https://www.sciencedaily.com/releases/2018/07/180718170302.htm

Cities often display many of the predicted effects of climate change, including higher temperatures, higher carbon dioxide concentration and higher drought rates. Some of those effects are due to impermeable building materials like concrete and glass, which help create "urban heat islands" and prevent water from soaking into soil.

Experiments in cities also have advantages over experiments performed in labs or in specially designed "growth chambers" that attempt to mimic higher temperature or drier soil conditions. Cities are larger than experimental chambers and organisms like trees have lived at higher temperatures their entire lives in cities, whereas other experimental methods can only increase temperature for short periods. Thus, urban areas can show how plants and animals respond to changes in climate over long stretches of time, which lab and growth chamber studies can't quite match.