In cities, climate change, Land Cover Mapping

Decades of scientific research have been suggesting that humans accrue many positive benefits from nature, whether that nature be in an isolated preserve, in urban green space within the confines of a city, or simply with a look at a painting of a forest.

As more than 70% of the world’s population will live in cities within the next 30 years, urban planning is becoming an increasingly critical topic. And, more and more scientists and planners recognize that urban green space need to be central to that planning. Such space includes parks, green roofs, cemeteries, and community gardens, and blue spaces, such as streams, lakes, and storm water retention ponds. Studies show that a shift towards urbanization will have major implications for human health, as more people will be exposed to the chronic conditions that are disproportionately high in cities, such as obesity, cardiovascular disease, and high blood pressure.  Therefore, mitigating factors, like urban green space, must be part of that urbanization.

What Does Urban Green Space Do?

Urban green space, like New York’s Central Park, not only provide recreational space, but also play an important role in environmental regulation.

Urban green space can minimize the prevalence of such chronic conditions because it promotes physical activity and general health of urban residents. Studies have found that green space in cities correlates with longevity, speedy recovery from surgeries, reduced stress, reduced asthma prevalence, reduced stress, improved cognitive ability, lower blood pressure and heart rate,  and self-reported improved happiness, all of which equate to better overall well-being.

Beyond these possibly direct health benefits, urban green (and blue) space provides critical ecosystem services within cities. For example, well-maintained urban nature promotes healthy soil, which supports more diverse plant life. Diverse plants help maintain soil moisture and replenish groundwater tables. Streams and ponds support permanent and migratory species of birds. And at least one study has shown that investments into green space, or ecological infrastructure, in urban areas is not just ecologically and socially advantageous, but may be economically advantageous as well. And, range of more subtle benefits can accrue from healthy urban ecosystems: enhanced social cohesion, improved community trust, and a sharpened sense of place-specific identity.

Some of the most useful ecosystem services provided by urban vegetation also include air filtration and heat buffering. As for the former, urban vegetation has been found to be effective in filtering tiny dust particles and pollutants from the air, reducing respiratory disease. The latter service (heat buffering) minimizes the “urban heat island effect,” which in turn can result in a cascade of potentially positive health and social effects: less urban heat can reduce the prevalence of heat-related illnesses, less mortality during heat waves, and possibly less crime or violence.

Where SIG Comes In

Given it’s GIS expertise, SIG has in recent years been involved in urban heat island mapping projects. In one case, SIG gave GIS support to Altostratus Inc. through a project to develop an Urban Heat Island (UHI) Index for the State of California. The UHI Index was developed so that the California Environmental Protection Agency (CalEPA), the State, and various city governments could have a heat index scale usable in a range of applications.

For example, some of the applications included: 1) an additional layer of information in the CalEnviroScreen 3.0 tool, which helps identify communities disproportionately impacted by multiple sources of pollution; 2) as way to target air-quality improvements from urban heat mitigation measures such by increasing park space or establishing green walls; and 3) as a way of identifying potential public health effects from heat islands and options for alleviating those impacts through better building design and urban planning.

To assist CalEPA in developing a UHI Index for California, Altostratus and SIG created a comprehensive, multi-scale atmospheric modeling and mapping study. It included fine-resolution meteorological and urban-vegetation modeling of urban heat islands. The entire state of California was modeled using mesoscale (the interface between weather and climate) and meso-urban models. Fine-scale meteorological characterizations and models were also used, but limited to select urban areas. The results were then translated into easily usable information for the CalEPA, city governments, and California regulatory agencies.

SIG mapped Sacremento’s urban forests in part to see if forests were related to social justice issues.

In a similar but unrelated project, SIG mapped the urban forests of Sacramento (video here).  While this study was not exclusively on urban heat, it did try to answer three pertinent questions. First, what is the distribution of tree carbon storage by parcel in the Sacramento region? Next, does this distribution shed any light on social justice inequalities? And finally, what impact does maintenance vehicle and equipment choice have on total project greenhouse gas emissions in the region? One conclusion was that reforestation efforts need to have and social justice components and focus on those areas where planting trees could make areas more livable.

California has been literally feeling the heat in more ways than one in recent years. The state has been hit with a series of forest fires, heatwaves, and droughts. Hopefully a better understanding of the fine-scale details of urban heat islands will help city planners begin to rehabilitate degraded urban lands and better design new ones. California and its residents have always been cutting-edge, but maybe now it’s time for them to be cool.

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