Weather Modification and Local Climate Management in the United States: A Review of Its Technological Evolution, Operations, Governance, and Local Implementation Challenges

Abstract

Weather modification has gained significant and growing interest in the United States (US) in recent years. The trend can be largely attributed to the changing climate, persistent droughts, and other extreme weather events that have been experienced across various regions of the US. This paper provides a critical review of weather modification program costs, benefits, policy, and governance to help shed light on policymaking and program management associated with the growing interest in adopting weather modification as a local climate management strategy in the US. Additionally, to deepen our understanding of the widely concerning issues, such as the financial burden on taxpayers and potential environmental risks, the paper explored the local implementation challenges and common environmental and public health concerns related to weather modification activities. A synthesis of the literature and policy debates reached four general conclusions: (1) The need for weather modification programs is expected to keep growing, though regional variations may exist due to regulatory and other local factors; (2) weather modification can bring significant local benefits, ranging from enhanced agricultural yield and recreational economy to extreme weather management and public environmental health benefits; (3) state-level and local support, including financial resources, will be essential for program development in the foreseeable future; and (4) technological advancements will be critical for addressing many of the project operation efficiency challenges and environmental and public health concerns related to weather modification programs. More specifically for program governance and local implementation, aspects such as project planning (including resource pooling), risk and liability management, communication and reporting, outcome measurability, and stakeholder engagement are indispensable for addressing issues related to program legality and oversight, public acceptance, and sustainability.

1. Introduction

Weather modification refers to the temporary local or regional alteration of weather conditions through human intervention. As a local climate management strategy, it has been around for over a century in the United States (US). While operating technology has evolved over the past century, its main applications stay the same, ranging from precipitation enhancement to extreme weather management (e.g., hail suppression and fog dispersion). Among these application scenarios, precipitation enhancement is the most common purpose of weather modification. It is also why, in many cases, cloud seeding—a standard rain and snow enhancement operation—is used interchangeably with weather modification. In recent decades, as drought becomes more persistent in the US West and Southwest [1], weather modification operations have regained attention among practitioners and on policy agendas (e.g., [2,3]). Figure 1 shows the number of weather modification project reports filed with the National Oceanic and Atmospheric Administration (NOAA) by proposed project start year. Most of these reports were filed by western states. The surge of the number of project reports in recent years suggests a growing interest in adopting weather modification as a drought management strategy. However, cloud seeding can be an expensive operation. Taking cloud seeding in agricultural regions as an example, operating a weather modification program throughout the growing season can cost from several hundred thousand dollars to several million dollars, depending on the size of the operation region and other local factors [4]. Meanwhile, studies have shown that the high operating costs of weather modification programs can be easily justified by the resulting benefits in agricultural outcomes (e.g., [5]). From a cost–benefit perspective, it has been a widely accepted local climate management strategy. Figure 2 shows the recent surge of interest in learning about cloud seeding and weather modification in the US based on web search interest data collected by Google Trends 2025.

At the technological level, new advancements have helped improve operational and cost efficiencies of cloud seeding programs. Traditionally, manned small aircraft are the main operating platform for cloud seeding activities. Recently, the development of drone technologies and cloud-based data solutions has enabled additional operational flexibility and room for efficiency improvement in cloud seeding [6]. The new development also allows for more accurate and coordinated data collection during operations, taking advantage of the (drone-based) distributed system, which capacitates advanced data analytics to improve future operation effectiveness. Despite all the advancements in operating efficiency and technology, the growing adoption of weather modification in agriculture and other sectors (e.g., disaster management and recreation) comes with concerns and debates. Concerns and debates about weather modification programs focus on two aspects: potential environmental impacts and public health uncertainty. For instance, some public have confused local weather modification with solar geoengineering, while the US Environmental Protection Agency (EPA) clarifies that “the main difference between weather modification and solar geoengineering is that weather modification is intended to have local, short-term effects, whereas solar geoengineering is intended to have larger regional or global effects that persist [7].” Other federal agencies, such as NOAA, try to stay neutral regarding weather modification programs. NOAA states on its website that “NOAA does not fund or participate in cloud seeding or other weather modification projects,” while the agency does acknowledge the widespread existence of weather modification projects in the Mountain West and Desert Southwest regions [8]. At the state level, several states recently passed state laws banning weather modification activities, including Florida and Tennessee. For example, Florida Senate Bill 56, signed into state law in June 2025, prohibits traditional weather modification and solar geoengineering programs (see https://www.flsenate.gov/Session/Bill/2025/56, accessed on 4 September 2025). Meanwhile, other conservative states, such as Arizona, passed similar legislation but exempted weather modification programs from the regulation. Overall, the center of the policy debates behind these legislative efforts is not necessarily on the effectiveness of weather modification, but more on the general legality of solar geoengineering activities and if local weather modification should be considered a solar geoengineering activity.

Given these environmental and policy contexts, the goal of this review is to look into the cost, benefit, and governance aspects of weather modification programs in the US and shed light on (1) the policy debate related to the legality of weather modification activities, (2) the local implementation challenges of weather modification programs, and (3) how to understand and address their potential environmental impacts. A synthesis of these different aspects helps stakeholders to better understand the benefits and costs of weather modification programs. It also helps the scientific and policy research communities to identify directions of future research concerning program governance, technology gap, seeding materials and methods, and the need for more case studies. On the whole, we argue that weather modification brings both opportunities and challenges to local climate and extreme weather event management. From a project management perspective, it is critical to consider community perception and various project risks, and develop implementation plans accordingly. Before delving into cost, benefit, and program governance, we first provide an overview of weather modification concepts, history, and its technological evolution in the US.

