The Bengal Basin is a sedimentary basin in the northeast region of the Indian subcontinent. It lies between the Indian Shield and the Indo-Burma Ranges, where the India plate is obliquely subducting under the Burma microplate. Multiple interpretations of the nature of the crust here have been proposed. Using a compilation of data from 40 regional broadband stations, we determine the crustal structure by waveform modeling receiver functions and autocorrelograms. We obtain useful velocity models for 30 stations with 2-3 sedimentary units overlying the crystalline crust. The sedimentary section is up to 16.4 km thick with depths increasing from northwest to southeast. The first two sedimentary units have mean thicknesses of similar to 3.2 and similar to 6.5 km and Vp values of similar to 2.8 and similar to 4.9 km/s, respectively. Below these units, large negative Ps conversions are present, which we interpret as two low-velocity zones in the deepest portion of the Bengal Basin, with average Vp and Vp/Vs values of 4.2 km/s and 1.90. The low seismic velocities could be a result of fluids trapped in the deepest sedimentary unit. Below the sedimentary section the thickness of the crystalline crust varies from 12.9 to 34 km, thinning from northwest to southeast in the opposite general trend of basin depth, with an average Vp of 6.7 km/s. The crystalline crust is thinner and faster than typical continental crust and thicker and slower than typical oceanic crust. We suggest the region has extended continental crust that was altered during the Cretaceous rifting that created the Bengal Basin.

The Calabrian forearc separated from Sardinia ~10 Ma and migrated to the ESE, creating an oceanic basin (the Tyrrhenian Sea) in its wake and colliding obliquely with Apulia to build the southern Apennines. The time transgressive, spatially asymmetric nature of oblique collisions leads to along-strike migration of active geologic processes. Lack of evidence for large thrust earthquakes and conflicting geodetic evidence of Calabria-Apulia convergence contribute to the predominant belief that this process has completely ceased. Indicators of thrusting and steady state uplift from the Pleistocene into the Holocene are evident from field observations in the southernmost internal Apennines (Pollino Massif) and marine terrace ages on the external Apennines along the Gulf of Taranto (Metaponto). Terrace uplift rates increase dramatically southward, reaching a maximum of 1 mm/yr at the boundary between Pollino and Metaponto. Uplift rates may continue to increase southward in tandem with the structural and topographic relief across the Apenninic core, but correlation of marine terraces southward to the Sibari Plain becomes problematic because of steep slopes, erosion, and mass wasting. Any chronology of marine terrace ages used for determination of uplift rates and variability will need confirmation by abundant independent age constraints. Constraining uplift rates may be further complicated by a “corrugated detachment” (CD), a regionally exposed kinematic contact along the topographic axis of the southern Apennines between underlying carbonate and overlying flysch. This surface is believed to represent an active gravity-driven detachment with ESE tectonic transport down–slope of the collision wedge. Ductile deformation features within the exposed carbonate suggest burial depths of 1-2 km, and thus a currently active CD might be buried beneath the marine terraces ESE of the Pollino Massif. An active detachment above a rising footwall could lead to underestimates of tectonic uplift rates, and consequently misinterpretations of seismic risk. Recent advances in InSAR technology can resolve elastic deformation preceding seismogenic fault ruptures, as well as aseismic motion on faults, folds, and slumps through high-resolution velocity fields derived from accumulated datasets over the past decade. A coordinated effort coupling field-based observation, a detailed geochronology of marine and fluvial deposition, and high resolution InSAR analyses is needed to determine whether the current deformation is consistent with a continued Calabria-Apulia collision and to better constrain the seismic hazard in south Italy.

In Bangladesh's delta, rural communities have long held lives inseparable from seasonal flooding, adapting their homes and livelihoods to the annual monsoon. However, land subsidence, changing seasons, severe storms, increased salinity, and rising sea levels are threatening local livelihoods. The objective of this paper is to understand rural residents' perceptions of climate impacts and adaptation measures, focusing on their mobility choices. Through 15 qualitative, semi-structured interviews with 22 representatives from two embanked polder localities in southwest Bangladesh, we explored the following questions: (i) How do local residents perceive recent climate and environmental changes? (ii) How are local residents coping with these changes and what external assistance do they require to maintain their livelihoods; and (iii) How do local residents perceive migration or partial migration as a potential adaptation strategy? While these communities report an increased frequency of extreme climate events and severe flooding, our findings also reveal a lack of external assistance for adaptation solutions. Moreover, most families are either unwilling or unable to completely migrate out of affected areas. Therefore, increased support—the provision of fresh drinking water, money to recoup lost income and assistance rebuilding or reinforcing homes—is essential for building adaptive capacity and increasing local resilience in the face of climate shocks.

