About

Samuel Muñoz is an Associate Professor in the Department of Marine and Environmental Sciences at Northeastern University. His research focuses on understanding hydrological extremes and their connections to the natural and built environment. He investigates the influence of climate variability, greenhouse warming, urbanization, and land use on flood risk, as well as how floods and climate-related disasters shape landscapes and their inhabitants. His work draws on historical and geological perspectives to evaluate the causes and consequences of storms and floods, often utilizing sedimentary records to reconstruct environmental changes over hundreds to thousands of years. Muñoz combines geological records with instrumental, historical, and archaeological datasets to inform computational approaches, including statistical and earth system models. His research has contributed to understanding climate change impacts on extreme weather events, flood prediction, and the broader implications of climate variability on infrastructure and ecosystems.

Research topics

• Biology
• Geology
• Geochemistry
• Astrobiology
• Environmental science
• Geography
• Physics
• Oceanography
• Physical geography
• Astronomy
• Archaeology

Selected publications

• Hydrologic Whiplash in the Mississippi River Basin: Mechanisms and Projections

  Geophysical Research Letters · 2026-05-12

  articleOpen accessSenior author

  Abstract Volatility and unpredictability of hydroclimate systems stresses planning and risk management. Notably, the rapid transition between periods of high and low streamflow, known as hydrologic whiplash, is gaining attention worldwide. Yet the specific mechanisms driving hydrologic whiplash events, and how they differ from singular events, remain poorly understood. We examine whiplash within the Mississippi River basin using observations and the Community Earth System Model version 2 Large Ensemble (CESM2‐LENS) to quantify historic occurrence on major tributaries and changes in frequency through the 21st century under a moderately high emissions scenario (SSP3‐7.0), and identify hydrologic mechanisms distinguishing these events from isolated events. We find that whiplash events increase in frequency most notably on western tributaries (Missouri, +115% and Arkansas, +137%), and that antecedent precipitation and snowmelt pulses or deficits initiate these whiplash events, while soil moisture anomalies can have opposite signs from those associated with singular events.

  PublisherDOI

• Twenty-First-Century Hydrological Trends in the Mississippi River Basin Intensify the East–West Moisture Gradient

  Journal of Climate · 2026-03-09

  articleSenior author

  Abstract The Mississippi River system drains 41% of the contiguous United States and is heavily engineered to mitigate hydrological extremes and facilitate commerce. However, future changes to water availability in the region are uncertain and may threaten the existing management systems. In this study, 19 models from Coupled Model Intercomparison Project phase 6 (CMIP6) are validated against historical observations and examined to understand monthly hydroclimate changes using the shared socioeconomic pathway 3-7.0 (SSP3-7.0) pathway. Models agree that precipitation will increase throughout the Mississippi River basin, but soil moisture will decrease in all seasons due to increasing evaporative demand. Precipitation minus evapotranspiration ( P − ET), runoff, and discharge simulated by river transport models are poorly constrained with differing trends between regions and models. Generally, models agree that runoff increases are more robust for the eastern subbasins, where precipitation anomalies are higher, and drying trends are more likely for the Missouri River subbasin. Models projecting increased runoff within the Mississippi River basin show stronger ENSO-related Pacific warming, enhanced North Atlantic subtropical high development, and increased moisture transport into the Ohio subbasin. In contrast, drying models exhibit weaker Pacific warming and circulation changes, with precipitation and runoff declines concentrated in the western tributaries. These results highlight the role of large-scale atmospheric and oceanic drivers in shaping divergent hydroclimate projections for the Mississippi River basin. Significance Statement Projections of future hydroclimate in the Mississippi River basin, the largest in North America, remain uncertain despite its critical role for agriculture and commerce. Using an ensemble of 19 models, this study provides the first comprehensive CMIP6 assessment of twenty-first-century hydrological trends across the basin. Our results reveal that precipitation will increase throughout the basin, particularly during winter and spring, and in the Ohio River subbasin. Total runoff projections are less certain, but climate models agree that discharge will increase in the Ohio and decrease in the Missouri subbasins. Water management strategies must consider this longitudinal pattern, as infrastructure built for twentieth-century conditions may face increasing risk from both high-flow and low-flow extremes in different portions of the basin.

