Ongoing NASA Efforts Addressing precipitation variability linked to the urban environment

Urbanization is one of the extreme cases of land use change. Most of world’s population has moved to urban areas. Although currently only 1.2% of the land is considered urban, the spatial coverage and density of cities are expected to rapidly increase in the near future. It is estimated that by the year 2025, 60% of the world’s population will live in cities. Human activity in urban environments also alters weather and climate processes. However, our understanding of urbanization on the total Earth-weather-climate system is incomplete. Recent literature continues to provide evidence that anomalies in precipitation exist over and downwind of major cities. Current and future research efforts are actively seeking to verify these literature findings and understand potential cause-effect relationships.

Ongoing NASA-sponsored research is exploring the linkage between the urban environment and precipitation variability. At this meeting, we provide an overview of multiple activities aimed at addressing this problem. First, we identify temporal and spatial “urban-rainfall anomalies” around global cities using data from multiple satellite data sources (e.g. TRMM precipitation radar, TRMM-geosynchronous-rain gauge merged product, and SSM/I) and ground-based measurements. Second, we discuss results from preliminary MM5 model experiments coupled to three land surface models (SLAB, NOAH, and Goddard PLACE). These results clearly indicate the impact of complex urban land surfaces on the morphology of precipitation. The results also suggest a need for improved representation of urban surfaces in these types of coupled experiments and larger scale models (e.g. GCMs). Third, we provide an overview of the Studies of PRecipitation Anomalies from Widespread urban Landuse (SPRAWL) experiment being conducted during August-September 2005 in Atlanta. Furthermore, important and an unsolved science problems being addressed by our team are to understand and identify the relative importance of urban-induced convergence, urban boundary layer destabilization, or urban aerosols on precipitation morphology, spatial distribution, and diurnal trends.

This research is conducted within the context of NASA efforts to understand how weather, climate, and the water cycle are impacted by the natural and human-induced activity. The research also has implications societal areas related to weather forecasting, agriculture, disaster management, and water resource management.