Landlab is an open-source Python package that streamlines the creation, combination, and reuse of 2D numerical models and is a key element of the Community Surface Dynamics Modeling System (CSDMS) Workbench. The Landlab Toolkit provides building blocks for model development such as grid data structures, input/output functions, and a library of several dozen components that each model a separate physical process. Additionally, it provides a framework for assembling integrated models from component parts. We've found that Landlab significantly accelerates model development, encourages user-developers to adopt standard practices and contribute new components to the library. It serves as a platform that nurtures a community of model developers, assisting them in creating coupled models to investigate non-linear interactions between geologic processes. Using the Landlab toolkit, we developed a new model, Sequence, which is a modular 2D (i.e., profile) sequence stratigraphic model that incorporates key geophysical processes influencing accommodation space in both terrestrial and marine environments. These factors include tectonics and faulting, eustatic sea level changes, flexural isostatic compensation of sediment and water, sediment compaction, and hypopycnal sediment plumes. Each process is encapsulated as an individual, standalone Landlab component, providing flexibility in the construction of new models. Sequence serves not only as a distinct model, but also as a scaffold for the development of new models. Sequence simulates the evolution of stratigraphy on a continental margin over time scales ranging from thousands to millions of years. Sediment transport and deposition primarily occur during infrequent, high-energy events like storms and floods. For these extended time frames, Sequence employs a scale-integral approach. This method utilizes differential equations to summarize the cumulative effect of sediment transport and deposition across different depositional environments over longer periods (e.g., on the order of a hundred years). The model features a moving-boundary formulation to track shoreline changes and partitions the domain into distinct areas: coastal plain, continental shelf, and upper and lower slope/rise. Submarine sediment transport and deposition are modeled through nonlinear diffusion, with a diffusion coefficient that varies inversely with water depth. The model tracks evolving stratigraphic layers and sediment lithology that is a mixtuer of two grain sizes (sand and mud) each with separate transport functions.

The Indo-Burma subduction zone (IBSZ) is an entirely subaerial plate boundary, where the Indian plate obliquely converges with the Burma microplate. Because the incoming plate includes the 16-20 km thick sediment of the Ganges-Brahmaputra Delta, the accretionary prism is over 250 km wide with numerous active splay thrust faults and strike slip faults. Accurately assessing the long- and short-term dynamics of this complex region is critical for determining its earthquake hazard. However, due in part to insufficient geodetic observations in the region to constrain the 3D shape of the megathrust and upper plate deformation, the kinematics of this plate boundary zone remain controversial. Ongoing debates focus on how strain is partitioned between the megathrust and strike-slip and oblique faults, whether the subduction zone is locked, and whether the multiple anticlines of the accretionary prism foldbelt are locked or actively deforming aseismically. In this study, we present the first large-scale Interferometric Synthetic Aperture Radar (InSAR) velocity field over the IBSZ. Considering the operational nature and radar characteristics of different satellites, we processed datasets of multiple satellites spanning from late 2014 to 2023, including Sentinel-1, ALOS-2, and the newly launched L-Band differential InSAR satellite of China, LuTan-1. This approach allows us to more accurately constrain deformation across such a heavily vegetated and topographically-varied region. We incorporated updated horizontal and vertical GNSS velocities from 60 sites obtained from 2003 to 2023 to derive a three-dimensional decomposed velocity field, and then we investigated faults activities by estimating interseismic strain rates across the IBSZ. Our preliminary results reveal how strain is distributed in the region, shedding light on seismic hazard across this densely populated area.

We hypothesize that brackish groundwater within unconfined aquifers located in active river deltas may have resulted from rapid shoreline progradation during the Holocene. To explore this hypothesis, we develop a coupled model of variable‐density groundwater flow and solute transport within a prograding sedimentary delta. In this model, the continuously evolving sedimentary delta domain is developed by laterally advancing a geometrically defined clinoform into an ocean with a changing sea level. To numerically solve the model, we used the control volume finite element method, where the numerical grid evolves in response to the changing delta geometry, while enforcing local mass balance around each grid node point. Results show that, if the lateral groundwater velocity is slower than the shoreline propagation rate, transient trapping of saline water occurs onshore. This process can be characterized by the product of two dimensionless number groups (a) the ratio of the shoreline velocity to the lateral average linear groundwater velocity and (b) a Peclet number quantifying the level of mixing between recharge freshwater and existing saline water. The presence of confining units enhances the sequestration of onshore seawater behind an advancing shoreline. Our results complement prior numerical modeling studies that demonstrate that salinity within onshore aquifers is enhanced by vertical diffusion of solutes out of marine confining units.

