mm per month) for a typical month of 30 days with a 12-h photoperiod/day was modeled with an average temperature (T, o where I is a thermal index imposed by the local nor- mal climate temperature regime (Tn , o For temperatures above 26o Willmott et al. (1985) was used, in which ETM resented as: In order to convert the estimates from a standard monthly (ETM (ETD , mm per month) to a daily time scale , mm per day), the following correction factor (C) was used: where N is the photoperiod (h) for a given day. Estimates of water run-off for the five forest reserves studied were based on P90 (2004) with an assumed 10% run-off. In order to examine the potential usefulness of the forest reserves and their tree species for urban envi- ronments in the CNE region, the evapotranspiration estimates calculated for the reserves were compared with similar estimates for five cities throughout West- ern Europe that all represent rather different climates. These were Madrid (Spain), London (UK), Berlin (Germany), Copenhagen (Denmark), and Stockholm (Sweden). Climate data for the cities were taken from the websites of the Swedish Meteorological and Hydrological Institute (SMHI) (https://www.smhi.se/en) and the Danish Meteorological Institute (DMI) (http:// www.dmi.dk/en/vejr) (Table 2). Based on studies of C, the equation of is rep- C) and the expo- nent a is a function of I, both computed by: 225 C) using the scheme proposed by Thornthwaite (1948) and modified by Pereira and Pruitt (2004) as: urban morphology types by Gill (2006) and Deak Sjöman and Gill (2014), two different site situations were assessed: (1) high density urban areas (where imper- meable materials account for 79% of area); and (2) low density urban areas (where impermeable materials account for 43% of area). These two site situations were analyzed as regards: 1) the present climate and 2) a future climate scenario. For the CNE region, future climate scenarios predict an average increase of 2 to 6° C (3.6 to 10.8° F) in temperature, combined with more frequent heatwaves and periods of drought during summer (Gill et al. 2007; SOU 2007; IPCC 2014). In this study, a mean increase of 3° C (5.4° F) was assumed. Field Measurements In each forest reserve, five separate plots (30 m × 30 m [98 feet × 98 feet]) were established, resulting in a total of 25 plots with an allocated area of 4500 m2 (48,437.6 feet2 ). These plots were strategically placed within recognized forest stands, with particular atten- tion to areas with mature forests and homogeneous site conditions. All woody species at the forest reserve study sites were inventoried and classified into three different categories depending on the vertical distribution: upper canopy layer (UCL), lower canopy layer (LCL), and shrub level (SL) with plants < 1.5 m (5 feet). This classification helped delineate the toler- ance to warm and dry habitats depending on the posi- tion of species within the forest structure. Trees in the canopy layer modify the wind, humidity, and tem- perature microclimate for species in the understory layer (Oliver and Larson 1996). Thus, canopy species experience much more effective transpiration due to the exposure to wind and sun. In all study plots, the soil type, based on Uru- shadze and Ghambashidze (2013) and Urushadze et al. (2016), was identified by excavating 10 pits at ran- dom in each plot to a depth of 0.5 m (1.6 feet). Through this rough soil type determination, it was possible to draw qualitative conclusions on the water-holding capacity and make an assumption on available soil depth (Table 3). RESULTS Potential Water Stress in the Five Cities Under the Current Climate Calculations of the potential water stress (evapotrans- piration ETM, mm per month) in the five cities revealed ©2019 International Society of Arboriculture
September 2019
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
