Urbanization diversifies land surface phenology in arid environments: Interactions among vegetation, climatic variation, and land use pattern in the Phoenix metropolitan region, USA

Urbanization transforms vegetation pattern and ecosystem processes which are controlled primarily by climate in desert regions. The objective of this study was to investigate how urbanization affects vegetation phenology and its coupling with climate in the Phoenix metropolitan region, USA. Our analysis of Normalized Difference Vegetation Index (NDVI) time-series reveals a complex pattern of land surface phenology in response to urbanization. Croplands and urbanized areas show growth multimodality, which is usually found in riparian areas of the region but absent in the native desert. Agriculture is characterized by the shortest growth length and fastest greening and senescing rates. Conversely, urban vegetation stays photosynthetically active for longer periods. Desert NDVI is regulated by 3-5 month accumulated precipitation, but riparian vegetation is uncorrelated with rainfall. NDVI spatial patterns are best predicted by climatic variables near the peak of annual growth. Spring and summer NDVI is in better agreement with precipitation accumulated over longer time periods, while early autumn growth is strongly correlated with immediate and one-month rainfall. Temperature correlates negatively with desert but positively with riparian NDVI. Managed vegetation growth is decoupled from precipitation and completely unsynchronized with natural desert vegetation. Overall, urbanization has resulted in a greater phenological diversity that is not in sync with climatic variability. Our findings provide new insights into the interactions among vegetation growth, climate variability, and urbanization in dry lands.