The shallow portion of a megathrust represents the zone of first contact between two colliding plates, and its rheological properties control the seismic and tsunami hazards generated by the fault. The high cost of underwater geodetic data collection results in sparse observations, leading to limited constraints on the interseismic behavior of megathrusts. The Rakhine-Bangladesh megathrust offers a unique opportunity to probe the behavior of the shallow megathrust as it is the only ocean-continent subduction zone where the near-trench region is fully accessible on land. Here, we use observations from ALOS-2 wide-swath imagery spanning 2015 to 2022 to conduct an InSAR timeseries analysis of the overriding plate within Bangladesh and the Indo-Myanmar Ranges. We identify a narrow pattern of alternating uplift and subsidence associated with mapped anticlines but show that it cannot be explained by slip on the megathrust or other fault structures. Instead, we argue that the deformation is likely caused by active aseismic folding within the wedge above a shallow decollement. We show that estimates of the decollement depth derived from a viscous folding model and the observed anticline spacing are in agreement with previous seismic observations of the decollement depth across the fold belt. We suggest that the role of ductile deformation in the overriding plate in subduction zones may be more important than previously recognized.

We utilized shear wave splitting analysis of teleseismic SKS, SKKS, and PKS phases to infer upper mantle deformational fabrics across a substantial area of Southeast Asia, where splitting measurements were previously limited. We used newly available permanent and temporary broadband seismic networks deployed across the Indo-Burma subduction zone and the eastern Indochina peninsula. The resulting 492 well-constrained splitting and 654 null measurements from 185 stations reveal clear large-scale patterns in the mantle deformational fabrics in response to the highly oblique active subduction and a large transform plate boundary. We identified two distinct domains of mantle deformation fabrics in the western Burma microplate and the eastern Indochina peninsula. In the former, trench parallel N-S fast polarization directions with an average lag time (delta t) of 1.9 s are observed beneath the Indo-Burman Ranges. We suggest the observed splitting is partly due to anisotropy in the sub-slab region and relates to shear induced by the north moving Indian plate. The lithospheric fabric within the Indo-Burman Ranges and underlying subducting slab fabric contribute to produce the observed average delta t of 1.9 s. The delta t value decreases to an average of 1.0 s towards the back-arc until we reach the dextral Sagaing fault. In the second domain, starting approximately 100 km east of the Sagaing fault, we observe a consistent E-W fast direction with an average delta t of 1.10 s in the eastern Shan-Thai and Indochina blocks. We interpret the E-W fabric as due to the deformation associated with the westward spreading of the Hainan mantle plume, possibly driven by overriding plate motion. Low velocities in the shallow mantle and late Cenozoic intraplate volcanism in this region support the plume-driven asthenospheric flow model in the Indochina peninsula. The sudden transition of the fast polarization direction from N-S to E-W along the eastern edge of the Burma microplate indicates the Sagaing fault acts as a mantle flow boundary between the subduction dominated trench parallel flow to the west and plume induced asthenospheric flow to the east. We also observed no net splitting beneath the Bengal basin which is most likely due to the presence of frozen vertical fabric resulting from the Kerguelen plume activity during Early Cretaceous.

The Ganges-Brahmaputra Delta (GBD) in Bangladesh exists at a nexus of stability and vulnerability, as the rivers annually carry 800–1000 MT of sediment from the Himalayan Mountains, yet coastal poldering and sediment extraction within the rivers remove elevation capital from the low-lying delta plain. Recent research in the GBD has begun to unravel how the world’s largest fluvio-deltaic mangrove forest—the Sundarbans—is keeping pace with sea level rise (SLR); however, this is contingent on adequate sediment supply delivered to the platform during semi-diurnal tides and the seasonal monsoon. Little is known about the elevation dynamics within human-modified polders by comparison, other than an elevation deficit of 1–1.5 m exists. In this study, seasonal data from Rod Surface Elevation Tables (RSETs) installed within a polder in the southwest region (Polder 32) are compared to the Sundarbans. Over 8 years, results show that surface elevation is gaining within the Sundarbans at a more significant rate ( 58.4

