Victor R. Baker’s research while affiliated with The University of Arizona and other places

Ephemeral alluvial streams pose globally significant flood hazards to human habitation in drylands, but sparse data for these regions limit understanding of the character and impacts of extreme flooding. In this study, we document decadal changes in dryland ephemeral channel patterns at two sites in the lower Colorado River Basin (southwestern United States) that were ravaged by extraordinary flash floods in the 1970s: Bronco Creek, Arizona (1971), and Eldorado Canyon, Nevada (1974). We refer to these two floods as ‘fluviomorphic erasure events’, because they produced blank slates for the channels that were gradually moulded by more frequent but much smaller flood events. We studied georectified aerial photos that span ~60 years at each site to show that both study sites recovered to their pre‐flood condition after ~25 years. We employ channel network metrics: stream‐link area (SLA), geometric braiding index and junction‐node density. Each metric decreased during the short‐duration extreme flood erasure events. Subsequently, a fluviomorphic trajectory at a decadal tempo returned the channels to pre‐flood values. The SLA decreased at rates of 3.6%–4.1% per year in the decade following the floods. The extreme flood events decreased the pre‐flood geometric braiding index at the two sites by 56%–68%, and it took 15–24 years for this index to recover to pre‐flood values. In contrast, it took 30–35 years for the channels to recover to a uniform pre‐flood channel form, as indicated by the spatial distribution of bars and junction nodes. Our results document baseline examples of ephemeral stream channel evolution trajectories, as future climatic change will likely accelerate increases in the magnitudes and frequencies of extreme floods and geomorphic erasure events.

Abstract: Hydrologic modeling is an essential tool for analyzing the environmental effects of wildfires. Simulations of watershed behavior are uniquely suited to emergency assessments in which data are limited and time is scarce, such as those performed under the Burned Area Emergency Response (BAER) Program used by Federal Land Management Agencies in the United States. In these situations—when the values at risk (VARS) include lives and property—it is critical to remember: “All models are wrong, but some are useful” (Box and Draper, 1987). However, all too often, neither reports nor results rigorously reflect this imperative. With the wildfire crisis worsening each year, improving the state of the practice can be a strategic force multiplier for agencies, NGOs, and researchers alike. Herein, the twin questions of how wrong and how useful are used as the foundation for an overview of meaningful modeling within the context of postfire hydrologic assessments. Therefore, this paper focuses on how to: (1) think about watershed modeling, (2) select a modeling strategy, and (3) present the simulations in a meaningful way. The beginning and the end—the bread of a modeling sandwich. Nearly a third of the content is about science communication. While the focus is on burnt watersheds, BAER, and the US, the basic principles of modeling, grappling with uncertainty, and science communication are universal—and often not taught in many academic programs. [This provisional version has not undergone use testing or formal review by theUS Forest Service and will continue to evolve until the agency officially releases it. However, it was included as chapter 9 of Wheelock S.J. (2024) Marscapes to Terrestrial Moonscapes: A Variety of Water Problems."

Addressing post-fire impacts largely depends on burn “severity.” A singular severity classification that encompasses the holistic effects of fire on all ecosystem processes does not currently exist. Lumping vegetation burn severity and soil burn severity into one metric, or using them interchangeably, can induce large inaccuracies and uncertainties in the intended ecosystem response to forcing. Often, burn “severity” reflects fire impacts on vegetation, which can be measured through remote sensing. Vegetation burn severity is likely more apropos for ecological research, whereas soil burn severity is more relevant for hydrological analyses. This paper reviews different remotely sensed vegetation severity products currently (mis)used for hydrological modeling, provides examples of when vegetation burn severity may (not) match soil burn severity, and summarizes the potential synergistic future of remote sensing with in situ severity metrics. While the focus in this paper is on the western United States, the lessons and principles apply universally.

Ancient Martian orogenesis remains controversial, ranging from mantle plumes to continental-scale gravity sliding to plate tectonism. Here, we consider Claritas Rise, an ancient, complex, Martian orogeny, as a case study in mountain building resulting from mobile lithospheric activity, using a geologic synthesis of comparative planetology. Claritas's juxtaposed serpentine and carbonate rocks, along a structurally controlled margin, compares to Earth's serpentine mélanges (e.g., Altai) that result from continental collisional processes. A less dense, older, deformed felsic/feldspathic crust may cause Claritas's gravity lows, as occurs in Earth's convergent plate boundary settings (e.g., Himalayas, Japan, Andes). This geochemically matches its regionally elevated incompatibles, potassium and thorium, relative to younger embaying lava flows. Claritas’ tectonic structures geometrically resemble the transtensional-extensional features of the Baikal Rift System located in southeastern Russia. Steeply dipping beds along a northeast-oriented ridge of Claritas also contain blocks resembling Earth's olistostromes. A mega-geomorphological pattern of landforms, including Claritas at its center, approximates that of the Western United States (i.e., where denser mafic Farallon Plate subducted beneath the buoyant, mafic/felsic North American Plate). An ancient mobile lithosphere offers a unifying explanation for these Earth counterparts on Mars while also addressing other features of interest, including crustal thickness differences across the topographic dichotomy and andesite-granite detections.

A great many of Earth’s major rivers experienced the influence of megafloods associated with the margins of large late Pleistocene ice sheets. Connected systems and large‐scale pathways of glacial flood spillways were associated with all the great continental ice sheets, and those of the Eurasian ice sheets may have temporarily constituted the largest terrestrial river system. Up until the early nineteenth century, considerable progress was being made in understanding the role of cataclysmic flooding for the geological evolution of river valleys. Continental ice sheets that form during epochs of glaciation exert immense influences on water drainage across the land. The whole system of Asian spillways and megalakes temporarily constituted Earth’s longest river, over 8000 km in length. Thus, the late Quaternary glacial phase of the northern hemisphere was marked by widespread magafloods and megarivers.

Professor Kenneth J. Gregory was a major contributor to fluvial palaeohydrological research. Beginning in the early 1980s, under his influence, rapid international growth of the discipline was accompanied by major advances in research methods and techniques. Current research emphases include applications of quantitative modeling and meta‐analysis; the correlation of fluvial events to other records, notably palaeolacustine records; and methods for application to diverse issues of river engineering and management. The international expansion and detailed analyses of fluvial palaeohydrolgy are exemplified by recent studies done in Fennoscandia, the Mediterranean region, India, Israel, Australia, Pacific humid island arcs, and South America. Future developments will involve expanded work with other academic disciplines, such as archaeology, as well as applications to practical problems arising from future climatic change and related environmental hazards, particularly extremes. Remote sensing and high‐resolution topography data and tools (e.g., LiDAR) will facilitate new discoveries of ancient exceptional flooding phenomena (megaflooding and superfloods) on Earth and on the palaeofluvial forms of Earth‐like planets. New opportunities will also arise from the increased use of machine learning and artificial intelligence for analyses of “big data.”