Urban outdoor water use and response to drought assessed through mobile energy balance and vegetation greenness measurements

Authors: LIANG, LLYIN - University Of Waikato; Anderson, Raymond - Ray; SHIFLETT, SHERI - University Of California; JENERETTE, DARREL - University Of California

Submitted to: Environmental Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2017
Publication Date: 7/28/2017
Publication URL: https://handle.nal.usda.gov/10113/5801794
Citation: Liang, L.L., Anderson, R.G., Shiflett, S.A., Jenerette, D.G. 2017. Urban outdoor water use and response to drought assessed through mobile energy balance and vegetation greenness measurements. Environmental Research Letters. 12:084007. doi: 10.1088/1748-9326/aa7b21.

Interpretive Summary: Agricultural and urban irrigation has is a major consumptive use of water, primarily through evapotranspiration. Irrigation sources in California are severely stressed due to drought and environmental preservation requirements. Measuring evapotranspiration at high spatial scales in urban and mixed agricultural/urban areas is critical for assessing strategies to conserve water and for observing water reduction mandates. However, current methods for spatial measurement of agricultural evapotranspiration cannot be used in urban and mixed agricultural and urban areas due to presence of streets and buildings. In this study, we combine surface measurements of evapotranspiration and evaporative fraction with satellite measurements of vegetation greenness and net radiation to observe evapotranspiration across Riverside, California at high spatial resolution. The results show that combining mobile surface meteorological measurements with satellite resolution can assess changes in evapotranspiration in response to policies designed to reduce irrigation in urban areas (primarily in response to water reduction mandates following the Southern California drought of 2012-present). The research benefits policymakers and water managers who want to assess methods to reduce outdoor consumptive use in urban areas, which may reduce current and future competition with agricultural irrigation needs.

Technical Abstract: Urban vegetation provides many highly valued ecosystem services but also requires extensive urban water resources. Increasingly, cities are experiencing water limitations and managing outdoor urban water use is an important concern. Quantifying the water lost via evapotranspiration (ET) is critical for urban water management and conservation, especially in arid or semi-arid regions. In this study, we deployed a mobile energy balance platform to measure evaporative fraction throughout Riverside, California, a warm, semi-arid, city. We observed the relationship between evaporative fraction and satellite derived vegetation index across 29 sites, which was then used to map whole-city ET for a representative mid-summer period. Resulting ET distributions were strongly associated with both neighborhood population density and income. By comparing 2014 and 2015 summer-period water uses, our results show 7.8% reductions in evapotranspiration, which were also correlated with neighborhood demographic characteristics. Our findings suggest a mobile energy balance measurement platform coupled with satellite imagery could serve as an effective tool in assessing the outdoor water use at neighborhood to whole city scales.