2. Concepts, History, and Technological Evolution

Weather modification is an activity combining desired atmospheric conditions and spatial-temporally targeted management of a primarily physical process. The common purpose of weather modification activities is to enhance precipitation (rainfall and snow) to supplement water supply for agricultural irrigation and ecosystem health, especially in arid and semi-arid areas. Additionally, weather modification is a common strategy for managing disastrous weather (e.g., hail and fog) and precipitation enhancement for non-agricultural purposes (e.g., snowmaking at recreational resorts). In the US, the most common weather modification activity is cloud seeding for precipitation enhancement [8]. Technically, cloud seeding is a process of dispersing substances (i.e., cloud seeding agents) into clouds to generate ice nuclei inside the clouds and induce precipitation. Figure 3 illustrates a typical cloud seeding process for precipitation enhancement in an agricultural setting.

Americans have practiced cloud seeding for over a century. In early times, without aircraft, people could only disperse cloud seeding agents from the ground. In 1915, the City of San Diego hired Charles Hatfield, a moisture accelerator, to conduct a cloud seeding project during a major drought. Hatfield built a 20-foot tower and burned chemical mixtures from the top of the structure to create rain [9]. In this experimental application, while it rained, the rainfall only covered certain areas. Yet drought situations happen in different places and potentially larger areas. Thus, having the flexibility to manage droughts through cloud seeding operations in targeted places becomes necessary. The invention of aircraft in the early 20th century made an alternative solution possible. Small aircraft can help carry seeding agents and disperse them more precisely and effectively. It has since motivated continued innovation in cloud seeding technologies.

Innovation in cloud seeding materials (agents) was another key aspect in driving the development of weather modification technologies. Scientists at General Electric Co. (GE; Schenectady, NY, USA) were the first group to systematically experiment with cloud sending agents in the 1940s [10]. They first used dry ice as a seeding agent, given that it can absorb heat from its surroundings and thus lower the nearby temperature. Schaefer found through lab-scale experiments that when dry ice presents the supercooled clouds in the chamber are completely converted to ice crystals [11]. A later experiment shows that seeding dry ice in large cumulus clouds in summer can generate heavy rains within fifteen to twenty minutes after releasing [12].

Meanwhile, there were efficiency concerns about using dry ice for cloud seeding. In the cloud seeding process, aircraft need to carry agents into the sky and disperse them into target clouds. However, it is costly to bring large amounts of dry ice into the air due to its weight. Moreover, dry ice is typically divided into small pellets one-third to three-quarters of an inch in diameter for dispersion [13]. Their weight forces them to follow certain paths after being dispersed, different from other powder-like substances. The reason is that air makes an upward force, and the air resistance force is less significant for heavier objects. This can lead to uneven dispersion of dry ice pellets, over-seeding in some areas, and under-seeding in others. Such uneven dispersion of seeding agents reduces the efficiency of weather modification and can increase operating costs.

As practitioners continued searching for alternative and better sending agents, Vonnegut conducted experiments with silver iodide as a seeding agent [14]. He found that silver iodide’s physical structure closely resembles the structure of ice, and thus it is effective at forming ice crystals in supercooled clouds. His finding was pivotal in the development of cloud seeding technology because clouds are composed of numerous supercooled water drops. Following his experiment, silver iodide has been widely used for cloud seeding. Nowadays, silver iodide is the most common cloud seeding agent. There are two additional reasons for its dominance in seeding materials. First, silver iodide particles are small, with a size similar to that of smoke particles. This increases its contact time and surface area in clouds, which helps precipitate ice crystals more effectively. Merely one gram of silver iodide can precipitate up to 10 trillion artificial ice crystals [15]. Second, since aircraft need to carry cloud seeding agents into the air for dispersion, it is more economical to use silver iodide due to its lighter weight, and hence smaller amounts are needed. All these advantages make silver iodide a cost-effective material for cloud seeding, which explains its growing popularity in cloud seeding applications.

As cloud seeding technologies quickly spread, it became necessary to assess their effectiveness and impacts for program development and policymaking purposes. For example, Huff and Changnon studied the potential effects of modifying growing-season rainfall on the yields and economic benefits of corn and soybeans in Illinois with hypothetical cloud seeding models [16]. Their hypothetical cloud seeding experiments adopted statistical sampling designs, which also drew attention from professional statisticians. For example, Neyman focused on issues related to the design of regression methods and randomization in evaluations of weather modification projects [17]. Gabriel and Hsu studied computations of power of re-randomization tests, with applications to weather modification experiments [18].

Recent technological advancements in unmanned aircraft systems (UAS) have led to further improvements in weather modification operations. UAS are very helpful from two aspects. First, they can collect detailed data about atmospheric conditions to assist with cloud seeding planning and implementation. The USDOE documents suggest that such data can include air temperature, pressure, and humidity, and the data can even be obtained from hard-to-reach places with UAS [19]. In addition, UAS can carry specialized scientific instruments to collect data on the cloud system dynamics and its colloidal stability [20]. Such information can be valuable for further enhancing the accuracy and efficiency of cloud seeding. Second, UAS can be used to conduct cloud seeding operations more efficiently. Compared to a manned aircraft, UAS are automated and are more accurate in cloud seeding operations [20]. It helps improve the targeting accuracy and hence the operating efficiency of cloud seeding. UAS also provide an alternative tool for cloud seeding when weather conditions are unsafe for larger aircraft-based operations.

