Estimating trends of urban residential irrigation extent and rate using satellite imagery in the city of Los Angeles, CA

Abstract:

Urban residential irrigation is a large component of urban water budgets in Mediterranean climate cities, and plays a significant role for managing landscape vegetation and water resources. This is particularly occurring at cities such as Los Angeles, where water availability is limited during dry summers. This study applied 10-m SPOT 5 satellite imagery and a database of monthly water use records for residential water customers in Los Angeles in order to examine the interactions between vegetation water demand and residential water consumption. Here, we identify the spatial distribution of vegetation greenness and the extent of irrigation rates through water year 2005-2007, including normal, dry, and wet extremes of annual rainfall. Additionally, the water conservation ratio, which is between rates of irrigation and vegetation water demand, is used to assess over-irrigation. Although residential outdoor water usage was found as highest in the dry year, landscape vegetation under water stress that cannot maintain greenness condition as well as in wetter years. However, the decreasing trend of over-irrigation occurred from wet to drier years, since vegetation water demand increased significantly but irrigation rates changed little, implying over-irrigation in urbanized areas. This over watering issue can be implemented by water resource management, and urban planning, especially in current severe California drought.