Urban Irrigated Vegetation Mapping in Los Angeles, California with ECOSTRESS Imagery

Abstract:

Understanding the distribution of irrigated and non-irrigated vegetation in rapidly expanding urban areas that are experiencing climate-induced changes in water availability (e.g., Los Angeles), is necessary for developing sustainable water use practices. To do so, we must identify urban irrigated land use patterns needed to accurately model local and regional carbon and hydrological cycles. However, irrigation and water use patterns are challenging to map in complex, heterogeneous urban areas like Los Angeles, where vegetation in the urban core consists of small landscaped parcels interspersed with turfgrass and non-native trees, while non-urban areas are characterized by steep terrain and a combination of Mediterranean chaparral and evergreen forest. Pre-existing maps of irrigated vegetation are largely limited to non-urban agricultural regions and are too coarse to improve understanding of carbon and water cycles in urban regions.

Previous research suggests that irrigation has a strong cooling effect on vegetation land surface temperature (LST), especially in semi-arid environments, and the recent launch (July 2018) of the moderate-resolution (70-100 m, 3-5 day revisit) ECOsystem Spaceborne Thermal Radiometer on Space Station (ECOSTRESS) offers an opportunity to test this hypothesis in such complex, heterogeneous urban environments. We will demonstrate the feasibility of classifying irrigated versus non-irrigated vegetation with vegetation-fraction weighted LST across urban and non-urban areas of southern California. We weighted 30 m sharpened afternoon summertime ECOSTRESS LST with a high-resolution (0.6-10 m) vegetation classification map to produce a map of irrigated versus non-irrigated vegetation in Los Angeles with 98% accuracy. We compare this classification to classifications with other sensors and offer a preliminary accuracy and uncertainty assessment. This approach verifies the use of ECOSTRESS in urban/non-urban environments, will help resolve uncertainties in regional carbon and hydrological cycle models, and provides a map of irrigated urban vegetation in Los Angeles and the southern California Air Basin (SoCAB).