UAS-based operations also have potential downsides. UAS are smaller than manned aircraft. For instance, Manta (manufactured by Northrop Grumman in Falls Church, VA, USA), a small unmanned aircraft used by NOAA’s Pacific Marine Environmental Laboratory, only has a 6.8 kg payload, while seeding a cloud system can require over 200 kg of seeding agents [20]. The capacity limitation of UAS restricts the amount of cloud seeding agents that they can carry during an operation. When the target seeding area is large, a UAS-based operation requires either more trips or more drones compared to manned aircraft.

Table 1. A comparison of manned aircraft and UAS in cloud seeding applications.

Category	Manned Aircraft	UAS
Operation Capacity	Can carry and apply more cloud seeding agents in one operation	Require multiple trips if large amounts of cloud seeding agents are needed
Data Collection	Can only collect data in reachable places	Can collect data in hard-to-reach places and in potentially high resolution
Operation Requirements	Require human operators; Require safe weather conditions to operate	Use automated system to improve accuracy; can remain in operation under harsh weather conditions
Major Operating Costs	Aircraft leasing cost, operator wage, fuel cost, customized weather data cost, seeding materials	UAS equipment cost, operator wage, battery and electricity costs, customized weather and other data services, seeding materials
Technical Support Requirements	Little to none needed if assuming no maintenance for leased aircraft	Drone operation algorithm development; drone maintenance

presents a comparison of manned aircraft and UAS in cloud seeding operations. It is clear that traditional manned aircraft have advantages in capacity and technical support requirements. UAS-based operations dominate in other aspects, including data collection, operation requirements, and operating costs.

Despite the fact that ground-based cloud seeding method is not popular among key applications (e.g., agriculture and hail suppression) in the US, it is commonly used for snowpack enhancement in wintertime and it has also experienced some technological advancements. In particular, remote sensing and data analytics have been deployed to improve operational monitoring and seeding precision (e.g., see [21]). Because of the growing role of data analytics in weather modification operations across technology, it is highly possible to integrate ground-based approach and UAS-based approach in the future to improve seeding effectiveness and manage operation costs and environmental impacts. In practice, advanced ground-based cloud seeding methods have been developed in the US West. The Santa Ana River Watershed Cloud Seeding Pilot Program in California is a recent example of this (https://sawpa.gov/santa-ana-river-watershed-cloud-seeding/, accessed on 10 January 2026). With a project goal to increase snowpack and water supply for the entire watershed, it combines remotely controlled seeding equipment with manually operated generators to improve seeding effectiveness and optimize operation costs.

3. Operation Costs

Weather modification programs incur significant costs, including fixed capital costs and variable costs. Fixed costs are expenses that do not change with respect to the amount of provided services. One typical expense is the aircraft if it is owned by the program. However, programs that need aircraft for cloud seeding usually rent an aircraft for the period of operations or contract out the operation entirely. Variable costs are expenses that change with respect to the amount of services provided. Such expenses include costs for acquiring cloud seeding materials, aircraft service contracts (that cover fuels and pilot hours), and necessary technical services (e.g., customized weather reports). Between the two types of costs, aircraft-related costs take up a major portion. For example, a 2024 Flying Magazine article records that the average rental rate of a Turboprop aircraft (its balance of fuel efficiency and performance makes it suitable for short to medium-range flights and operations; ideal for cloud seeding in large areas) is $1000–$3000 per hour [22]. This is also why a UAS-based operation could offer significant cost advantages for cloud seeding.

Given the high costs of weather modification operations, many projects are implemented at large spatial scales for cost efficiency. This also allows weather modification programs to seek extramural funding for program support. For example, recently, a $2.4 million federal grant was awarded to support cloud seeding projects in the Upper Colorado River Basin [23]. Utah state legislature appropriated $12 million in one-time funding to support seven active cloud seeding project areas in 2023, with $5 million for operational funding as the program moves forward [24]. Due to the high operation cost, smaller areas in need of weather modification services find it difficult to adopt them as a strategy to manage drought and extreme weather events. They need to collaborate to pool resources and share the costs of program operations, especially the aircraft-related costs. This explains why weather modification is often implemented on a large scale across the US. Additionally, recent assessments of cloud seeding projects in the US suggest that regional cloud seeding programs are cost-effective, with estimated benefit–cost ratios of at least 5:1 (e.g., see [25,26]).

To address the operation cost challenge, technological advancements in UAS bring at least two advantages. First, UAS-based technologies offer higher cost efficiency. They help address the cost barrier and allow smaller areas to implement cloud seeding. The operation costs of UAS are significantly lower than those of manned aircraft. Additionally, given that UAS are much smaller than manned aircraft, they carry fewer seeding agents than manned aircraft. While this is a disadvantage for large-scale weather modification operations, it is well-suited for smaller projects that require fewer seeding agents. From an energy efficiency perspective, with fewer seeding agents onboard (less takeoff weight), energy costs are lower. The new UAS-based technology has gained producers’ attention in practice, leading to active experimentation. For instance, scientists at the Desert Research Institute in Reno, Nevada, successfully implemented the world’s first cloud-seeding exercise with an octocopter drone in 2016 [27]. More recently, Utah water resources managers tested drone-based cloud seeding when a storm passed through the Cache Valley [28].

