Abstract
Economic growth in Central Arizona, as in other semiarid systems characterized by low and variable rainfall, has historically depended on the effectiveness of strategies to manage water supply risks. Traditionally, the management of supply risks includes three elements: hard infrastructures, landscape management within the watershed, and a supporting set of institutions of which water markets are frequently the most important. In this paper we model the interactions between these elements. A forest restoration initiative in Central Arizona (the Four Forest Restoration Initiative, or 4FRI) will result in thinning of ponderosa pine forests in the upper watershed, with potential implications for both sedimentation rates and water delivery to reservoirs. Specifically, we model the net effect of ponderosa pine forest thinning across the Salt and Verde River watersheds on the reliability and cost of water supply to the Phoenix metropolitan area. We conclude that the sediment impacts of forest thinning (up to 50% of canopy cover) are unlikely to compromise the reliability of the reservoir system while thinning has the potential to increase annual water supply by 8%. This represents an estimated net present value of surface water storage of $104 million, considering both water consumption and hydropower generation.
Highlights
At the close of the first decade of this century, a special issue of the Proceedings of the National Academy of Sciences painted a grim picture of the sustainability of future water supplies in the American Southwest [1]
To estimate the impact of a change in land cover on water and sediment yields, and water costs, we considered the effect of an arbitrary change in canopy cover in the ponderosa pine forest that occupies the upper part of Salt and Verde watersheds
We restricted ourselves to ponderosa pine forest, but instead of a 50% reduction in basal area, we considered a reduction to 50% canopy cover
Summary
At the close of the first decade of this century, a special issue of the Proceedings of the National Academy of Sciences painted a grim picture of the sustainability of future water supplies in the American Southwest [1]. The region is expected to experience declining winter precipitation and increasingly severe and prolonged droughts over the 21st century. During this period, drought episodes (typified by continuous soil moisture depletion) are expected to increase from 4–10 years to periods of 12 years or more [2, 3]. At the same time, continued population growth is expected to increase demand for water, leading to PLOS ONE | DOI:10.1371/journal.pone.0121596. At the same time, continued population growth is expected to increase demand for water, leading to PLOS ONE | DOI:10.1371/journal.pone.0121596 April 2, 2015
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