Interpreting heat mitigation index

Hello, I’m running the Urban Cooling Model for a research project. I read the User Guide various times (incl. the interpreting the results section as well as the model explanation), and I still do not understand exactly how to interpret the output raster of heat mitigation index. can it be interpreted as how much a certain pixel is relatively cooled through shade, albedo and evapotranspiration in its surrounding? I would really appreciate a closer explanation of how to interpret the values of the HMI raster. Like what does HMI 0.8 mean compared to another pixel that has HMI = 0.1. Thank you!

Hi @carolincarella,

Welcome to the forum and thanks for your question.

Yes, you are on the right track in terms of your interpretation of HMI. It is an index, so it’s values are only meaningful relative to one another. Remember that InVEST estimates ecosystem services, as in the beneficial contributions of nature. CC values represent the contribution of each pixel to cooling. And HMI values capture the combined magnitude of the impacts (to each pixel) of CC and nearby large green spaces. A pixel with an HMI of 0.8 is cooled by urban nature 8x more than a pixel with an HMI of 0.1, relative to UHImax.

For daytime-based analyses (the “factors” Cooling Capacity Calculation Method), yes, HMI represents how much a pixel is cooled through the shade, albedo, and ET of that pixel plus any effects from other pixels of nearby large green spaces (dependent on the Maximum Cooling Distance (dcool)). For nighttime based analyses (the “intensity” Cooling Capacity Calculation Method), HMI values represent cooling based on building intensity.



Hi @jesseG, thank you for your elaborate response. that is definitely very helpful!

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By rerunning the models I just wanted to check whether some of my outputs make sense. In some rural areas, I get pixels with HMI = 1 . I read in another post that an index of 1 is not always desirable necessarily as heat mitigation, so does that number as a result not really make sense in real world applications? Could it be that something in my data is off to lead to that result? Just checking if you have any input on this, that would be very helpful!

Hi @carolincarella ,

My interpretation is that an HMI value of 1 could be logical in rural areas since rural areas should not be subjected to urban heat island (UHI) effects. As in, the complete absence of a UHI in rural areas means that there’s nothing to mitigate. The model is intended for urban areas and is not necessarily applicable in rural locales.


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Hi @jesseG - thank you! That is very helpful! I was thinking that maybe the model requires some rural reference to calculate some values. But if it is not necessary, that helps me adjust my area of interest accordingly.

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I’m glad I’ve been helpful! Your AOI does not need to include rural areas. Per the User Guide, the only rural reference you must provide is a Reference Air Temperature (°C): “Air temperature in a rural reference area where the urban heat island effect is not observed.