Second, UAS-based weather modification operations offer the possibility of integrating other advanced agriculture management technologies, such as precision agriculture (e.g., through variable-rate application), with small-area cloud seeding. For example, a precision agriculture management system can collect near-real-time high-precision data on soil moisture through remote sensing of evapotranspiration (ET; e.g., see OpenET at https://etdata.org/), which provides useful analytics of drought conditions and irrigation needs. A UAS-based weather modification operation can then transform these near-real-time data into spatially targeted cloud seeding operations, achieving desired precipitation outcomes and enhanced project cost efficiency.

Additionally, the development of artificial intelligence (AI) could further improve the precision of weather modification, which also helps reduce costs. During a weather modification operation, the aircraft or drone needs to disperse cloud seeding agents into target clouds. Accurately predicting weather and cloud movements is critical for dispersing seeding agents effectively. The development of AI solutions helps achieve this goal. First, machine learning models can analyze a large amount of meteorological data to predict local weather conditions and identify the most favorable opportunities for cloud seeding [29]. For example, Bi et al. show that three-dimensional deep networks equipped with data-driven priors are effective at recognizing complex patterns in weather data with reduced errors in medium-range forecasting [30]. These AI techniques can greatly enhance the accuracy and efficiency of cloud seeding. Second, AI can mobilize real-time data from sensors installed on aircraft and make necessary adjustments during the operation. For example, DeFelice et al. conducted the first demonstration of UAS for operational rain enhancement [31]. Their study shows that UAS with cloud sensors and autonomous-adaptive control technology have the potential for improved targeting efficiency and seeding effectiveness. Such improved accuracy can reduce unnecessary aircraft or drone trips and lower weather modification operation costs.

Lastly, it is worth noting that the cost efficiency of a weather modification program can also be measured by its precipitation outcome. For instance, the California Department of Water Resources estimates that the cost of cloud seeding-induced precipitation is between $20 to $40 per acre foot depending on the location [32]. It provides an alternative way to justify the cost efficiency of a weather modification program when assessing program operation costs. This leads to a necessary discussion of weather modification project benefits, which is the focus of the next section.

4. Project Benefits

Investment in weather modification programs creates benefits through several channels. First and foremost, weather modification increases precipitation. This is valuable for agricultural production, especially during persistent drought periods. Additional rainfall from weather modification can reach up to 20% of the water supply in many cases [33]. As a result, increased precipitation improves crop yields. For example, Knowles and Skidmore found that wheat in counties that participated in the North Dakota Cloud Modification Project yielded 3.87 bushels more per harvested acre (a 13% increase) compared to non-participating counties [26]. Yield increases in turn improve farmers’ income. Given that the wheat price in North Dakota in July 2021 was $7.76 per bushel according to the USDA [34], farmers in counties that participated in weather modification received about $30 more per harvested acre (or about $46,000 per farm, given an average farm size of 1537 acres in North Dakota). Besides its application in agriculture, enhanced precipitation by weather modification is also valuable for recreational purposes. Ski resorts are a common beneficiary. For example, the Wyoming Water Development Commission found that cloud seeding could boost snowfall by 5–15% [35]. According to Falk, a 10% increase in snow thickness could bump the number of tourist overnight stays by at least 0.5% [36]. Furthermore, increased precipitation through weather modification can reduce air pollution, which is beneficial to respiratory health. For instance, precipitation can remove soot, sulfates, and organic particles in the air [37]. This benefit has been exercised by countries such as India and China to promote public environmental health [33].

In addition to precipitation and related benefits, weather modification can be used to manage extreme weather events, such as defogging and hail suppression, which help reduce accidents and casualties. Fog is composed of tiny water drops or ice crystals suspended in the air. It greatly reduces visibility and increases the chance of accidents. For instance, a dense fog west of New Orleans caused a series of crashes involving over 160 vehicles in 2023 [38]. Cloud seeding can be used to dissipate fog by speeding up the condensation of fog droplets. More than half a century ago, Beckwith reported that seeding supercooled fogs by dry ice at airports can improve visibility within an hour, allowing the operations of many scheduled flights that would otherwise be delayed or canceled [39]. In recent years, researchers have continued studying effective fog dissipation. For example, Rohwetter et al. and Wolf have focused on the use of ultra-short laser pulses for weather control, with applications to fog dissipation [40,41].

Another major extreme weather management scenario is hail suppression. Typically formed during thunderstorms, hail is a type of precipitation that contains solid ice. It can break windows, damage properties, and injure humans. Besides its threats to people and their properties, hail is also detrimental to field crops and fruit trees. It can cause significant leaf loss that is difficult for crops and trees to recover from. For instance, losing 50% of leaf area at the R3 growth stage for corn (Milk Stage) is associated with about 20% loss in yield [42]. Safety and financial concerns caused by hail prompt people to find potential solutions. Cloud seeding provides a way to mitigate hail damage by reducing the size of hailstones. When introduced into a cloud, seeding agents form anthropogenic hail embryos to compete with natural hail embryos for supercooled water [43]. As the number of hail embryos increases, on average, there is less cloud water available for each embryo, and thus the size of hailstones becomes significantly smaller. For example, cloud seeding has long been adopted in Alberta, Canada, a region that frequently experiences hailstorms. For example, Gilbert et al. found that two cloud-seeded storms in Alberta had 45.7% and 17.9% smaller impact areas compared to the neighboring areas not seeded [44].