  PublisherDOI

• Towards an improved understanding of the magnitude and drivers of carbon and nitrogen storage and accumulation in urban saltmarshes: a case study from New England (USA)

  Urban Ecosystems · 2026-03-17

  articleOpen access

  Urban saltmarshes, although often heavily modified yet critical for nature-based climate and water quality management strategies, remain insufficiently integrated into coastal sustainability policy and practice. This study quantified soil organic carbon (SOC) and nitrogen (SN) stocks and accumulation in Belle Isle Marsh, Boston, USA, using 26 soil cores collected to 1 m depth across upland transitional marsh, high marsh, low marsh, and unvegetated marsh habitats. Mean (± SD) SOC and SN stocks in the upper meter were 332 ± 144 Mg C ha− 1 and 17 ± 4 Mg N ha− 1, respectively, values comparable to global temperate saltmarsh estimates. High marshes consistently held the highest stocks, while unvegetated and upland transitional marsh habitats exhibited lower and more variable stocks. Stocks and accumulation were strongly influenced by dry bulk density and sediment-size distribution, reflecting how sediment composition affects carbon and nitrogen storage. Using ¹³⁷Cs radionuclide dating, sediment accretion rates ranged from 0.29 to 0.79 cm− 2 yr− 1, and corresponding to carbon and nitrogen accumulation rates from 80 to 183 g C m− 2 yr− 1 and 2 to 15 g N m− 2 yr− 1, respectively. These findings demonstrate that urban saltmarshes can sustain carbon and nitrogen stocks and burial rates comparable to global ranges, even under sustained anthropogenic pressure. However, the same forces that shape these systems also threaten their long-term storage capacity, underscoring the urgency of conserving and restoring urban wetlands and fully integrating them into regional and global carbon and nutrient management frameworks.

  PublisherOA PDFDOI

• Evaluation of hydroclimatic biases in the Community Earth System Model (CESM1) within the Mississippi River basin

  Hydrology and earth system sciences · 2025-09-25 · 1 citations

  articleOpen accessSenior authorCorresponding

  Abstract. The Mississippi River is a critical waterway in the United States, and hydrologic variability along its course represents a perennial consideration for trade, agriculture, industry, ecosystems, the economy, and communities. Simulations of past, historic, and projected river discharge have been widely used to assess the dynamics and causes of changes in the hydrology of the Mississippi River basin over long time scales and to put changes of climate in context. The Community Earth System Model version 1 (CESM1) offers such simulations to complement observational records of river discharge by providing fully coupled output from a state-of-the-art earth system model that includes a river transport model. Here, we compare observations and reanalysis datasets of key hydrologic variables to CESM1 output within the Mississippi River basin to evaluate model performance and bias. We show that the seasonality of simulated river discharge in CESM1 is shifted 3 months late relative to observations. This offset is attributed to seasonal biases in precipitation and runoff in the region. We also evaluate performance of several Coupled Model Intercomparison Phase 6 (CMIP6) models over the Mississippi River basin, and show that runoff in other models – notably the Community Earth System Model version 2 (CESM2) – more closely simulates the seasonal trends in the reanalysis data. Our results have implications for model selection when assessing hydroclimate variability on the Mississippi River basin, and show that the seasonal timing of runoff can vary widely between models. Our findings point to (1) a need for continued developments in the representation of land surface hydrology in earth system models for improvements in our ability to assess the causes and consequences of environmental change on terrestrial water resources and major river systems globally, and (2) a need for caution and understanding of biases when applying these tools to practical risk assessment.

  PublisherOA PDFDOI

• Connecting Large‐Scale Atmospheric and Land Surface Patterns to New England Riverine Peak Flow Events

  Geophysical Research Letters · 2025-09-30

  articleOpen accessSenior author

  Abstract Riverine flooding in the New England region of the United States of America is devastating, arises from multiple processes during any season, and lacks ties to common climate indices. Here the connection between large‐scale atmospheric patterns and surface conditions prior to and during the occurrence of riverine peak flow events in the heavily‐populated, flood‐vulnerable region of New England is explored. Understanding the mechanisms governing peak‐flows improves the near‐ and long‐term forecasts of hydroclimatic extremes as well as provides supplemental process‐level knowledge for regional water resource planning and emergency response. Through the application of self‐organizing maps, several distinct meteorological and hydrological patterns associated with river discharge events in New England are identified. Using case‐studies of major floods in July and December of 2023, we demonstrate that this methodology provides a mechanistic foundation for understanding the drivers of New England floods and how they might change in a future climate.

