The impacts of a warming climate on the global hydrological cycle have been examined extensively since the publication of the First Assessment Report by the Intergovernmental Panel on Climate Change (1993) (IPCC). Climate model projections point to increases in extreme rainfall as a result of an intensified hydrological cycle (e.g.,

The Lower Mississippi River has experienced a cluster of extreme floods during the past two decades. The Bonnet Carré spillway, which is located on the Mississippi River immediately upstream of New Orleans, has been operated 15 times since its completion in 1931, with 7 occurrences after 2008. In this study, we examine rainfall and atmospheric water balance components associated with Lower Mississippi River flooding in 2008, 2011, 2015-2016, 2017, 2018, and 2019. We focus on multiple time scales - 1, 3, 7, and 14 days - reflecting contributions from individual storm systems and the aggregate contributions from a sequence of storm systems. Atmospheric water balance variables - integrated water vapor flux (IVT) and precipitable water - are central to our assessment of the storm environment for Lower Mississippi flood events. We find anomalously large IVT corridors accompany the critical periods of heavy rainfall and are organized in southwest-to-northeast orientation over the Mississippi domain. Atmospheric Rivers play an important role as agents of extremes in water vapor flux and rainfall. We conduct climatological analyses of IVT and precipitable water extremes across the four time scales using 40 years of North American Regional Reanalysis (NARR) fields from 1979 to 2018. We find significant increasing trends in both variables at all time scales. Increases in IVT especially cover large regions of the Mississippi domain. The findings point to increased vulnerability faced by the Mississippi flood control system in the current and future climate.

On 1 September 2021, the remnants of Hurricane Ida transformed into a lethal variant of tropical cyclone in which unprecedented short‐duration rainfall from clusters of supercells produced catastrophic flooding in watersheds of the Northeastern US. Short‐duration rainfall extremes from Ida are examined through analyses of polarimetric radar fields and rain gauge observations. Rainfall estimates are constructed from a polarimetric rainfall algorithm that is grounded in specific differential phase shift (KDP) fields. Rainfall accumulations at multiple locations exceed 1000‐year values for 1–3 hr time scales. Radar observations show that supercells are the principal agents of rainfall extremes. Record flood peaks occurred throughout the eastern Pennsylvania—New Jersey region; the peak discharge of the Elizabeth River is one of the most extreme in the eastern US, based on the ratio of the peak discharge to the sample 10‐year flood at the gaging station. As with other tropical cyclones that have produced record flooding in the Northeastern US, Extratropical Transition was a key element of extreme rainfall and flooding from Ida. Tropical and extratropical elements of the storm system contributed to extremes of atmospheric water balance variables and Convective Available Potential Energy, providing the environment for extreme short‐duration rainfall from supercells.

Extreme rainfall from extratropical cyclones and the distinctive hydrology of the winter season both contribute to flood extremes in the Mid-Atlantic region. In this study, we examine extreme rainfall and flooding from a winter season extratropical cyclone that passed through the eastern U.S. on 24-25 February 2016. Extreme rainfall rates during the 24-25 February 2016 time period were produced by supercell thunderstorms; we identify supercells through local maxima in azimuthal shear fields computed from Doppler velocity measurements from WSR-88D radars. Rainfall rates approaching 250 mm h−1 from a long-lived supercell in New Jersey were measured by a Parsivel disdrometer. A distinctive element of the storm environment for the 24-25 February 2016 storm was elevated values of Convective Available Potential Energy (CAPE). We also examine the climatology of atmospheric rivers (ARs) - like the February 2016 storm - based on an identification and tracking algorithm that uses 20th Century Reanalysis fields for the 66 year period from 1950 - 2015. Climatological analyses suggest that AR frequency is increasing over the Mid-Atlantic region. An increase in AR frequency, combined with increasing frequency of elevated CAPE during the winter season over the Mid-Atlantic region could result in striking changes to the climatology of extreme floods.

In the agricultural state of Iowa, water quality research is of great importance for monitoring and managing aquatic systems health. Among many water quality parameters, water temperature is a critical variable that governs the rates of chemical and biological processes which affect river health. A statistical model was developed to produce realtime high resolution predictive stream temperature for the entire state of Iowa. The implemented model generates current-hour stream temperature estimations statewide. Forecasts for 18 hours in advance are also available. The hourly estimation results are updated in real-time and presented on a web-based visualization platform: the Iowa Water Quality Information System, Beta version (IWQIS Beta). This product will assist Iowa water quality research and provide information to support public management decisions. v TABLE OF CONTENTS LIST OF TABLES .