102 Brindal and Stringer: Water Scarcity and Urban Forests Arboriculture & Urban Forestry 2013. 39(3): 102–108 Water Scarcity and Urban Forests: Science and Public Policy Lessons from a Decade of Drought in Adelaide, Australia Mark Brindal and Randy Stringer Abstract. Drawing on the experience of greater metropolitan Adelaide, South Australia, Australia, the paper points to the links and gaps between science and public policy. The paper explores urban stormwater management lessons emerging from a ten-year, prolonged dry period that impacted the integrity of urban forests in the City of Adelaide. Among the questions addressed: will stormwater remain, as its historic and institutional settings suggest, a liabili- ty or can it become an asset? Who owns stormwater resources and to whom is its management vested? The paper examines these issues with consideration to the dangers of continuing to use urban forestry management practices that are not informed by science. The study concludes that a more integrated ap- proach to urban water management can maintain the integrity of urban forests in ways that potentially enhance social amenities and economic efficiency. Key Words. Adelaide; Australia; Stormwater; Urban Forest Management; Water Policy. In the urban environment, trees are forced to compete for their water with the conflicting demands of the urban built form: vast areas of impermeable surface and drainage infra- structure designed, traditionally, to ensure that precipitation run-off is expeditiously and efficiently removed. Where they exist, the narrow verges through which street trees are supposed to obtain their water are too often inadequate for that purpose (Connellan 2008; May 2009). A number of studies present valuable evidence as to why this occurs (Whitlow et al. 1992; Wagar and Franklin 1994; Morgenroth and Buchan 2009). In Adelaide, South Australia, Australia, with an average annu- al precipitation of less than 600 mm, the urban forest, and in par- ticular street trees, prosper. In recent years, Adelaide’s urban for- ests have faced significant challenges from a ten-year, prolonged dry period (PDP), spanning November 2001 until March 2010. Several key developments during the PDP suggest that the urban forest and street trees are unlikely to maintain their health. First, natural underground water resources provide sustenance for some of the city’s street trees, leaky potable water, and sewerage infra- structure for many others. For the most part, it is the proximity to the city’s well-watered greenspaces (most of which are privately owned) that contribute to the health of the street tree component of Adelaide’s urban forest. However, during the PDP all households were subjected to water restrictions, greatly reducing the amount of water applied to gardens (Government of South Australia 2011). Second, two recently released government program initia- tives require changes to how street trees are managed. The ‘30 Year Plan for Greater Adelaide’ (Government of South Austra- lia 2010) and ‘Water for Good’ (Government of South Austra- lia 2009) programs aim to integrate policy for stormwater and urban forest management. The private and public incentives created by each program impact the viability of urban greens- paces. For example, the 30 Year Plan controls urban sprawl by ©2013 International Society of Arboriculture pursuing urban infill, with potential negative consequences for how impermeable surface areas impact the ability of the urban forest to receive its water requirement through natural absorption. The Water for Good program enshrines a target for the har- vesting of 60 GL of stormwater a year by 2050 to ensure the ongoing viability of the city’s potable water supplies. One recent study estimates that urbanized areas in the region pro- duce about 86 GL of stormwater run-off per annum (Govern- ment of South Australia 2009). At present, most stormwater flows into the gulf to the west. The volume targeted for col- lection represents approximately two-thirds of the total esti- mated urban run-off (Government of South Australia 2004a). The third development impacting street trees is propos- als to reduce leakage in both the potable water and sewerage systems, further depriving the urban forest of water. Because of the water restrictions implemented during the PDP, the sub- urbs of Adelaide present many examples of abandoned gardens. Some households installed water-wise plants or subsurface irrigation, while others increased areas of impermeable paved surface. Some of these actions may deprive plants of moisture. Drawing on the experience of greater metropolitan Ade- laide during the PDP, this paper aims to highlight the links and gaps between science and public policy that inhibit the capac- ity to organize more effective institutional structures to manage water for trees. In Adelaide’s case, urban stormwater manage- ment is the core issue. The paper examines whether the recent experience with stormwater events reveal the city’s current in- stitutional arrangements as more of an asset or liability. Why are the tradeoffs of how storm water is managed and used not considered? Who owns storm water, in whom is its management vested and does its management impact the urban forest? This paper seeks to explore these questions, examining the risks for Adelaide’s urban forest. It concludes that through a more holis-
May 2013
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