  PublisherDOI

• Climatic versus Anthropogenic Influences on Sediment Delivery to the Gulf of Mexico Marginal Sea since 5000 y BP

  2025-03-14

  preprintOpen accessCorresponding

  We present a compilation of provenance data derived from the lower reaches of the Mississippi river showing how the source of sediment supplied to the lower reaches has changed through time in the recent geologic past. We integrate data from a late Holocene point bar, its associated oxbow lake (False River) and the channel plug that infilled since ~500 y BP, as well as another oxbow located upstream at Lake St John. Another finer grained sediment record was derived from coring close to the Mississippi south of New Orleans. The sediments were analysed for an array of major elements, Sr and Nd isotopes, as well as detrital zircon U-Pb geochronology. Grain size is a critical factor in controlling the provenance because suspended sediment is transported rapidly through the river compared to coarse-grained material which travels more slowly as bedload. The radiogenic isotope signature of the fine-grained sediment shows a long-term shift since 4.5 ka towards more radiogenic signatures indicative of more erosion from ancient continental crust, likely the Appalachians and Mid Continent rather than the Rocky Mountain foreland, although this remains the dominant source of material supplied to the Gulf of Mexico. While some of this shift may be anthropogenic, the trend suggests long-term drying of the continental interior and reduced erosion of the foreland. Nonetheless, sand-silt sized zircon U-Pb ages indicate that between 1600 and ~1920 CE flood sediments were dominated by supply from the Missouri River, which is largely sourced from the Rocky Mountain foreland. From 500 BCE until 1600 CE supply was more skewed to the Upper Mississippi and Red River, and with some input from the Arkansas River, also derived from the west. Coarse grained sediments deposited in the lower reaches during the last 10 years show a high degree of variability which we interpret to reflect reduced sediment buffering driven by the inability of the lower reaches to meander and recycle flood sediments in the way expected prior to the installation of levees. The modern tributaries all carry sediment that is much more altered than was true in the recent geological past and reflects heightened soil erosion driven by agriculture. The modern Mississippi is a poor analogue for the natural state of the river when compared to ancient geological deposits.

  PublisherDOI

• Climate Variability in the Gulf of California Over the Last 1,300 years

  Paleoceanography and Paleoclimatology · 2025-02-01 · 2 citations

  article

  Abstract The North American Monsoon influences the ecosystems and hydroclimate of the southwestern United States and northwestern Mexico. This is a geographically complex region, including the narrow Gulf of California adjacent to the Sierra Madre Occidental. Alongside this complexity, unreliable gridded data products, a lack of long instrumental observations, and limited high‐resolution paleoclimate records from the core monsoon region prevent a complete understanding of the variability and drivers of this system on time scales from decades to millennia. Here we generate new proxy records of warm‐season sea‐surface temperature (SST, based on alkenone ) and terrestrial hydroclimate (based on plant wax hydrogen isotopes) from Gulf of California (GoC) sediment cores spanning 744 to 1980 CE. Although the GoC is an important source of monsoon moisture, we find no one‐to‐one correlation between SST and our hydroclimate reconstruction over the full time period. Spectral analyses revealed a prominent multicentennial oscillation in the SST reconstruction, as well as multidecadal modes in both records. There is a small cooling trend over the full SST reconstruction, but no clearly delineated Medieval Climate Anomaly or Little Ice Age. Colder periods in our SST reconstruction appear to be associated with periods of increased volcanism, but there is no definitive solar signal. Multidecadal climate variability in this region is likely linked to broader patterns of unforced variability in the Pacific Ocean‐atmosphere system, but any coupling between monsoon strength and Gulf of California SST over the Common Era appears to be complex.

  PublisherDOI

• Drying of the Panama Canal in a Warming Climate

  Geophysical Research Letters · 2025-09-17

  articleOpen access1st authorCorresponding

  Abstract The Panama Canal is an artery of global trade, connecting the Atlantic and Pacific Oceans and relying on water from Gatún Lake to operate its lock system. During droughts, falling lake levels force the Autoridad del Canal de Panamá to restrict ship transits, disrupting international supply chains. Recent droughts have raised concerns about how climate change could affect canal operations. Here we present new simulations of Gatún Lake levels using statistically downscaled, bias‐corrected model projections. We find that minimum annual lake levels decline substantially through the 21st century under higher emissions pathways (SSP3‐7.0 and SSP5‐8.5), driven primarily by reduced wet season rainfall. Though the magnitude of future drying in Central America remains uncertain, these projections—holding operational practices constant—highlight the growing risk of disruptions without adaptation or emissions mitigation. The Panama Canal illustrates both the need for infrastructure adaptation and emissions reductions to limit economic risk.