The Enriquillo-Plantain Garden fault (EPGF), the southern branch of the northern Caribbean left-lateral transpressional plate boundary, has ruptured in two devastating earthquakes along the Haiti southern peninsula: the M-w 7.0, 2010 Haiti and the M-w 7.2, 2021 Nippes earthquakes. In Jamaica, the 1692 Port Royal and 1907 Great Kingston earthquakes caused widespread damage and loss of life. No large earthquakes are known from the 200-km-long Jamaica Passage segment of this plate boundary. To address these hazards, a National Science Foundation Rapid Response survey was conducted to map the EPGF in the Jamaica Passage south of Kingston, Jamaica, and east of the island of Jamaica. From the R/V Pelican we collected >50 high-resolution seismic profiles and 47 gravity cores. Event deposits (EDs) were identified from lithology, physical properties, and geochemistry and were dated in 13 cores. A robust C-14 chronology was obtained for the Holocene. A Bayesian age model using OxCal 4.4 calibration was applied. Out of 58 EDs that were recognized, 50 have ages that overlap within their 95% confidence ranges. This allowed for their grouping in multiple basins located as much as 150 km apart. The significant age overlap suggests that EDs along the Enriquillo-Plantain Garden plate boundary resulted from large and potentially dangerous earthquakes. Most of these earthquakes may derive from the EPGF but also from thrust faulting at this strain-partitioned transpressional boundary. The recent increase in Coulomb stress on the EPGF from the M-w 7.2 Nippes earthquake in southwestern Haiti and the discoveries reported here enhance the significance for hazard in the Jamaica Passage.

Abstract Earthquakes present severe hazards for people and economies and can be primary drivers of landscape change yet their impact to river-channel networks remains poorly known. Here we show evidence for an abrupt earthquake-triggered avulsion of the Ganges River at ~2.5 ka leading to relocation of the mainstem channel belt in the Bengal delta. This is recorded in freshly discovered sedimentary archives of an immense relict channel and a paleo-earthquake of sufficient magnitude to cause major liquefaction and generate large, decimeter-scale sand dikes >180 km from the nearest seismogenic source region. Precise luminescence ages of channel sand, channel fill, and breached and partially liquefied floodplain deposits support coeval timing of the avulsion and earthquake. Evidence for reorganization of the river-channel network in the world’s largest delta broadens the risk posed by seismic events in the region and their recognition as geomorphic agents in this and other tectonically active lowlands. The recurrence of comparable earthquake-triggered ground liquefaction and a channel avulsion would be catastrophic for any of the heavily populated, large river basins and deltas along the Himalayan arc (e.g., Indus, Ganges, Brahmaputra, Ayeyarwady). The compounding effects of climate change and human impacts heighten and extend the vulnerability of many lowlands worldwide to such cascading hazards.

Coastal regions are vulnerable to rising seas, increasing storm magnitude, and decimation of ecologically-fragile areas. Deltas are particularly sensitive to the balance between sea-level rise, land subsidence and sedimentation that determine relative elevation. Bangladesh has been highlighted as being at risk from sea-level rise. Integrating measurements from different methods can approach a more complete understanding of factors controlling areally and temporally varying subsidence rates. To augment our compilation of rates from stratigraphic wells, historic buildings, vertical strainmeters, RSET-MH, and continuous Global Navigation Satellite System, we resurveyed 48 geodetic monuments in coastal Bangladesh ∼18 years after the monuments were installed. A later resurvey of 4 sites showed that some sites with higher subsidence may be unstable, but we consider the subsidence pattern of all the sites. Sites with rates <2 mm/yr overlie thin (≤35 m), sandy Holocene deposits located along interfluves between the main paleo-river valleys. As Holocene strata thicken seaward and become muddier, subsidence rates increase to 20–25 mm/y. Sites in incised valleys of the Ganges, Brahmaputra and Meghna Rivers, with Holocene sediments >100 m show subsidence rates of 20 ± 10 mm/y, with a slight seaward increase. Overall, subsidence rates increase with Holocene sediment thickness and the seaward shift from sandy to muddy sediments. Together with earlier measurements, we parse the different rates and mechanisms of subsidence. Earlier models show 2–3 mm/yr correspond to deep processes, such as isostasy. Within the shallow Holocene (<10 m), we estimate 5–8 mm/yr of subsidence from shallow, edaphic effects (tree roots, burrows, organic matter decomposition) and shallow (≤10 m) sediment consolidation on short timescales. Below this, we estimate 3–6 mm/yr from compaction of the upper Holocene strata, with 2–5 mm/yr occurring in deeper Holocene strata. Subsidence rates in areas of active sedimentation, such as rice fields and mangrove forests, are greater than buildings and structures with deep foundations. Subsidence on timescales >300 y, which do not include edaphic effects, are up to ∼5 mm/y. We note subsidence can be offset by active deltaic sedimentation, and does not necessarily indicate elevation loss. Collectively, the integration of these approaches allows us to begin quantifying the varied contributions to land subsidence from edaphic effects, Holocene sediment compaction, lithology, and time. Similar factors may contribute to the highly variable subsidence rates observed at other deltas worldwide.

