05 Feb 2018

Portland Tree Removal

A couple of days ago, we have informed you about an interesting paper about the effects of giant sequoias on the microclimate in Portland, US. The study used ENVI-met as a computational fluid dynamics model to isolate the effects of sequoias on microclimates, and validated results by making field measurements.

Since we find the paper of the utmost importance, we would like you to give a deeper insight in the work.

Eckmann et al. (2017) measured microclimate effects with thirteen weather stations before and after the removal of four giant sequoias at the University of Portland, US, due to construction plans. Even though our ENVI-met database contains many different surfaces, soils and vegetation types, the authors gathered a great variety of site specific-material parameters and even created new vegetation with ALBERO. The university campus was rebuilt with every detail in a 2m-grid resolution and the simulation was executed on 6, July 2017. The in-situ measurements were performed on 6, July and after the tree removal on 14, July 2017, due to the occurrence of representative weather conditions for summer days with typical UHI effects on both days.

The results of the measurements and the simulation showed lower surface temperatures of -2K up to  -16K near to the sequoia canopies. The university’s former plan was to remove all eight giant sequoias, which surrounded one of the main campus buildings. The simulation without those eight trees displayed lower air temperatures of even -2K. Regarding wind speed and CO2-concentration, the results have shown that the tree presence reduced wind speeds in general, but different simulations with changing wind speed inputs enabled the reduction of CO2-concentrations over different areas of up to 6.2 ppm. And even lower wind speeds caused a reduction of CO2-concentrations.

In summary, the paper not only proves that giant sequoias can reduce the Urban Heat Island effect (summertime surface temperatures, near-ground air temperatures and CO2 concentrations), but also provides a well-documented and validly correct list of urban materials and vegetation, which might be very useful for our users in the future.

We would like to encourage you to have a look at this remarkable paper and keep in mind the authors’ insights, that trees verifiable improve the microclimate in their surroundings.