Knowledge of how urban environments impact precipitation will have implications for how urban areas are represented in future generations of weather and climate models; how urban planners and water resource managers plan cities; how agricultural activities carried out; and numerous other societal benefit applications. Algorithm development, ground validation, and modeling are vital research areas, but it is increasingly important that the NASA Precipitation Science Team represent research tracks addressing applications and implications of precipitation variability to weather, climate, and hydrology.
In a recent report to the National Academy of Sciences and Senior Review Panel at NASA (TRMM, 2005), the need for extended TRMM observations (and future GPM observations) were placed in the context of current and emerging science questions. The role of human activities (e.g. aerosols and urbanization) in precipitation-related processes was prominently highlighted in the report. Our proposed research program is consistent with the Academy report recommendations, addresses NASA Precipitation Science program elements and enables us to leverage the extended dataset of TRMM while preparing for the GPM era. Here, we describe our science objectives and their linkages to the objectives (for example, objective 1.1 and 1.3) listed in the NASA Research Announcement.
Precipitation Variability and its Relationship to Climate Diagnostics and Change:
Objective 1: We will analyze 3-hourly TRMM daily and merged product data cross-referenced with rain gauge rainfall measurements for a cross-section of U.S. and global cities to perform a national and global climate assessment of urban effects on precipitation. This effort will focus on identifying influencing factors (geography, aerosols, climate, terrain, coastal effects, etc.) and establishing the presence of an ""urban climate signal"" in precipitation variability
Objective 2: We will use TRMM, MODIS, and emerging cloud satellite data to investigate the relative role of urban aerosol-microphysics and urban-induced dynamics on precipitation variability and regional climates and then test our hypotheses using a newly introduced aerosol parameterizations in a climate version of the WRF regional model (with advanced urban parameterization).
Objective 3: Using projected urban growth scenarios for selected urban areas; we will assess the impact of future urban land use and aerosol loads on regional climates, in terms of precipitation variability and surface hydrologic response (e.g., runoff, evapotranspiration).
Applications to Hydrology and Oceanography:
Objective 4: We will continue to develop a regional-to-urban scale distributed hydrologic model. We will develop a technique to link TRMM-based merged 3-hour and 1-hour rainfall observations to the multi-scale model and define the pathway for similar applications using GPM data. A downscaling approach will be developed to correctly scale the TRMM-based Merged Products to the spatial resolution necessary to drive a regional distributed hydrologic model and an urban flood prediction model.
Objective 5: We will use space-based precipitation datasets to assess urban water sustainability. First, an approach integrating remote sensing and ancillary geospatial datasets will be developed to define the spatial extent (including imported water sources) of the urban hydrologic influence, which we will term the urban hydrologic footprint. We will then quantify the fluxes of water to and from the hydrologic footprint, determine the stores as residuals, and estimate residence times from flux time series. The study will uniquely incorporate remote sensing precipitation and land surface observation datasets into short-term urban water planning and reduce the uncertainty associated with spatial distribution of estimates of precipitation fluxes and consumptive uses at the urban water budget scale.
