How much difference does shade make in the summer in downtown Pullman?

A lot.  Professor Steven Austin, a professor of landscape architecture, did a study with his students on a day when the air temperature was 82 degrees.  Surface areas without shade recorded 130.2 degrees, while areas in shade recorded 76.1 degrees.  That's 54 degrees difference on an 82 temperature day - the climate crisis is accelerating - what temperatures will downtown record without trees on a 100 degree day?   

Are the trees a threat to the sidewalks?  

No.    Trees lift sidewalks all over Pullman.  This common problem  can be fixed by taking out the sidewalk, pruning  roots and replacing the sidewalk.  The city is doing this on Pioneer Hill this summer, with a contract to Knox Concrete of Lewiston. They have done a good job.  There are 100-year-old + trees on College Hill. Sidewalks are smooth because the city replaced the sidewalks – not the trees –  about 20 years ago.  

Are the trees healthy?

Yes.  The downtown ash trees are healthy and probably have tapped into subsurface irrigation.  The roots of ash trees can go down up to 4 ft (USDA https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/fraxinus/pennsylvanica.htm).  Locations near the river like downtown Pullman have a high water table. The trees are not confined to what little water infiltrates through the 4-foot well. If the roots on the surface are pruned, the trees can still draw water through deeper roots.

Can sidewalks and trees co-exist?

Yes.  The engineering for replacing sidewalks around mature trees is established.  It has been done in Seattle.  This link describes an excellent effort that improved sidewalks and protected trees.     LEVY DOLLARS AT WORK | We built smoother sidewalks & protected mature trees on Aurora Ave N! - SDOT Blog  

Another excellent resource is available here:   https://gibneyce.com/18-read-about-sidewalk---tree-roots-conflict.html   

In short, trees and sidewalks are both necessary for successful downtowns --- and they can co-exist.   

Won’t the construction planned for downtown destroy the trees?

No.  Utilities that will be replaced are in the middle of the street, not under the sidewalks.  This includes sewer, water and storm drains.  There are established engineering protocols for working around mature trees (Cornell Urban Horticulture Institute). This involves creating a zone around the trees to prevent compaction and major excavation.