Weather modification can also be useful for other types of disaster management. For instance, wildfire suppression is a possible application scenario, but there are open debates about its applicability and effectiveness. Wildfires can be caused by natural events such as lightning or human activities such as unattended campfires. Due to the warming temperature, the risks of drought and wildfires have become higher in the US West and Southwest in recent decades [45,46]. As a result, cloud seeding induced precipitation has been proposed as a potential solution for wildfire suppression. However, there are at least three concerns about the proposed practice. First, cloud seeding is only effective when there are sufficient clouds. People need to wait for the appropriate weather conditions to implement cloud seeding. But wildfires require immediate attention and quick solutions to keep the situation under control. It can be unrealistic to wait for suitable cloud seeding conditions while wildfires are quickly spreading. Second, while cloud seeding can induce rain from clouds, it may cause unintended consequences. One possibility is that it could induce lightning and cause more fires [47]. Another possibility is that the quick precipitation over fresh burn scars may elevate the risks of floods and soil erosion [48]. Third, there are potential regulatory and liability issues related to using cloud seeding to suppress wildfires. For instance, these issues may include the lack of a uniform cross-boundary regulatory environment and the disproportionate harm to disadvantaged communities [49]. The next section will further explore the legal and regulatory aspects in terms of weather modification program governance.

5. Program Governance

To properly balance the costs and benefits of a weather modification program, its governance is critical. In general, the governance structure for a weather modification program and similar initiatives should consist of at least roles and responsibilities, processes for planning and decision-making, communication and reporting procedures, risk management and accountability, and mechanisms for performance monitoring and assessment. Program governance is beyond the cost–benefit analysis level. It is set up to ensure stakeholder engagement, effective collaborations, program sustainability, and broader societal impacts. In the US, weather modification programs face several key challenges in terms of program governance. The most common challenge comes from the ethical aspect related to roles and responsibilities. There are still lots of uncertainties about the impacts of weather modification on the local environment. As mentioned earlier, weather modification may cause unintended consequences, including lightning, flash floods, and soil erosion. Additionally, silver iodide, a commonly used seeding agent, may negatively influence the local environment. Fajardo et al. studied the continued use of silver iodide for cloud seeding in the same geographical areas [50]. Their study shows that an increasing concentration of silver iodide could negatively affect biota living in terrestrial and aquatic ecosystems. The result contradicts earlier views that the concentration of silver iodide is usually too low to impose significant toxicological effects. The study exemplifies the continuous debate on the possible adverse effects of cloud seeding. It also highlights the importance of clear roles and responsibilities and well-established communication and reporting procedures in program governance.

Another common ethical concern is religion-related. Some religions regard weather as a way for supernatural existence to communicate its will. However, weather modification seeks to alter weather patterns to better align with human needs. As a result, weather modification often receives criticism because it disturbs a supernatural order. For example, Cynthia Crysdale, a Christian ethicist, believes that people should “let nature take its course [51]”. Concerns arising from religious beliefs often contradict the program rationale behind weather modification, which then hinders its local implementation (to be discussed in the next section). For instance, a North Dakota legislator introduced a bill aimed to end weather modification programs and penalize them as a misdemeanor offense based on the belief that God should do what he does among local farmers [52]. Other conservative states proposed similar bills that would ban weather modification [53]. These recent legislative developments suggest the importance of addressing public concerns and highlight the need of inclusive program planning processes, timely reporting, and communication.

In addition to the ethical concerns, there are other important considerations related to project risk, accountability, and potential legal issues. The first important consideration is about property rights. In the US, while land and surface water rights are well established, property rights about clouds and atmospheric water remain unclear. The two key questions are who owns clouds and who owns the water in clouds [54]. Clouds are constantly moved by wind. And there is a time lag between cloud seeding and the beginning of rain. Thus, it is likely that cloud seeding happens in one location while the rain starts in another, which can lead to disputes and liability issues. DeFelice et al. found that downwind areas are more likely to receive the cloud seeding effects, which can be 5–15% increases in precipitation [55]. But these areas are not necessarily within the target seeding areas. The extra precipitation can have two-sided effects. If it is beneficial to the downwind areas, the scenario leads to a free-rider problem as they enjoy the benefits without sharing the costs of cloud seeding. If the extra precipitation becomes excessive and damaging, the scenario leads to potential liability issues, highlighting the importance of risk management and accountability in program governance.

The second important consideration is related to the lack of federal support. There has been little support for weather modification programs at the federal level in the past several decades [56,57]. For example, the Weather Modification Research and Technology Transfer Authorization Act of 2005 (HR 2995), aimed to promote and fund research and development for weather modification programs, failed to become law (see https://www.congress.gov/bill/109th-congress/house-bill/2995, accessed on 4 September 2025). Recently, a new legislative bill (Clear Skies Act of 2025; see https://www.congress.gov/bill/119th-congress/house-bill/4403, accessed on 4 September 2025) was introduced to prohibit weather modification within the US. One consequence due to the lack of federal support is the policy vacuum in governing cross-state weather modification projects. Hence, state governments become the main regulatory entities in such cases [10]. The absence of consistent legal and regulatory frameworks poses barriers to cross-state collaboration, which is necessary for large-scale projects. There is also no federal mechanism for monitoring weather modification activities, unlike the national monitoring systems in place for hurricanes and wildfires [10]. The lack of national program performance monitoring and management systems makes it challenging to measure the outcome of weather modification activities and coordinate funding and other resources, leaving proper program governance at odds.

