Take Home Message

Model results show a loss of agricultural lands in the valley as cities expand throughout the 21st century.  This loss of farmland causes a slight decline in water demand for agricultural irrigation, despite the warming climate.  Two alternative scenarios explore the effect of increasing the population growth rate and reducing the density of future urban development.  Both factors accelerate the loss of farmland in model results.

Key Findings

Background

The Relaxed Urban Expansion (UrbExpand) scenario allows cities to expand with lower density development. Specifically, cities will expand their Urban Growth Boundary when 70% of the lands within the Urban Growth Boundary are developed. This contrasts with the Reference scenario which sets this threshold to 80%. In UrbExpand , growth of the Portland Metro UGB is not constrained to urban reserves as it is in the Reference scenario through 2060.

The Data

Below we compare the Reference and Relaxed Urban Expansion scenarios. For comparison, we also include results for the High Population scenario in some charts.

First, we look at the conversion of agricultural lands to urban uses in these scenarios.

Frequency of Conversions from Agriculture to Developed
Land Use/Land Cover Trends

Next, we look at the water demand story for municipal and agricultural uses for each scenario. Water consumption for agricultural irrigation is projected to decline slightly by the end of the century, while municipal uses increase in response to population growth, largely occuring in urban areas.

Water Demand Summary, Irrigated Ag and Municipal, across the three scenarios



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