At the first virtual International Rain Enhancement Forum (IREF), researchers from Khalifa University shared their innovative methodologies and new insights to enhancing rainfall across the UAE.
The International Rain Enhancement Forum (IREF) is a global platform that brings together leading international and national experts, researchers, scientists, and stakeholders to tackle pressing water and sustainability issues worldwide.
In the 2021 forum, three Khalifa University researchers shared presentations on their innovative research and advancements in materials and methods applicable to rain enhancement. After the presentations, the researchers were joined by Dr. Steve Griffiths, Senior Vice President of Research and Development at KU, to further discuss their work in a panel discussion.
Topics included the application of nanotechnology for developing novel cloud seeding materials, the study of the effects of electrical charges on cloud droplet formation, algorithms for determining suitable cloud seeding conditions, and the integration of multiple modeling efforts and novel data to create a unified weather forecasting model.
Porous Nanoparticles for Cold Cloud Seeding
Dr. Linda Zou, Professor of Civil Infrastructure and Environmental Engineering, introduced porous nanoparticles and their potential for cold cloud seeding. Cloud seeding is the process where substances are put into clouds to stimulate the formation of rain drops. Natural cold cloud rainfall occurs when ice crystals from clouds high in the atmosphere fall into clouds lower down. The ice crystals act like seeds to start the formation of larger crystals which leads to raindrop formation.
Dr. Zou uses nanotechnology to create materials called ice nucleating particles (INPs), which act in the same way as natural ice crystals, forming supercooled water droplets at temperatures lower than -38° Celsius. Cold cloud seeding works in the area of warm surface temperature, allowing ice nucleation at temperatures around -8° Celsius, making cloud seeding relatively easier.
But cloud seeding isn’t just used for enhancing precipitation; it can also be used to evaporate fog and clouds. If the fog is very cold, adding large quantities of INPs causes the fog to dissipate as all the liquid turns to ice—a useful technique in areas that see a lot of winter fog, such as the UAE. However, for this to work, the fog needs to be very cold, and desert temperatures rarely drop to the required temperature. This is where cloud seeding techniques can be used. Cloud seeding can also suppress the formation of hail as the artificial and natural ice particles compete with each other for the available liquid water, with seeding accelerating the development of raindrops, transforming the clouds from dangerous to benign.
Dr. Zou applies nanotechnology to conventional cloud seeding materials, engineering particles with optimal properties to ensure the maximum amount of ice nucleation. Reduced graphene oxide serves as the template for ice crystal growth due to a similar hexagonal lattice structure while the addition of silicon oxide nanoparticles enhances the overall water molecule adsorption capabilities of the composite particle.
The silicon oxide nanoparticles create pores in the final product and play an essential role in ice nucleation as liquid water collects in the pores. Dr. Zou’s experiments showed that the particles caused ice nucleation in temperatures of around -8° Celsius, with these results indicating how cold cloud seeding can be used in actual operations, including hailstorm suppression and fog reduction.
Accurately Modeling the Weather
Following this presentation on rainfall generation using porous nanoparticles, Dr. Diana Francis, Senior Scientist and Environmental and Geophysical Sciences (ENGEOS) Lab Head, covered her lab’s efforts to develop a unified multi-component atmospheric model for rain enhancement applications in the UAE. While the UAE is known for being hot and dry, rain does fall during the winter months. However, perhaps surprisingly, the UAE also possesses unique weather systems that can develop during the summer months, occasionally providing water to rain-starved areas and relief from the excessive heat. These systems are known as mesoscale convective systems (MCS) and Dr. Francis wants to be able to predict them.
Numerical models are a powerful tool to improve our understanding of the processes in the atmosphere and help predict weather patterns and their impact. Dr. Francis’ team has been assessing and validating the components of their unified model with two investigations on dust and climate and summertime rainfall.
An MCS is a cluster of storms that moves as a single system and for one to develop in a hyper arid environment like the UAE, a combination of factors ranging from local to regional scale is needed, including a steep temperature gradient on the ground between the land and the surrounding seas. If cold air from the sea meets hot air from the desert, there is potential for an MCS to form. Dr. Francis found that MCS formation and its impacts on the atmospheric state are not accounted for in many simulations of weather over the UAE, notably underestimating the observed cloud cover. This has important implications for the use of the current state-of-the-art models for climate projects in arid regions. It is therefore important to develop comprehensive numerical models and assess their capability in accurately representing the regional environment.
Dust emissions from the Arabian Peninsula also play a critical role in the weather over the UAE. Dust cover induces a significant net warming effect at the surface and in the atmosphere during the night, modifying the atmosphere at lower levels. Dr. Francis explained that dust needs to be considered when predicting, designing, and conducting cloud-seeding operations in the UAE because of the impact on circulation and the development of clouds. The role dust plays in the climate system of the Arabian Peninsula needs to be considered in weather forecast systems to achieve improved accuracy.
As desert regions are expected to expand in the future and are sensitive to climate change, regional models need to be further developed to better represent the UAE environment and the atmospheric processes and interactions. Discrepancies in any model may result in inefficient cloud-seeding operations, highlighting the need for accurate models and forecasting systems, particularly as summertime clouds offer the best chances for cloud seeding.
Convection over the UAE and Implications for Cloud Seeding Operations
Part of developing an effective model is understanding the processes involved. Postdoctoral Fellow Dr. Ricardo Fonseca detailed how convection over the UAE happens and its implications for cloud-seeding operations. The vast majority of precipitation occurs between December and March but rainfall at isolated spots in the summer season is not uncommon, with accurate model forecasts crucial for any intended cloud seeding operations to take advantage of this cloud formation. Dr. Fonseca explained that two atmospheric features play an important role in triggering summertime convection in the UAE: The Arabian Heat Low (AHL) and Intertropical Discontinuity (ITD). The AHL is a weather system that develops inland as a result of strong surface heating by the sun while the ITD is the boundary between the hot and dry winds from the desert and the cooler and moister winds from the Arabian Sea. Using a rainfall event that occurred in 2017 over the Al Hajar mountains to the east of the UAE, Dr. Fonseca used various models to simulate the event. The results indicate that, of the models tested, the Weather Research and Forecasting (WRF) Model does a reasonable job of simulating the convective event over the Al Hajar mountains in September 2017, despite certain deficiencies in the model. Dr. Fonseca suggests that WRF predictions can be used for guidance into cloud seeding activities in the UAE and any modeling work needs to consider the important circulation features in the atmosphere over the Arabian Peninsula in the summer.
The KU panelists emphasized the important role research into rain enhancement innovations, including cloud seeding technologies and accurate weather modeling systems, will have on the UAE’s future water and food security goals, and revealed the critical work underway at Khalifa University aimed at turning this research into practical applications.
17 February 2021