  PublisherOA PDFDOI

• Multiple paleofire proxy metrics from tropical lake sediment and soil in the Greater Serengeti Ecosystem

  The Holocene · 2025-06-26

  articleOpen access

  Black carbon is a paleofire proxy that has been measured from glacial ice, snow, soils and lake sediments, though relatively few comparisons have been made with other fire indicators in sedimentary geoarchives. Microscopic charcoal, quantified from palynological microscope slides and macroscopic charcoal, quantified from wet-sieved deposits, are the most commonly applied methods for paleofire interpretation of Quaternary sediments. This research explores the down-profile patterns across three paleofire proxies (refractory black carbon, microscopic and macroscopic charcoal) and potential paleofire interpretations from a sediment core dating to the last centuries from Speke Gulf, Lake Victoria, and a young soil profile from a kopje located in the surrounding watershed in Serengeti National Park, Tanzania. The results of three paleofire metrics show similar trends within each site, with a positive trend across all metrics and increasing variability with increased measurement values (heteroscedastic). Notably, refractory black carbon (rBC) concentrations are two orders of magnitude higher in lake sediment samples compared to soil samples. rBC is positively correlated with both microscopic and macroscopic charcoal values and the overall profile patterns down the sediment core are similar, with the exception of the rBC increases from 2.5 to 0 cm depth that may result from increased fossil fuel combustion. The Speke Gulf rBC measurements are in an intermediate range between those published from glacial ice and other lake sediments. New rBC records from different ecosystems and temporal scales will provide paleofire insights and potential to interpret source areas and depositional patterns. The exploration of soil archives offers the potential to exploit semi-arid ecosystems and archaeological sites that have no nearby traditional paleoenvironmental study site targets.

  PublisherDOI

• Contrasting Size Dependence of Photochemical Lifetimes of Polypropylene and Expanded Polystyrene Microplastics in Surface Waters

  Environmental Science & Technology · 2025-12-02 · 1 citations

  articleOpen access

  Microplastics are found floating on natural waters. Sunlight-driven photochemistry can dissolve buoyant microplastics, producing dissolved organic carbon (DOC). We hypothesized that plastic dissolution would increase linearly with increasing surface area (SA)-to-volume (V) ratio as plastics decrease in size. To test this, samples of expanded polystyrene (EPS) and polypropylene (PP) spanning a range of sizes were irradiated while floating on water in a solar simulator. A linear relationship between SA:V and DOC accumulation rate was significant for EPS (p < 0.0001) and PP (p = 0.0086), suggesting SA-controlled reactions. However, a power relationship with an exponent of approximately 0.5 between PP dissolution and SA:V provided a significantly better fit, suggesting that non-SA-controlled processes may limit PP photodissolution. Using these relationships, it was estimated that macroplastics ∼10 cm should take ∼250 to ∼8000 years to photochemically dissolve. However, estimated lifetimes are shorter for smaller plastics, with 1 mm EPS beads and 100 nm PP nanoplastics estimated to have lifetimes of 5.3 years and 3 to 196 days, respectively, with the range in lifetimes for PP dependent upon whether linear or power fits are applied.

  PublisherDOI

Recent grants

• Collaborative Research: Reevaluating precipitation extremes and flood hazard in the wake of Hurricane Harvey

  NSF · $200k · 2018–2022

• Collaborative Research: Evaluating the Past and Future of Mississippi River Hydroclimatology to Constrain Risk via Integrated Climate Modeling, Observations, and Reconstructions

  NSF · $284k · 2022–2026

• Collaborative Research: P2C2: Extreme floods on the lower Mississippi River in the context of late Holocene climatic variability

  NSF · $342k · 2018–2023

Frequent coauthors

• Charlotte Wiman

  Northeastern University

  23 shared

• Sylvia Dee

  Rice University

  14 shared

• Joeri B. Reinders

  Leiden University

  13 shared

• Liviu Giosan

  12 shared

• Sissel Schroeder

  University of Wisconsin–Madison

  11 shared

• Zhixiong Shen

  11 shared

• Nicholas P. McKay

  Northern Arizona University

  10 shared

• Lora Stevens

  9 shared

Education

• PhD, Geography

  University of Wisconsin Madison

  2015

• M.Sc., Geography

  University of Ottawa

  2010

• B.Sc., Geography

  Carleton University

  2008

Awards & honors

• NSF CAREER Award