The last but not least consideration is liability. As mentioned previously, cloud seeding could lead to unintended consequences such as flash floods. The key argument related to liability here is whether the unintended action constructs negligence. Negligence, which refers to failure to act with reasonable care and causing harm to others in law, is a common legal basis for plaintiffs to file lawsuits against an action. Establishing causation is important in negligence cases, but it can be difficult in lawsuits. One example is the case of Adams v. State discussed by Brendan Woodruff [54]. In the mid-1950s, Pacific Gas & Electric Company (PG&E) contracted North American Weather Consultants (NAWC) to conduct cloud seeding. However, a large storm hit the area, resulting in thirty-seven deaths in Yuba City, California. Survivors in the city sued PG&E and NAWC for their negligence in maintaining and operating their silver iodide generators. The defendants claimed that they stopped seeding before the weather became worse, and thus, they could not have caused the flood. The court found that the plaintiffs failed to establish causation and ruled in favor of the defendants. Again, the legal liability argued in this case highlights the importance of risk management and accountability in weather modification program governance.

Overall, the above program governance considerations imply the importance of establishing proper and efficient processes for resource planning and decision-making when it comes to weather modification. Such processes are essential for cross-region collaboration. A cross-region collaboration often faces challenges related to regulatory differences and equitable distribution of costs and benefits. One example is cloud seeding in the Colorado River Basin. The Colorado River system provides essential water resources to 35–40 million people [58]. To secure water supplies, states located in the upper Colorado River Basin have the option to conduct cloud seeding. But states have different regulations, which can hinder potential cross-region collaborations. For instance, New Mexico, Colorado, and Wyoming claim sovereign ownership of all atmospheric water within their borders [59]. If it is demonstrated that the waters from cloud seeding benefit non-residents downstream, it can lead to litigation and delayed program operations [59]. Another potential challenge for the cross-region collaboration is equitable distribution of costs and benefits for states in the upper and lower basins. For example, a legislator in Wyoming objected to adding funds to the state’s cloud seeding program on the grounds that some induced water went downstream and Wyoming did not receive any credit for that [60].

Cross-region collaborations in weather modification activities also bring up the issue of program oversight, which is essential for program sustainability. As discussed earlier, federal oversight and support of weather modification is negligible beyond basic federal reporting requirements (managed by NOAA; see Figure 1), lacking substantive guidance. All recent attempts to pass a comprehensive federal policy on weather modification programs have failed. Given that, government oversight of weather modification programs mainly comes down to the state level, which focuses on project registration, permitting, professional licensing, and liability (e.g., insurance to mitigate risks) [57]. Recent research has argued that the state-level oversight and regulation tend to be inadequate as well, especially when operations cross state lines [61]. At the local level, there is no program oversight in the sense of rules and regulations. However, public perception and stakeholder engagement becomes critical at the local level. They can provide indirect project oversight via voluntary activities (e.g., donations and program support via other local conservation initiatives). The next section explores these mechanisms by looking into local implementation challenges.

6. Local Implementation

To understand the local implementation challenges faced by weather modification programs, first, it is important to realize the regional variations in weather pattern and landscape and the heterogeneities in local policy and public perception. Due to these variations and heterogeneities, conducting weather modification projects faces different cost–benefit comparisons and governance challenges. In general, a weather modification program is more likely to emerge as a bottom-up initiative by stakeholders (e.g., farmers, ranchers, and small businesses). For instance, shared interests in drought management are a common motivation for such initiatives. The success of a weather modification initiative and its program sustainability often rely on four critical aspects: funding, planning and project management, public acceptance, and outcome measurability, which are also where challenges follow. In this section, we draw from weather modification project experiences in the New Mexico Eastern High Plains (part of the Southern High Plains in the US) and explore these four aspects to shed light on local implementation challenges.

The first challenge of a weather modification project is always funding. The earliest weather modification initiative in the New Mexico Eastern High Plains started in the 1990s. It was funded by a one-time state legislative appropriation, supplemented by donations from local landowners (based on personal communications with Roosevelt Soil & Water Conservation District (RSWCD) board members). Over the time, the program has successfully secured additional state one-time funds and continuous local donations from landowners. A mill levy on local property taxes was attempted but was unsuccessful. Such a funding situation is common among weather modification programs across the US West and Southwest. State and local financial support is crucial to program operations. In the case of New Mexico, a state agency called the Interstate Stream Commission exercises the administrative approval and licensing for state-wide weather modification projects (e.g., see [62]), usually on the grounds of precipitation enhancement and drought management. Although the state’s eastern region accepts weather modification projects due to the rainfall benefits, other parts of the state, especially the mountainous northern counties, often show strong opposition to the program and have pushed for more robust regulations of weather modification activities [63].

