Glendale ranked as the least sustainable city in the U.S. and three other Arizona cities were also named among the 10 worst for environmental efforts in a recent study.

The analysis, conducted by WalletHub, sought to determine which U.S. cities prioritize sustainability and invest most in protecting the environment. Analysts compared the 100 largest U.S. cities across 28 key indicators of environmental friendliness and sustainability, from greenhouse gas emissions per capita and water quality to job opportunities in sustainability.

The indicators were then grouped into four categories: environment quality, transportation habits and initiatives, energy sources and sustainability policies. Each city was assigned a score in every category and the scores were combined to come up with an overall ranking, from the cities leading in green initiatives to those falling behind.

Here's what environmental challenges are impacting Arizona cities the most, what local solutions could be implemented and simple ways people can contribute, along with a roundup of the most and least environmentally conscious cities in the U.S.

These are the 10 most sustainable cities in the U.S., according to WalletHub.

Here are the 10 least "green cities," ranked from least to most sustainable, according to WalletHub.

Glendale, Mesa, Gilbert and Chandler rated poorly across all study categories but were ranked especially low for environmental quality indicators like the intensity of the urban heat island effect, the share of green spaces, and air and water quality, among other factors.

Arizona counties are among those expected to be hardest hit by climate change within the next 20 years, with average annual temperatures and the number of days above 90 degrees expected to increase significantly, according to data from the Climate Impact Lab.

Fernando DePaolis, who has a doctorate in urban planning and teaches policy analytics at the Middlebury Institute of International Studies, said implementing climate adaptation policies is pivotal in Arizona cities where the impact of urban heat is expected to be exacerbated by droughts and serious changes in rain patterns, with fewer but more severe rains likely to become the norm.

The urban heat island effect is at the forefront of metro Phoenix's prolonged and worsening heat, as buildings, roads and other infrastructure absorb and re-emit the sun's heat. This contributes to higher low temperatures in the mornings, resulting in more record temperatures in the afternoons.

DePaolis said investing in urban reforestation and reducing the density of these heat accumulators would help reduce the number of days above 100 degrees in Arizona cities.

"(These) solutions are, in aggregate, more cost-effective. It is not just a way of being 'green'; it makes good business sense," DePaolis said in an email statement.

Phoenix is investing in creating more shaded areas in vulnerable areas, with leaders at the city's heat office putting up $50 million from local, federal and private funds into the initiative over the next five years.

The "Shade Phoenix Plan" presented in early June is an overhaul of the city's Tree and Shade Masterplan passed in 2010. The new plan, like the old one, focuses on educating the public about the importance of shade, increasing planted and built shade structures, and preservation and maintenance. The new plan follows a $10 million federal grant the city received in 2023 through the Biden Administration's Inflation Reduction Act, on top of $4 million from the American Rescue Plan Act the city allocated toward urban tree shade in 2022, plus $300,000 earmarked by Gov. Katie Hobbs in last year's state budget for the "Trees for Kids" program to create shade at schools.

At spot No. 72, Phoenix also underperformed in WalletHub's greenest cities ranking, but it was far ahead of the four Arizona cities named among the bottom 10. Phoenix ranked lowest in the transportation category but landed in the top half for sustainability policies.

Tucson, Mesa, Chandler, Peoria and other cities also received large sums of money from the U.S. Forest Service in 2023 as part of Biden's $1.5 billion urban forestry initiative, which is also part of his Justice40 plan to address the ways climate change will affect minorities and disadvantaged communities the most.

Besides adding more green spaces, here are some more cost-efficient green policies that McCusker and DePaolis said local authorities can implement to effectively foster environmental protection and alleviate the harmful effects of warming, especially in the most vulnerable communities:

Here are some simple ways people can implement environmental practices without much cost or effort, according to DePaolis and WalletHub analyst Chip Lupo: