Title: Stochastic Storm Transposition using HEC-HMS

Speaker: Greg Karlovits, Acting Chief of the Hydrology and Statistics Division at the USACE Hydrologic Engineering Center

Description: HEC has been enhancing several of its software programs in support of the FEMA Future of Flood Risk Data Initiative. In the past couple of years, HEC-HMS has added capability to transpose gridded precipitation fields for hydrologic simulation, and to use uncertainty analysis and optimization techniques to transpose these storms in a targeted way. Stochastic Storm Transposition (SST) is a technique for analyzing watershed-average precipitation-frequency and flow-frequency throughout a watershed, and this presentation will highlight how new capabilities in HEC-HMS can be used to perform SST simulations.

Title: Process-Based Quantification of the Role of Wildfire in Shaping Flood Frequency

Speaker: Dr. Guo Yu, Assistant Research Professor, Desert Research Institute

Description: Moderate to high severity wildfire can abruptly alter watershed properties and enhance extreme hydrologic responses such as debris flows and floods. The compounding effects of wildfire on flood hazard, represented here via flood frequency analysis (FFA; e.g., 100-year flood) are of growing importance. Standard statistical FFA approaches are ill-suited to examining this issue because wildfire-affected flood peak observations are limited in number and violate the assumption of independent and identically distributed events. Here, we developed a process-based FFA framework that integrates a stochastic rainfall generator, wildfire simulation, inverse modeling, and a physics-based hydrological model to directly simulate the impacts of wildfire on FFA. We applied this framework in the upper Arroyo Seco watershed in Southern California.

Title: Surface Hydrology Research in Agricultural Watersheds in South Brazil

Speaker: Alice Dambroz, PhD student in Soil Science at Universidade Federal de Santa Maria, in Brazil

Description: For over twenty years, agricultural watersheds have been hydrologically monitored in South Brazil. These monitoring projects seek to quantify and understand the impact of agricultural activities on processes related to surface hydrology and soil erosion. These watersheds represent different scales, geomorphological characteristics, and land uses. They are also used as experimental watersheds for the purposes of teaching and training students and future researchers in environmental monitoring and modelling. In Arvorezinha, a 1 km2 watershed on the edge of a volcanic plateau has had tobacco, forest, and grain cultivation. Conceição is an 800 km2 watershed and, in Júlio de Castilhos, hillslopes and paired zero-order catchments represent the no-till commercial agriculture that is practiced over much of the Southern Plateau region. Last, Guarda Mor watershed is cultivated in the same agricultural setting, while located on the edge of a transition from volcanic to sedimentary rocks. At these watersheds, rainfall-runoff events were monitored for discharge, sediment yield, water quality, and overall soil/land use and management. The sediment fingerprinting technique, and erosion and deposition inventories are tools that were also used. The results obtained over the years highlight the need for monitoring studies to quantify impacts and to plan and model scenarios for conservation planning. As they are used to improve runoff and erosion modelling at the watershed scale, which are then applied for simulating the most appropriate set of soil and water conservation practices. Practices that aim at maximizing agricultural yields, while improving water quality and quantity, focusing on attenuating maximum flows, and maximizing minimum flows.

Title: Operational Hydrology with NOAA’s National Water Model: Current Capabilities and Future Enhancements

Speaker: Brian Cosgrove, NWM Technical Director, NWS Office of Water Prediction

Description: Currently at version 3.0, the National Water Model (NWM) provides 24x7 guidance for streamflow and other hydrologic components used by NWS River Forecast Centers, the Federal Emergency Management Agency and other government entities, along with research and commercial sectors.  Based on the WRF-Hydro software architecture, it has been rapidly upgraded through six versions via a partnership between the NWS Office of Water Prediction (OWP), the National Center for Atmospheric Research (NCAR) and the National Centers for Environmental Prediction (NCEP). 

Building on NWM v2.2, NWM v3.0 became operational in summer 2023 and provides first-time total water level (TWL) forecasts for coastal areas of the CONUS, Puerto Rico, the U.S. Virgin Islands, and Hawaii. Complementing regional products, the system simulates the additive impacts of storm surge, tides and freshwater flow. For the first time, NWM v3.0 also features coverage for portions of Alaska. This presentation will provide an overview of current NWM operations and details on enhancements to TWL simulation capabilities arriving with NWM v3.1. It will also preview the transition to the Next Generation Water Resources Modeling Framework (NextGen) with NWM v4.0, and detail the Flood Inundation Mapping (FIM) capabilities supported by the NWM.NWS Office of Water Prediction (OWP).

Title: A Critical Evaluation of Statistical, Conceptual, and Machine Learning Tools for Streamflow and Flood Forecasting

Speaker: Ricardo Mantilla, Associate Professor, University of Manitoban

Description: Recently published literature has confirmed time and time again that machine learning (ML) algorithms (including LSTMs, GRUs, and Transformers) and classical lumped hydrological models (such as SAC-SMA and HBV) perform more reliably in hindcast and forecast flood prediction intercomparison experiments than more sophisticated high-resolution hydrological models. These provocative results have challenged decades of development of physics-based hydrological models for streamflow prediction, which seem to be more sensitive to the errors present in forcing precipitation data, and the spatial description of landscape attributes. Thus, the long-standing promise that a better and more detailed understanding and description of hydrological processes would yield better predictions of streamflow fluctuations (including floods, droughts, etc.) is yet to be fulfilled. I will show results from recent numerical experiments using high-resolution physics-based distributed hydrological models that shed some light into the applicability and limits of data-driven tools to predict the hydrological cycle under conditions of non-stationarity and noisy input information. The analysis is extended to investigate the class of statistical tools used for Regional Flood Frequency Analysis (RFFA) to determine the physical conditions required for classical techniques such as Index Flood Method. The results of this investigation highlight the need to establish causal physical links to the patterns in data reveled by data-driven analysis tools.

Title: Mapping Surface Water Dynamics with Cloud Computing and Open Source Software

Speaker: Qiusheng Wu, Associate Professor, University of Tennessee, Knoxville

Description: This webinar will provide an in-depth look at leveraging open-access satellite data, aerial imagery, cloud computing, and open-source so􀅌ware to map and analyze surface water dynamics.

Title: Using Water-power Models to Reconcile Climate Change, Hydropower, and Environmental Flows

Speaker: Gustavo Facincani Dourado, Water Resources Engineer, California Department of Water Resources

Description: Water allocation decisions for human and environmental needs depend on engineering structures, operational policies, and varying demands from multiple end-users. Assumptions about current and future scenarios help anticipate decisions to balance these objectives under different stressors, such as climate change. In this webinar, some study cases from California’s Central Sierra Nevada will be shown, to bring insights into balancing human and environmental needs, reservoir operations, hydropower generation, and water management.

Title: The Surprisingly Complex Challenge of Rain-Snow Partitioning, & Why It Matters

Speaker: Keith Jennings, Lead Hydrologist at Lynker

Description: While many look forward to winter snowfall, winter rains may bring devastating flooding. Despite the disparate outcomes of rain and snow, the hydrologic models we trust to make accurate streamflow forecasts often use flawed methods to determine what type of precipitation is falling at the land surface. This results in poor hydrologic predictions. At this point, one may wonder why such issues arise given the freezing point of water is an unequivocal 0°C. Unfortunately, this value happens to be a poor threshold for partitioning precipitation phase because precipitation is typically snow at 0°C and slightly higher air temperatures. Atmospheric temperature profiles, surface humidity, and pressure all affect whether it is raining and snowing, making phase partitioning a surprisingly complex challenge. In this webinar, we will detail the different types of precipitation, identify how hydrologic models differentiate rain versus snow, quantify the errors introduced by incorrectly simulating the precipitation type, and discuss several novel ways of monitoring precipitation phase.

Title: Sand Mines: Guilty Until Proven Innocent?

Speakers: Lee von Gynz-Guethle, Sr. Project Manager, WEST Consultants and Jerry Webb, Sr. Technical Advisor, WEST Consultants

Description: Lake Houston (the Lake) was formed in 1951 to impound the San Jacinto River north-east of downtown Houston, Texas to provide drinking water and recreational benefits. During the following decades, the areas around the Lake were heavily developed and the Lake’s capacity was reduced due to sedimentation. After repeated flood events, including Hurricane Harvey, there was widespread blame for sedimentation and flooding placed on sand mining operations. Local residents sued the sand mining operators and claimed they were the source of sedimentation and the cause of flooding. WEST Consultants (WEST) was hired as an expert witness in support of the sand mining operators. WEST conducted extensive literature reviews and hydraulic modeling to confirm whether sediment played a factor in property flooding during Hurricane Harvey and whether sand mining operations contributed significantly to lake sedimentation. This presentation will provide the audience an overview of these findings and an understanding of the role of sedimentation in the Lake.

Title: NOAA Atlas 15 - Generating Authoritative Climate-Informed Precipitation Frequency Estimates

Speaker: Janel Hanrahan, Research Scientist, RTI International

Description: The Office of Water Prediction (OWP) of the National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service (NWS) is responsible for the development, production, and publication of national precipitation frequency estimates. These estimates, which are used to design and manage infrastructure projects, must be regularly revisited to account for new data and improved methodologies. Under the Bipartisan Infrastructure Law, NOAA received funding to update precipitation frequency estimates nationwide, building upon an existing framework developed for NOAA Atlas 14, but now to account for climate nonstationarity. Once complete, high resolution gridded estimates will be published in two volumes of NOAA Atlas 15: Volume 1 will encompass present day and Volume 2 will provide estimates into the future. To facilitate understanding and to provide early insight into the development of NOAA Atlas 15, NOAA released pilot data over the state of Montana on a new web interface. Final estimates for U.S. states and territories are expected to be available in 2027. In this webinar, we will highlight features on the new Atlas 15 webpage, describe ongoing efforts to develop a national extreme time series data repository, and outline the frameworks used to generate both present-day and future estimates.

Title: Advancing Flood Risk Tools and Methods in the USACE

Speaker: Haden Smith, Lead Engineer, USACE

Description: The USACE Risk Management Center (RMC) supports Dam and Levee Safety Programs by developing tools, advancing methodologies, and overseeing complex projects. The RMC's flood hydrology team has pioneered tools to estimate flood frequency with uncertainty, aiding the assessment of over 700 dams and 10,000 miles of levees. These tools are also used for critical infrastructure risk analysis. Probabilistic Flood Hazard Analysis supports dam and levee risk assessments by generating flood hazard curves for peak stage, flow, and volume-duration probabilities. Core tools include RMC-RRFT (Rainfall-Runoff Frequency Tool), RMC-BestFit, and RMCRFA (Reservoir Frequency Analysis). RMC-TotalRisk integrates these analyses with event tree modeling. Web-based applications, including the Levee Screening Tool (LST 2.0) and Dam Safety Tool (DST), quantify risk using HEC-RAS 2D modeling, LifeSim, and national datasets. Future plans aim to integrate RMC’s flood hazard tools into these platforms. This presentation highlights RMC’s tools, methodologies, and future advancements.

Title: Global Challenges & Opportunities on Water Resources & Hydrology in the XXI Century

Speaker: Carlos A. Fernandez-Jauregui, Chief Visionary Officer, Water Assessment & Advisory Global Network

Description: In this webinar, Dr. Carlos will provide an insightful overview of global water availability and usage, highlighting the critical challenges we face in this century. He will explore strategies to overcome these challenges, uncover new opportunities, and emphasize that the current crisis is, at its core, a crisis of water governance at national, regional, and global levels.