When it comes to planning and project management, resource pooling and stakeholder engagement are essential. In the case of New Mexico Eastern High Plains, RSWCD leads in resource planning and project management; the Interstate Stream Commission conducts review and approval of operations; the New Mexico Department of Agriculture provides program oversight; MoUs and agreements among different Soil and Water Conservation Districts help engage stakeholders in the broader region and pool potential financial resources. Among all parties, RSWCD’s leadership is critical in annual program planning and securing state-level legislative support. In terms of project management, the actual cloud seeding operations during the approved period (typically part of the growing season) are contracted to private companies in the region, with the contract covering necessary customized weather reports and other data services. This is a reasonable arrangement given that RSWCD is a non-profit organization and has little asset management capacity (e.g., maintaining a fleet of airplanes).

Even with proper licensing from the state and dedicated project planning and management, conducting cloud seeding in an area of thousands of square miles requires public acceptance. In practice, the necessary public acceptance means majority acceptance. Still, public critiques are common and are usually based on “messes with God’s plan” and conspiracy theories. As Koren argues, the outcomes and consequences of weather modification activities may have become less predictable as the Earth’s climate systems become more volatile [64]. A potential counterargument would be that technological advancements, especially AI-driven data services, could help improve project outcome predictability. It implies the importance of outcome measurability in gaining public acceptance and engaging stakeholders broadly.

In a typical precipitation enhancement application, weather modification project outcome measurability involves at least two aspects. One aspect is the level of beneficial precipitation, regardless of project purposes (recreational or agricultural drought management). It is the desired outcome and can be measured by site-specific precipitation data (e.g., via the CoCoRaHS network; https://www.cocorahs.org/). The other aspect is to measure the level of undesired outcomes, such as unintended flooding. When it comes to outcome measurability, this second aspect often requires additional analytical capacity, including risk assessment, establishing causality, and precise operational control (e.g., being able to abort a cloud seeding operation near real time). In practice, all tasks related to outcome measurability are often contracted to professional meteorologists and weather modification services. Additionally, many state applications for weather modification licenses require operators to have established professional knowledge and experience in relevant areas, which highlights the importance of collaborating with professional service providers in meteorology and cloud seeding. It is exactly what RSWCD does in Eastern New Mexico. A recent New Mexico state legislative bill (New Mexico Legislature 2024 Regular Session; HB 130) related to weather modification programs that passed the House of Representatives clearly emphasizes the importance of scientific efforts and evidence-based methods in measuring benefits and addressing potential environmental risks (e.g., monitoring the level of residuals from cloud seeding materials in the precipitation; see https://www.nmlegis.gov/Sessions/24%20Regular/bills/house/HB0130.pdf, accessed on 10 July 2025).

Another precipitation outcome-related local implementation challenge is the public perception of downwind effects. The early literature suggested that cloud seeding operations can be associated with a significant loss of rain (e.g., 40–45%) in the downwind direction ranging from 100 km to 290 km [65,66]. However, more recent studies showed that the extra-area (downwind) effects are mixed. For instance, both field assessments and simulation modeling suggest that the downwind areas are more likely to receive augmented precipitation, which contradicts the conventional idea of cloud seeding causing potential droughts in neighboring regions (e.g., see [67,68]). Both the previous and new research reinforces the need for regional collaboration (e.g., basin-wide) in weather modification programs and operations. It allows for effective internalization of cost and benefit-related externalities, enabling equitable mechanisms for sharing program costs and benefits.

7. Environmental and Health Concerns

Admittedly, many discussions and arguments about weather modification programs center around their potential environmental impacts and the associated public health risks. And it can even become the core of a public policy debate (e.g., see [69]). At the technical level, concerns are often around the use of silver iodide and the amounts left in the environment. Silver iodide falls onto the earth along with precipitation and increases its concentration in soil and water. For example, Ćurić and Janc found that the concentration of silver iodide could reach 0.14 $\mathsf{\mu }\mathrm{g}/\mathrm{L}$ in a cloud seeding project area in Serbia after 40 years [70]. It is worth noting that the project area used the ground-launching method instead of aircraft-based seeding, which is less accurate in terms of operation controls and could lead to overuse of the seeding materials. And, the relatively high concentration is a cumulative outcome after four decades. More specifically, the iodine in silver iodide compounds poses no environmental risks. It is the potential silver ion (soluble in water; a very toxic heavy metal ion) that can cause significant environmental impacts [71]. However, macroscopic crystals of silver iodide do not dissolve in water [72]. In terms of a safe level of concentration of silver ion in the water, the classic literature suggests a maximum concentration of 50 $\mathsf{\mu }\mathrm{g}/\mathrm{L}$ of silver in drinking water in the US [71]. Recent studies suggest a more conservative toxicity threshold of around 1 $\mathsf{\mu }\mathrm{g}/\mathrm{L}$ [73]. Rainfall silver ion concentrations after cloud seeding operations are significantly lower than these limits. Additionally, there expect to be spatial heterogeneities in setting such threshold limit values (TLV) because of variations in the environmental conditions. For instance, certain plants (e.g., higher plants and fungi) may be more vulnerable to silver accumulation [73].

