arXiv subjects

Gabriele Bertoli

Publications and source records attributed to Gabriele Bertoli.

3 recordsLinked to original sources

arXiv2026

A Dataset and Model for Imputing Water Surface Elevation on a Large and Extremely Sparse Spatiotemporal Graph

Continuous monitoring of water surface elevation across river networks is critical for flood forecasting, water resource management, and understanding the global water cycle. Yet, the scarcity of in situ gauges across much of the globe constrains the development of reliable modeling frameworks. Satellite altimetry has the potential to alleviate this problem but its use is currently hindered by sparse temporal coverage. To this end, we introduce AmazonSWE, a dataset for training and evaluating large-scale spatiotemporal graph imputation methods that integrates processed satellite altimetry measurements from a range of sources, including the recent wide-swath SWOT sensor. The dataset covers over 19K river sections and 10 years (2016-2026) in the Amazon river basin, with in situ gauges held out for evaluation. Besides contributing a novel real-world use case with the potential for societal impact, AmazonSWE introduces significant technical challenges: with fewer than 1% of sections observed per day, the dataset is far sparser than existing imputation benchmarks, and its directed acyclic river topology is both structurally different from and larger than graphs in existing datasets. We show that prior spatiotemporal graph imputation methods are not adapted to this topology, scale and sparsity, and propose a simple bidirectional selective state space model that outperforms them by sampling connected subgraphs and flattening space and time into a single token sequence with topology-aware positional encodings. Compared to the state-of-the-art published method for SWOT-based WSE densification, which integrates statistics with physical modeling, our model reduces RMSE against in situ gauges by 18-39%, while producing predictions for every river section rather than only those with sufficient nearby satellite coverage.

cs.LG↗

arXiv2026

A Hybrid Machine Learning Framework for Improved Short-Term Peak-Flow Forecasting

Reliable river flow forecasting is an essential component of flood risk management and early warning systems. It enables improved emergency response coordination and is critical for protecting infrastructure, communities, and ecosystems from extreme hydrological events. Process-based hydrological models and purely data-driven approaches often underperform during extreme events, particularly in forecasting peak flows. To address this limitation, this study introduces a hybrid forecasting framework that couples Extreme Gradient Boosting (XGBoost) and Random Forest (RF). XGBoost is employed for continuous streamflow forecasting, while RF is specifically trained for peak-flow prediction, and the two outputs are combined into an enhanced forecast. The approach is implemented across 857 catchments of the LamaH-CE dataset, using rainfall and discharge observations at 6-hour resolution. Results demonstrate consistently high skill, with 71% of catchments achieving a Kling-Gupta Efficiency (KGE) greater than 0.90. Peak-flow detection reaches 87%, with a false-alarm rate of 13%. Compared to the European Flood Awareness System (EFAS), the framework achieves lower peak-magnitude errors, fewer false alarms, and improved streamflow and peak-flow forecasting accuracy. The proposed framework is computationally lightweight, scalable, and easily transferable across watersheds, with training times of only seconds on standard CPUs. These findings highlight the potential of integrating hydrological understanding with efficient machine learning to improve the accuracy and reliability of operational flood forecasting, and outline future directions for hybrid hydrological-machine learning model development.

eess.SP↗

arXiv2023

How effective is multifactor authentication at deterring cyberattacks?

This study investigates the effectiveness of multifactor authentication (MFA) in protecting commercial accounts from unauthorized access, with an additional focus on accounts with known credential leaks. We employ the benchmark-multiplier method, coupled with manual account review, to evaluate the security performance of various MFA methods in a large dataset of Microsoft Azure Active Directory users exhibiting suspicious activity. Our findings reveal that MFA implementation offers outstanding protection, with over 99.99% of MFA-enabled accounts remaining secure during the investigation period. Moreover, MFA reduces the risk of compromise by 99.22% across the entire population and by 98.56% in cases of leaked credentials. We further demonstrate that dedicated MFA applications, such as Microsoft Authenticator, outperform SMS-based authentication, though both methods provide significantly enhanced security compared to not using MFA. Based on these results, we strongly advocate for the default implementation of MFA in commercial accounts to increase security and mitigate unauthorized access risks.

cs.CR↗