Shifting landscapes: decoupled urban irrigation and greenness patterns during severe drought

Abstract

Urban outdoor water conservation and efficiency offer high potential for demand-side management, but irrigation, greenness, and climate interlinks must be better understood to design optimal policies. To identify paired transitions during drought, we matched parcel-level water use data from smart, dedicated irrigation meters with high-spatial resolution, multispectral aerial imagery. We examined changes across 72 non-residential parcels using potable or recycled water for large landscape irrigation over four biennial summers (2010, 2012, 2014, and 2016) that encompassed a historic drought in California. We found that despite little change in irrigation levels during the first few years of the drought, parcel greenness deteriorated. Between summers 2010 and 2014, average parcel greenness decreased −61% for potable water irrigators and −56% for recycled water irrigators, providing evidence that vegetation could not reach its vigor from wetter, cooler years as the drought intensified with abnormally high temperatures. Between summers 2014-2016 as drought severity lessened, irrigation rates decreased significantly in line with high drought saliency, but greenness rebounded ubiquitously, on average +110% for potable water irrigators and +62% for recycled water irrigators, demonstrating climate-driven vegetation recovery as evaporation and plant evapotranspiration rates decreased. Transitions were similar for customers with both potable and recycled water; vegetation changes were dominated by the overarching climatic regime. As irrigation cannot always overcome drought conditions, which will become more severe under climate change, to maintain vegetation health, utilities and urban planners should consider the tradeoffs between providing green spaces and water scarcity. This includes evaluating the roles of climate-appropriate landscaping and adaptive reallocation of potable and recycled water resources to enhance water security. By addressing emerging themes in urban water management through analysis of data from forthcoming water metering and aerial imagery technologies, this research provides a unique perspective on water use, greenness, and drought linkages.

Satellites to Sprinklers: Assessing the Role of Climate and Land Cover Change on Patterns of Urban Outdoor Water Use

“…(2012) identify a 1.4% increase in water consumption for every 1°F increase in nighttime temperature in Phoenix, Arizona, highlighting the importance of feedbacks between the built environment and urban vegetation. However, recent studies have shown that during drought, urban irrigation and greenness can become decoupled, and increases in irrigation do not result in maintained vegetation greenness through the duration of a drought for any vegetation type (Miller et al., 2020; Quesnel et al., 2019). Because vegetation responds most strongly to climate signals, increased outdoor water use in a hotter climate is unlikely to maintain verdant, lush vegetation, prompting continued overapplication of urban irrigation or adaptation of urban vegetation regimes.…”

“…Estimates of outdoor water use remain largely uncertain due to inconsistent calculation methods, lack of metering, and limited data (Anda et al., 2013; Boyle et al., 2013; Gleick et al., 2003). Dual metering, with dedicated irrigation meters, is becoming a more common practice and a promising component of outdoor water use evaluations and conservation management (Quesnel & Ajami, 2019; Quesnel et al., 2019). However, implementation of dual metering is limited in scope and often excludes single‐family residential properties.…”

“…Until dual metering is more common, water management must rely on alternate methods to evaluate and manage outdoor use. Remote sensing data provide a means of monitoring changes in landscape dynamics with frequent, spatially distributed observations (Atasoy, 2018; Fan et al., 2017; Kar et al., 2018; Quesnel et al., 2019; Rango, 1994). Boegh et al.…”

Curbing the Summer Surge: Permanent Outdoor Water Use Restrictions in Humid and Semiarid Cities

“…Outdoor water use is more elastic and discretionary than other water use categories and can theoretically be curtailed rapidly in response to climate signals (Breyer et al, 2018; Espey et al, 1997; Lyman, 1992). Fresh findings also suggest that reducing the use of city water outdoors need not come at a high environmental cost: Research from California suggests that the health of urban greenspaces is largely decoupled from irrigation water use during drought episodes and that the greenness of those landscapes can rebound rapidly once the rains return (Quesnel et al, 2019). Turfgrass species commonly used in urban landscaping are especially adept at surviving summer drought stresses, so reducing irrigation of urban greenspaces during periods of low water availability can potentially be achieved without sacrificing their long‐term health (Beard & Green, 1994).…”

Quantifying the Multiplier Effect of Southern California’s Turf Removal Rebate Program with Time‐Series Aerial Imagery

“…The value of a time‐series analysis of multispectral imagery to characterize vegetation is recognized by the United States (U.S.) Department of Agriculture’s National Agricultural Imagery Program (NAIP), which collects nationwide, multispectral imagery every two years during the late summer since 2003 (Grant 2018). More recently, time‐series analysis of NAIP imagery has been used to delineate natural from artificial turf and track changes to natural turf vigor as a result of decreased irrigation (Quesnel et al 2019).…”