Conclusions

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Population in the watershed between 1990 and 2000 increased at 36.25% from 250,876 to 341,814.  The significance of this related to land change gives some hard numbers to the increased inhabitants in the watershed.  Land cover change between 1996 and 2006 compared to 1990 and 2000 population change shows that there was approximately 0.21 acres per new inhabitant.

So we can see with the previous maps where the population increased and land cover changed, but not where these are happening relative to each other and relative to the MUGA.  Using the identity tool with ArcMap will select layers and will show what percent of changes are occurring within the MUGA.

Layers Relative to the Municipal Urban Growth Area

Each geoprocessed layer gives a complex explanation to the change in land cover within the watershed.  Since the depth of this project is limited based upon the time allotted for this quarter, categories needed to be simplified and grouped together in a way that was manageable.  The outputs do give some good indicators as to where land cover has changed and how this is relative to new urban growth.  Since studies on urban growth in this format have not really been executed before it’s hard to compare my findings to those in other studies.  Also, data restrictions have confined this study to a certain time frame.  I wish that follow-up studies with recent data (or pre 1990 data) could be executed in the same process as mine as to show differences between decades.  Also, data limitations provide a lot of room for error as population data doesn’t line up in the same time frame as land cover changes.  Nonetheless, we can make some basic assumptions that the changes within these time periods are substantial and have social and environmental costs that need to be accounted for so that future costs are manageable and controlled.

The Puget Sound region has seen a large net inflow of migrants as well as natural increases.  Net migration, people moving in minus people moving out, and natural increase, births minus deaths, has varied over time.  Between 1960 and 2006 net migration accounted for 56% of the Puget Sound region’s growth and natural increase accounted for 44% of the region’s growth.  Total increase in this time was approximately 2 million people (PS trends).  Net migration depends primarily on economic health and job opportunities.  As the Snohomish watershed lies along outskirts of the Puget Sound metropolitan cities and suburban areas, it is understandable that much of the new population increases are occurring on city outskirts and in the watershed. 

The Growth Management act of the Puget Sound had a goal to keep the majority of population increase within the MUGA.  I originally hypothesized that most population increase would be in the outer suburban areas outside of the MUGA.  My findings show that 75.3% of new population increase has occurred within the MUGA area.  This population growth has certain implications on land cover impacts.  I estimate that this reinforces positive management since these are people have less of a new impact on land cover.

Land Cover changes inside the MUGA were 35.5% of the total land cover change.  This percent of change is what I expected as most land in the MUGA has already been transformed from natural land cover to a developed state.  Still, 22,480 new inhabitants outside of the MUGA can be compared to the 18.9 square miles of land cover change.  That is 0.58 acres of land cover change per capita outside the MUGA.  This comparison shows only the proportional difference of per capita land cover change outside the MUGA (0.58 acres per capita) relative to the whole (0.21 acres per capita).  We can’t assume that inhabitants outside the MUGA are the only contributing factor to the land cover change outside the MUGA.  The reclassification of land cover types may also explain the high area of new developed land outside the MUGA as all agricultural land was included in developed land.  But, we must remember that agricultural land is still developed land with just as negative of impacts on the environment.

Impervious surface increases in the watershed were 57.6% within the MUGA.  Looking at impervious surfaces and its implications we can see that any new impervious, surface no matter where, is going to have negative impacts on the fluvial processes that occur.  Peak runoff during peak flows is going to higher and greater amounts of toxins and chemicals are going to be flushed into stream flows.  So based on whether impervious surfaces are increasing in the MUGA or not, I hypothesize that the negative environmental impacts are equal.

As far as canopy cover loss goes, I don’t see a connection to urban growth.  Most canopy cover loss occurred outside the MUGA in logging areas.  I believe that this layer reinforces the fact that land cover is changing, but should not be focused on for relations to urban growth.

In conclusion, I accept my hypothesis that the majority of land cover change from natural to developed land is occurring outside the MUGA.  I reject my hypothesis that the majority population increase in the watershed occurred outside the MUGA.  These are rudimentary findings based upon the amount of detail that could go into this study.  Population change and land cover changes are complex transitions that take in a handful of detailed factors that I did not even touch on.  But, for the extent of my study, the layers created give a good assessment for how urban sprawl is exceeding the MUGA and give a good forecast of how current trends could lead to future land management issues in trying to protect the health of the watershed as a whole.

Sources:

Population change and net migration. (2008). Puget Sound Trends, (7), Retrieved from http://psrc.org/data/trends/

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