Title: Remote Sensing Data and Discovery Tools to Support Water Resources Management

Speaker: Renato Frasson, Scientist, Jet Propulsion Laboratory, California Institute of Technology

Description: A wealth of information derived from spaceborne observations is freely available to any interested parties. Such data often offers global coverage and can be used to perform water availability assessments, identify areas under risk of flooding, observe river migration, and much more. Here, we describe the datasets produced by the Observational Products for Endusers from Remote sensing Analysis (OPERA) project. OPERA aims to remove barriers for the use of remote sensing data, making it accessible to practitioners, decision makers, and the community at large. In this talk, we will present the Dynamic Surface Water eXtent (DSWx), the Surface Disturbance (DIST), and the Displacement (DISP) products, alongside techniques for data discovery and download. We will finalize this webinar by showcasing examples of use cases developed by the OPERA team and stakeholders.

Title: The Journey to Improve US Federal Guidelines for Flood Frequency Analysis

Speaker: Jery R. Stedinger, D. C. Baum Professor of Engineering, Emeritus, Cornell University

Description: US Federal agencies agreed on uniform floodflow frequency procedures in 1976 with publication of the interagency U.S. Bulletin 17, updated to Bulletin 17B in 1982, and finally Bulletin 17C in 2018. In the run up to Bulletin 17C, an interagency workgroup (HFAWG) spent over a decade testing and developing new robust estimators. Important differences between Bulletin 17B and 17C are adoption of an Expected Moment Algorithm (EMA) that allows appropriate treatment of historical and paleoflood data, zero flows, censored crest-stage records, and “Potentially Influential Low Floods” (PILFs). Uncertainty analysis calculations were corrected. Recommended Bayesian regional Generalized-Least-Squares skew estimators indicate regional skews are more accurate that previously described; they are being developed for the whole U.S. The talk addresses technical developments, their motivation, and the perseverance of federal and academic hydrologists to work together to pursue needed technical developments and to have them eventually adopted for the U.S – from “mountains to the prairies to the oceans …” (Irving Berlin, 1938).

Title: Low and Behold: Extreme Weather Impacts to the Water Sector

Speaker: Sunny Wescott, Chief Meteorologist, Federal Emergency Response

Description: Extreme weather trends over the past 55 years have indicated a major swing in lower lows, and longer lasting highs which is wreaking havoc on weather systems at the surface. When systems and practices were established off the trends of the early 1900s or prior, the

considerations for worsening events were not anticipated to ever reach the events we are seeing at both an increasing frequency and greater intensity. Planning for stronger, persisting drying winds more often, heavier onsets of rain and/or snow, faster moving wildfires, subsidence risks, sea level rise triggering saltwater intrusion, extreme temperature fluctuations, and of course erratic changes to our tropical weather.

Title: Advancing Large-Scale Streamflow Predictions: From Reanalysis to Projections for the CONUS

Speaker: Ganesh Ghimire, R&D Staff Scientist, Oak Ridge National Laboratory

Description: Streamflow observations, essential for various water resource applications, are often unavailable at locations in need. Although different models have been proposed to enhance streamflow predictability at ungauged river reaches, the challenge involves more than just model fidelity. Uncertainties in meteorologic forcing datasets, particularly those related to precipitation, can play a more critical role in the accuracy of hydrologic predictions. It is even more challenging across regions characterized by diverse hydro-climatological and geographical conditions, such as in the conterminous US (CONUS). In this two-part talk, first I will highlight the calibrated VIC–RAPID hydrologic modeling framework we have implemented to develop multiple sets of 40-year (1980– 2019) streamflow reanalysis - Dayflow for 2.7 million river reaches across the CONUS. In the second part, I will discuss our efforts in understanding the impact of changing environmental conditions on water resources availability for multiple sectors, including hydropower. We leverage a multi-model ensemble approach that can account for uncertainty in projected hydroclimate, energy generation, and hydrologic response, streamflow in particular. I will then share the details on the consequent open-access ensemble streamflow projections dataset for the CONUS, associated insights, and its potential to address the data needs of a broader research and operations community.

