Spatiotemporal Structure of Tropical Moisture Exports and their Precursors associated with High Precipitation induced Floods over the Continental United States

Friday, 19 December 2014
Mengqian Lu, Columbia University of New York, Palisades, NY, United States and Upmanu Lall, Columbia Univ, New York, NY, United States
Nonstationarity of flood risk has emerged as an important issue and progress in addressing this concern can only come from an improved understanding of the associated climate dynamics. An understanding of the dynamical mechanisms and statistics associated with the frequency and structure of heavy precipitation induced floods events can aid exploration of the key sources of uncertainties that challenge extreme hydrometerological forecasts, and improve reliability of streamflow forecasts for real-time applications.

Although the climate mechanisms governing precipitation vary by location, extreme precipitation events in the mid-latitudes are typically associated with anomalous atmospheric moisture from warmer tropical or subtropical oceanic areas. Tropical moisture exports (TMEs) to the Northern Hemispheric extratropics are an important feature of the general circulation of the atmosphere and link tropical moisture sources with extratropical precipitation and occasionally with explosive cyclogenesis. TMEs, contributing to the global climatology precipitation and its extremes, are closely related to flood events, especially in the midlatitudes.

Here, a statistically and physically based framework is put forward that investigates the relationship between TMEs, and Extreme Precipitation and Floods over the continental United States, and relates the spatial flood incidence across the regions to the persistence and spatiotemporal structure of these tracks. The origins and pathways of moist and warm tropical air masses, which are the fuel for the heavy precipitation events and rapid cyclogenesis in the extratropics, are examined. The clustered TME tracks provide a critical source of identify different moisture sources and climate dynamics, which governs and drives the movements of water vapor to the flooded areas, together with an atmospheric circulation pattern that leads to persistent multi-day convergence and precipitation in those regions. The genesis location of TME can be linked to the seasonality and sea surface temperature; while the variance or the second moments of the tracks recognize the water vapor contents and most importantly monitor the lease of the moisture, which may directly induces intensive precipitation, that are potentially attributable for flooding events followed.