We produced a 10 Myr synthetic stratigraphic section using a forward stratigraphic model that generates marine deltaic stratigraphy over geological timescales. We recursively fit the model using a Bayesian inversion algorithm to test: (1) if it could be accurately reconstructed; (2) if the parameters used to create it could be recovered; and (3) the sensitivity of the model output to given model parameters and the attendant physical processes. The original synthetic stratigraphic section was produced with cyclical sea-level variations of 40 and 30 m with 2.4 and 10 Myr periods respectively. Sediment was also supplied cyclically, in 2.4 and 10 Myr cycles with amplitudes of 30 and 80 tons/100 kyr, respectively, varying from a mean of 232 tons/100 kyr. Parameter values were sampled to fit the model using a Markov chain Monte Carlo algorithm, resulting in a +/- 5 m (1 sigma) variation between the experimental output and the original. Sea level varied by +/- 7 m (1 sigma) within the posterior distribution of parameters. As a result, both the 10 Myr and 2.4 Myr sea-level cycles could be extracted from the original output. The variation in sediment supply was approximately +/- 38 tons/100 kyr (1 sigma) and, as a result, only the larger long-term supply variations could be accurately recovered in refitting the model. The variation in thermal, flexural and total subsidence across those parameter sets is less than +/- 10 m (1 sigma). The original section experienced 150 m of total subsidence at the depocentre. Our results demonstrate the distinct and interpretable imprint of sea level and subsidence on continental margin stratigraphy can be quantified. Moreover, we conclude that sea-level change produces a defined effect on the geometries of stratigraphic architecture, and that techniques applied for the purpose of delineating sea-level variation from continental margin strata have a well-founded conceptual basis. Modelledstratigraphy reconstructed using Bayesian inversion. The top panels show the reconstructedstratigraphy (panel a) and a wheeler diagram of this model output (panel b). Thethree other panels show the original and reconstructed values of: 1) flexure,thermal subsidence, and total subsidence (panel c); 2) sea-level change (paneld); and 3) sediment supply variations (panel e). The greater variability in theposterior distribution of sediment supply values relative to those for sealevel suggests that the development of passive continental margin stratigraphic architecture is particularlysensitive to sea-level variation.image

The principal nature-based solution for offsetting relative sea-level rise in the Ganges-Brahmaputra delta is the unabated delivery, dispersal, and deposition of the rivers' ~1 billion-tonne annual sediment load. Recent hydrological transport modeling suggests that strengthening monsoon precipitation in the 21st century could increase this sediment delivery 34-60%; yet other studies demonstrate that sediment could decline 15-80% if planned dams and river diversions are fully implemented. We validate these modeled ranges by developing a comprehensive field-based sediment budget that quantifies the supply of Ganges-Brahmaputra river sediment under varying Holocene climate conditions. Our data reveal natural responses in sediment supply comparable to previously modeled results and suggest that increased sediment delivery may be capable of offsetting accelerated sea-level rise. This prospect for a naturally sustained Ganges-Brahmaputra delta presents possibilities beyond the dystopian future often posed for this system, but the implementation of currently proposed dams and diversions would preclude such opportunities.