Title: Can Site-Specific Flash-Flood Forecasts Be Achieved?

Speaker: Witold Krajewski, Professor, University of Iowa

Description: Recent tragic flash-floods in Texas and elsewhere exposed renewed interest in our abilities to forecast them ahead of time as well as the methods to communicate the potential warnings. The speaker will address these two aspects of the problem. He will summarize the results of a recent study of the benefits of the NOAA’s operational quantitative precipitation forecasting (QPF) product known as High Resolution Rapid Refresh (HRRR) on real-time stream flow forecasts using the NWS’s National Water Model. The insights obtained over the CONUS show strong scale dependence of the forecasting skill with the small (flash-flood) scales benefiting the least. This brings into the focus the overall architecture required of flood alert systems. The presenter will demonstrate the Iowa Flood Information System that has been working over the state of Iowa for the past 14 years and visited some 5 million times. This web-based system integrates observational and modeling data from federal agencies as well as the networks and forecasting systems deployed and operated by the Iowa Flood Center. The system which communicates in a jargon-free intuitive manner could serve as a template for other states and regions.

Title: Informational Design Applied to Environmental Time-Series Analysis and Visualization

Speaker: Richard Koehler, PhD, PH, CEO, Visual Data Analytics, LLC

Description: This presentation describes methods for analyzing and visualizing environmental time-series datasets using an informational design approach. The seminar outlines how these methods can generate products to identify data properties and trends previously hidden. Methods include a first-order differential technique and the use of a multilayer plotting system, similar to GIS but applied to temporal data. This facilitates prior and subsequent day conditional analyses as well as providing a visual estimation of autocorrelation across the dataset. Additional applications include model calibration techniques, sensitivity analysis, scenario planning, restoration monitoring, alternatives to traditional statistical indices, and broader options for data visualization. Examples from multiple US locations are presented and discussed.

Title: Urban Runoff and the Role of Stormwater Control Measures

Speakers: Aditi Bhaskar, Associate Professor University of Colorado Boulder; Benjamin Choat, Project Engineering, WEST Consultants, Inc

Description: This presentation will examine stormwater infrastructure effectiveness at a watershed-scale. For the past 20 years, streamflow, water quality, geomorphology, and benthic communities were monitored in 5 watersheds in suburban Washington D.C. The monitored watersheds include a forested control, an urban control with centralized stormwater management, and 3 suburban treatment watersheds featuring low-impact development and a high density of infiltration-focused stormwater facilities distributed across the watershed. We found effective imperviousness to better explain the ecological outcomes in the treatment watersheds compared to either directly connected imperviousness or total imperviousness.

Title: Storm Motion as a Driver of Flood Magnitude: New Tools for Flood Hazard Analysis

Speaker: Gabriel Perez, Assistant Professor, Oklahoma State University

Description: Flood magnitude is traditionally explained by watershed antecedent conditions and storm characteristics such as intensity, duration, and spatial extent. However, recent research highlights storm motion—the speed and direction of storm travel—as another key factor influencing flood response. This raises a critical question: if two storms are identical except for the path they take across a watershed, how different will the resulting floods be? And under what storm and watershed configurations do these differences matter most? I will present two modeling approaches that explicitly capture storm motion in rainfall-driven flooding. The first is the Directional Unit Hydrograph, a lumped model estimating hydrograph responses based on storm direction and speed. The second is a process-based flood frequency framework that combines distributed hydrologic modeling, stochastic storm transposition, and frequency analysis. Together, these approaches offer tools for engineering practice to improve flood hazard analysis under current and future climate conditions.