Abstract
It is important to understand the distribution of irrigated and non-irrigated vegetation in rapidly expanding urban areas that are experiencing climate-induced changes in water availability, such as Los Angeles, California. Mapping irrigated vegetation in Los Angeles is necessary for developing sustainable water use practices and accurately accounting for the megacity’s carbon exchange and water balance changes. However, pre-existing maps of irrigated vegetation are largely limited to agricultural regions and are too coarse to resolve heterogeneous urban landscapes. Previous research suggests that irrigation has a strong cooling effect on vegetation, especially in semi-arid environments. The July 2018 launch of the ECOsystem Spaceborne Thermal Radiometer on Space Station (ECOSTRESS) offers an opportunity to test this hypothesis using retrieved land surface temperature (LST) data in complex, heterogeneous urban/non-urban environments. In this study, we leverage Landsat 8 optical imagery and 30 m sharpened afternoon summertime ECOSTRESS LST, then apply very high-resolution (0.6–10 m) vegetation fraction weighting to produce a map of irrigated and non-irrigated vegetation in Los Angeles. This classification was compared to other classifications using different combinations of sensors in order to offer a preliminary accuracy and uncertainty assessment. This approach verifies that ECOSTRESS LST data provides an accurate map (98.2% accuracy) of irrigated urban vegetation in southern California that has the potential to reduce uncertainties in regional carbon and hydrological cycle models.
Highlights
Urban areas are expanding rapidly across the world and currently comprise 54% of the global population, versus 30% in 1950 [1]
Irrigation and water use patterns are highly complex in heterogeneous urban areas like the southern California Air Basin (SoCAB)
Previous efforts to classify land use in irrigated areas have typically focused on agricultural regions, which consist of relatively large fields spanning hundreds of hectares, cover a large portion of the United States and other nations, and can account for the majority of freshwater use
Summary
Urban areas are expanding rapidly across the world and currently comprise 54% of the global population, versus 30% in 1950 [1]. A growing field of research suggests that irrigation has a strong cooling effect on vegetation that is most pronounced in semi-arid and arid climates and can be measured using remotely sensed land surface temperature (LST) [12,13]. Previous efforts to classify land use in irrigated areas have typically focused on agricultural regions, which consist of relatively large fields spanning hundreds of hectares, cover a large portion of the United States and other nations, and can account for the majority of freshwater use. Chance et al (2017) used Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat 5 optical imagery to distinguish between irrigated and non-irrigated land in the semi-arid agricultural Snake River Plain in Idaho with accuracies varying from 86% to 95% depending on the sensor and spectral vegetation index used. Twhoerwkfolrokwflofowr fsourpseurpveisrevdisecldascslaifsisciafiticoantioton dtoisdtiinstginugisuhisbhetbweteweneeinrriirgraigteadteadnadndnonno-nir-riirgriagtaetdedsescetciotinonis isbrborkoekneninitnotothtrheereme aminaisnecsteicotniosn(sFi(gFuigreur1e).1T).raTinrianingindgatadastealescetlieocntiiosnadisdaredsdsreedssiendSienctSioenct2io.5n, a2n.5d, acnladscsliafisesrifitrearintrianignianngdavnadlivdaaltiidoantiaorne aardedardesdsreedssiendSienctSieocnti2o.n6.2.6
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