The Indo-Burma subduction zone is a highly oblique subduction system where the Indian plate is converging with the Eurasian plate. How strain is partitioned between the Indo-Burma interface and upper plate Kabaw Fault, and whether the megathrust is a locked and active zone of convergence that can generate great earthquakes are ongoing debates. Here, we use data from a total of 68 Global Navigation Satellite System (GNSS) stations, including newly installed stations across the Kabaw Fault and compute an updated horizontal and vertical GNSS velocity field. We correct vertical rates for fluctuating seasonal signals by accounting for the elastic response of monsoon water on the crust. We model the geodetic data by inverting for 11,000 planar and non-planar megathrust fault geometries and two geologically viable structural interpretations of the Kabaw Fault that we construct from field geological data, considering a basin-scale wedge-fault and a crustal-scale reverse fault. We demonstrate that the Indo-Burma megathrust is locked, converging at a rate of 11.6 +/- 5.4 mm/yr, and capable of hosting >8.2 M-w megathrust events. We also show that the Kabaw Fault is locked and accommodating strike-slip motion at a rate of 8.4 +/- 3.0 mm/yr and converging at a rate of 5.7 +/- 4.1 mm/yr. Our interpretation of the geological, geophysical, and geodetic datasets indicates the Kabaw Fault is a crustal-scale structure that actively absorbs a portion of the convergence previously ascribed to the Indo-Burma megathrust. This reveals a previously unrecognized seismic hazard associated with the Kabaw Fault and slightly reduces the estimated hazard posed by megathrust earthquakes in the region. Plain Language Summary Subduction zones are plate boundaries where two tectonic plates converge and can generate large earthquake along its main fault, the megathrust. Earthquakes rupture on faults that remain locked and accumulate strain during the interseismic period, the period of time between great earthquakes. The Indo-Burma subduction zone, where the Indian plate is converging with the Eurasia plate, is home to more than 200 million people. In spite of its enormous population, it is unclear whether the Indo-Burma subduction zone can generate large megathrust earthquakes. To evaluate its potential to host great earthquakes, we combine new GPS datasets that record plate motion during the interseismic period with geological analysis of the Kabaw Fault, one of the secondary faults in the Indo-Burma subduction zone. We demonstrate that Indo-Burma megathrust and Kabaw Fault are locked and can generate significant earthquakes. For the first time, we show that the Kabaw Fault absorbs a portion of the convergence previously ascribed to the Indo-Burma megathrust which could explain the long repeat time between great earthquakes on the megathrust.

Floods cause large losses to property, life, and livelihoods across the world every year, hindering sustainable development. Safety nets to help absorb financial shocks in disasters, such as insurance, are often unavailable in regions of the world most vulnerable to floods, like Bangladesh. Index-based insurance has emerged as an affordable solution, which considers weather data or information from satellites to create a "flood index" that should correlate with the damage insured. However, existing flood event databases are often incomplete, and satellite sensors are not reliable under extreme weather conditions (e.g., because of clouds), which limits the spatial and temporal resolution of current approaches for index-based insurance. In this work, we explore a novel approach for supporting satellite-based flood index insurance by extracting high-resolution spatio-temporal information from news media. First, we publish a dataset consisting of 40,000 news articles covering flood events in Bangladesh by 10 prominent news sources, and inundated area estimates for each division in Bangladesh collected from a satellite radar sensor. Second, we show that keyword-based models are not adequate for this novel application, while context-based classifiers cover complex and implicit flood related patterns. Third, we show that time series extracted from news media have substantial correlation Spearman's rho=0.70 with satellite estimates of inundated area. Our work demonstrates that news media is a promising source for improving the temporal resolution and expanding the spatial coverage of the available flood damage data.

Remotely sensed data have the potential to monitor natural hazards and their consequences on socioeconomic systems. However, in much of the world, inadequate validation data of disaster damage make reliable use of satellite data difficult. We attempt to strengthen the use of satellite data for one application—flood index insurance—which has the potential to manage the largely uninsured losses from floods. Flood index insurance is a particularly challenging application of remote sensing due to floods’ speed, unpredictability, and the significant data validation required. We propose a set of criteria for assessing remote sensing flood index insurance algorithm performance and provide a framework for remote sensing application validation in data-poor environments. Within these criteria, we assess several validation metrics—spatial accuracy compared to high-resolution PlanetScope imagery (F1), temporal consistency as compared to river water levels (Spearman's ρ), and correlation to government damage data (R2)—that measure index performance. With these criteria, we develop a Sentinel-1 flood inundation time series in Bangladesh at high spatial (10 m) and temporal (∼weekly) resolution and compare it to a previous Sentinel-1 algorithm and a Moderate Resolution Imaging Spectroradiometer (MODIS) time series used in flood index insurance. Results show that the adapted Sentinel-1 algorithm (F1avg = 0.925, ρavg = 0.752, R2 = 0.43) significantly outperforms previous Sentinel-1 and MODIS algorithms on the validation criteria. Beyond Bangladesh, our proposed validation criteria can be used to develop and validate better remote sensing products for index insurance and other flood applications in places with inadequate ground truth damage data.