Recent field assessments tend to suggest that ameliorating factors in the environment can significantly reduce the ecotoxicological impact of silver ion from cloud seeding (e.g., [74]). Other recent studies have shown that ground-based cloud seeding is more significantly associated with silver enrichment in the environment, which is consistent with previous studies. For example, Fisher showed that silver enrichments are almost eight times higher in cases involving ground generators seeding compared to aircraft-only seeding operations using data from Idaho in the US [75]. A study from South Korea showed that the seasonality of cloud seeding operations matters in terms of environmental impacts and winter operations tend to have more impacts [76]. Additionally, rapid chemical analyses of precipitation samples have been developed to allow monitoring of ionic and heavy metal components within a few hours of a seeding operation [77], which makes it more effective in operations management and avoiding overuse of seeding materials. Generally speaking, the potential environmental risks posed by silver iodide through cloud seeding are low unless it reaches an extremely high level of concentration, which would warrant further scientific research to assess its potential impacts. Such further research is critical given that many new local policy developments restricting scientific research and operations of weather modifications have emerged across the US in recent years (see Section 1).

When it comes to project planning and risk management, program managers and project operators should pay attention to potential environmental changes in areas with frequent applications of cloud seeding. As discussed before, continued use of cloud seeding materials in the same geographical areas could affect biota living in both terrestrial and aquatic ecosystems [50]. Given that many regions of the US West and Southwest are experiencing a drier climate and more persistent droughts, the changing environmental conditions will encourage more weather modification programs and more frequent use of silver iodide-based cloud seeding [2]. More contingent rules in monitoring their environmental impacts will become increasingly necessary. Related strategies may include establishing standards for acceptable silver ion concentrations in local soil and water and mandating relevant data reporting during the project application and licensing stage. It could help prevent the accumulation of excessive silver ions in the environment and reduce potential environmental and public health risks. When establishing such regulations, public comments should play a role as diverse populations may exhibit different levels of risk tolerance and public health vulnerability (e.g., urban vs. rural communities). Experimenting and developing alternative seeding agent materials is another potential direction for managing environmental and health impacts of cloud seeding operations (e.g., [78,79]). This new direction of research aligns with operational practices observed in the field, for example, the use of hygroscopic salts (sodium chloride, calcium chloride) in cloud seeding [76,77,80].

8. Concluding Remarks

This paper provides a comprehensive and critical review of weather modification program costs, benefits, and governance, aiming to shed light on the growing interest in adopting weather modification as a local climate management strategy in the US. To deepen our understanding of the widely concerned issues, such as financial burden on taxpayers and environmental risks, the paper also explored the local implementation challenges and common environmental and public health concerns related to weather modification activities. A general observation is that as the changing climate brings more persistent droughts and other extreme weather events to the US West and Southwest, more and more locally (and some regionally) organized weather modification programs have emerged. The new trend comes with at least two challenges. First, due to the lack of federal support, especially regarding research and development support and financial resources, state-level support and other local resources become crucial for sustaining these programs. Additionally, the significant cross-state variations in policymaking will have heterogeneous impacts on new and existing programs. Second, how to address the potential environmental and public health concerns becomes even more important for gaining public support and stakeholder participation. For instance, landowner donations are a critical financial resource for many locally organized weather modification programs. Strong public acceptance and stakeholder participation are indispensable for program sustainability, which are also an important form of social capital [81].

This review is holistic in the sense that it integrates scientific research, policy debate, and community practice to shed light on strategies to adopt weather modification as a local climate management strategy. It is evident that technological advancement, program outreach, and research on managing environmental impacts are essential in developing and sustaining local or region-wide weather modification programs.

Technological advancement can help address project operating efficiency issues by supporting project planning with better data intelligence and exercising more precise control over cloud seeding activities. Specifically, high precision seeding can reduce overuse of cloud seeding materials and hence further reduce silver ion concentrations left in soil and water. Better data intelligence can enable near-real-time forecasts of local weather conditions and cloud dynamics during the seeding operation. First, it can help optimize operating costs (see the note callouts in Figure 3) while reaching desired seeding outcomes. Second, it can help reduce unintended consequences such as flash flooding by aborting the seeding operation when excessive precipitation is forecasted. In general, technological advancement in cloud seeding materials and operations can also enhance knowledge dissemination and program outreach for gaining public support.

Regarding public acceptance and concerns about program impacts, it is important to note that risk perception is a relative measure and exhibits significant heterogeneities across individuals and communities. To help develop effective program outreach strategies, both scientific research on weather modification technologies and social science research on best project implementation strategies are fundamental. Meanwhile, it is equally important for stakeholders to assess environmental risks related to weather modification activities in a comparative sense or framework. For example, a comparison of environmental risks related to fertilizer use and those related to weather modification may help alleviate unnecessary misunderstanding of the use of a particular seeding material. In that sense, evidence-based risk assessment is important [82].

Lastly, this review is limited in its scope as it focuses on program experiences and application scenarios in the US. However, our literature review and discussion point to at least four directions of future research: (1) the potential of integrating ground-based approach and UAS-based approach in the future to improve seeding effectiveness and better manage operation costs and environmental impacts; (2) developing in-depth case studies with focus on a specific region or watershed, and this is where cross-disciplinary collaboration involving expertise in climatology, hydrology, environmental sciences, and system engineering can fructify; (3) providing more and updated scientific evidence on the environmental impacts of cloud seeding materials, especially regarding silver ion accumulation and alternative seeding materials; and (4) public acceptance and concerns about weather modification, which can vary significantly across different countries and cultures. Future research should investigate international program experiences, including a comparison of the US program experience and international program experiences, to shed light on best practices.