Does cloud seeding actually increase rainfall?

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1. 1

   Structured dataset of reported cloud seeding activities in the United States (2000-2025) using an LLM.

   Scientific data (Donohue & Lamb)Published Dec 11, 2025Checked Oct 7, 2026

   “Cloud seeding, a weather modification technique used to increase precipitation, has been practiced in the western United States since the 1940s. However, comprehensive datasets are not currently available to analyze these efforts. To address this gap, we present a structured dataset of reported cloud seeding activities in the U.S. from 2000-2025, including the project name, year, season, state, operator, seeding agent, apparatus used for deployment, stated purpose, target area, control area, start date, and end date. Combining our multi-stage PDF-to-text extraction pipeline with OpenAI's o3 large language model (LLM), we processed 832 historical reports from the National Oceanic and Atmospheric Administration (NOAA). The resulting dataset demonstrates 98.38% estimated accuracy, based on manual review of 200 randomly sampled records, and is publicly available on Zenodo. This dataset addresses the gap in cloud seeding data and demonstrates the potential for LLMs to extract structured information from historical environmental documents. More broadly, this work provides a scalable framework for unlocking historical data from scanned documents across scientific domains.”

2. 2

   Precipitation formation from orographic cloud seeding.

   Proceedings of the National Academy of Sciences of the United States of America (French et al.)Published Jan 22, 2018Checked Oct 7, 2026

   “The intent of glaciogenic seeding of orographic clouds is to introduce aerosol into a cloud to alter the natural development of cloud particles and enhance wintertime precipitation in a targeted region. The hypothesized chain of events begins with the introduction of silver iodide aerosol into cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals, followed by ice particle growth to sizes sufficiently large such that snow falls to the ground. Despite numerous experiments spanning several decades, no direct observations of this process exist. Here, measurements from radars and aircraft-mounted cloud physics probes are presented that together show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic seeding. These data, by themselves, do not address the question of cloud seeding efficacy, but rather form a critical set of observations necessary for such investigations. These observations are unambiguous and provide details of the physical chain of events following the introduction of glaciogenic cloud seeding aerosol into supercooled liquid orographic clouds.”

3. 3

   Quantifying snowfall from orographic cloud seeding.

   Proceedings of the National Academy of Sciences of the United States of America (Friedrich et al.)Published Feb 24, 2020Checked Oct 7, 2026

   “Here, a physically based approach to quantify snowfall from cloud seeding in mountain cloud systems is presented. Areas of precipitation unambiguously attributed to cloud seeding are isolated from natural precipitation (-1). Spatial and temporal evolution of precipitation generated by cloud seeding is then quantified using radar observations and snow gauge measurements. This study uses the approach of combining radar technology and precipitation gauge measurements to quantify the spatial and temporal evolution of snowfall generated from glaciogenic cloud seeding of winter mountain cloud systems and its spatial and temporal evolution. The results represent a critical step toward quantifying cloud seeding impact. For the cases presented, precipitation gauges measured increases between 0.05 and 0.3 mm as precipitation generated by cloud seeding passed over the instruments. The total amount of water generated by cloud seeding ranged from 1.2 × 105 m3 (100 ac ft) for 20 min of cloud seeding, 2.4 × 105 m3 (196 ac ft) for 86 min of seeding to 3.4 x 105 m3 (275 ac ft) for 24 min of cloud seeding.”

4. 4

   Glaciogenic Seeding of Cold-Season Orographic Clouds to Enhance Precipitation: Status and Prospects

   Bulletin of the American Meteorological Society (Geerts & Rauber)Published Jul 21, 2022Checked Oct 7, 2026

   “Randomized seeding experiments have a solid statistical foundation and focus on the outcome, but, in light of the small seeding signal and the naturally noisy nature of precipitation, they generally require too many cases to be affordable, and therefore are discouraged. A complementary method, physical evaluation, examines changes in cloud and precipitation processes when seeding material is injected and yields insights into the most suitable ambient conditions. Recent physical evaluations have established a robust, well-documented scientific basis for glaciogenic seeding of cold-season orographic clouds to enhance precipitation. The challenge of seeding impact assessment remains, but evidence is provided that, thanks to recent significant progress in observational and computational capabilities, the research community is finally on track to be able to provide stakeholders with guidance on the likely quantitative precipitation impact of cloud seeding in their region. We recommend further process-level evaluations combined with highly resolved, well-constrained numerical simulations of seasonal cloud seeding.”

5. 5

   Review of Advances in Precipitation Enhancement Research

   Bulletin of the American Meteorological Society (Flossmann et al.)Published Apr 2, 2019Checked Oct 7, 2026

   “This paper provides a summary of the assessment report of the World Meteorological Organization (WMO) Expert Team on Weather Modification that discusses recent progress on precipitation enhancement research. The progress has been underpinned by advances in our understanding of cloud processes and interactions between clouds and their environment, which, in turn, have been enabled by substantial developments in technical capabilities to both observe and simulate clouds from the microphysical to the mesoscale. We focus on the two cloud types most commonly seeded in the past: winter orographic cloud systems and convective cloud systems. A key issue for cloud seeding is the extension from cloud-scale research to water catchment–scale impacts on precipitation on the ground. Consequently, the requirements for the design, implementation, and evaluation of a catchment-scale precipitation enhancement campaign are discussed. The paper concludes by indicating the most important gaps in our knowledge. Some recommendations regarding the most urgent research topics are given to stimulate further research.”

6. 6

   Advances in the Evaluation of Cloud Seeding: Statistical Evidence for the Enhancement of Precipitation

   Earth and Space Science (Wu et al.)Published Sep 1, 2018Checked Oct 7, 2026

   “We describe important issues, aiming to reduce systematic errors and uncertainties in statistical tests as well as increase the level of quantitative sounding and evaluation. First, a regularized set of design and operation in the steps should be established to optimize techniques of cloud seeding. Second, the latest achievements in atmospheric physics, physical sounding, and statistics need to be introduced to help improve the correctness and scientificity. Third, middle‐ and long‐term special research projects are expected to investigate the influence of ideal hypotheses of seeding schemes, statistical test plans, and statistical methods. These demands can update our knowledge and technology of weather modification and increase the cooperation of multidiscipline, such as logical integration of statistical tests, physical analysis, and numerical modeling.”