Xubin Zeng Featured in AMS Headlines: Science Spotlight -- The Global Precipitation Experiment: A New Decade-Long Advanced Multiscale Research Opportunity
by Xubin Zeng et al.
A rare snowfall on saguaro cactus taken in Xubin Zeng's backyard, Tucson, Arizona, in early March 2023
Image: Xubin Zeng
Congratulations to HAS Professor Xubin Zeng and collaborators Annalisa Cherchi, National Research Council of Italy, and Chris Lennard, University of Cape Town, South Africa, whose research efforts were recently recognized by the American Meteorological Society in their Headlines--Science Spotlight news section: The Global Precipitation Experiment: A New Decade-Long Advanced Multiscale Research Opportunity.
| → Key Messages From Global Precipitation Experiment—A New World Climate Research Programme Lighthouse Activity |
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Precipitation is a critical component of the water cycle and a major driver of atmospheric circulation through the latent heating associated with condensation and evaporation. Many high-impact weather events affecting society are manifested as too much or too little precipitation. For these reasons, precipitation has already received much attention from numerous national and international projects. Nevertheless, the accurate measurements, modeling, and prediction of precipitation remain one of the fundamental challenges in weather, water, and climate research.
As precipitation is produced by complex moist processes and their multiscale interactions with atmospheric dynamics and other components of the Earth system, the strategy of the Global Precipitation Experiment (GPEX) is to make sustained progress with this challenge through observations, understanding, modeling, and capacity development, which will lead to a quiet yet progressive revolution, just like the case for numerical weather prediction.
GPEX was first discussed in 2020 among various U.S. agencies to address the slow progress in improving precipitation prediction. This effort was elevated in 2021 to an international initiative to be pursued through the World Climate Research Programme (WCRP). A GPEX Tiger Team prepared a white paper on the GPEX strategy in 2022. This team was expanded in 2023 to form a GPEX Science Team in developing the Science Plan, with the launch of GPEX as a new WCRP Lighthouse Activity in October 2023. This team was then transitioned to the interim Scientific Steering Committee in 2024, with the new membership in 2025 tasked with implementing the GPEX Science Plan.
GPEX will address four main science questions related to
- Reducing precipitation product uncertainties
- Improving understanding of precipitation and related processes
- Improving precipitation prediction and projection
- Enhancing regional and local capacity
Its four key activities organized into four working groups will cover four storm systems:
- Atmospheric rivers
- Mesoscale convective systems
- Monsoons
- Tropical cyclones
Field campaigns are needed to better understand precipitation processes. Indeed, the 1974 field campaign (GATE) data over the tropical Atlantic are still widely used for process understanding.
What is most exciting about GPEX is the planning of its unprecedented, globally coordinated atmosphere–land–ocean coupled field campaigns with in situ, airborne, and satellite measurements. A key activity is to identify and approve potential anchor projects for each storm system, and to develop international partnerships for coordinated field campaigns around these anchor projects.
GPEX will develop gridded precipitation-relevant datasets with high temporal and spatial resolutions that will complement existing efforts. Such datasets already exist, but they differ from each other (e.g., for extreme precipitation and for how precipitation relates to other variables). GPEX will also pursue a baseline surface precipitation network, similar to the long-term radiation and atmospheric aerosol networks. This network will ensure high-quality measurements of precipitation rate, type, and hydrometeor size distribution, which can also be used to calibrate other measurements, improving the overall quality of global precipitation datasets.
GPEX will seek to coordinate precipitation analyses and forecasts from major prediction centers for the GPEX period and support the establishment of multimodel databases, along with common evaluation metrics for deterministic, probabilistic, and extreme forecasts of precipitation. While kilometer-scale modeling offers a very useful tool for precipitation simulation and prediction, significant biases persist, because physical processes—such as shallow convection, turbulence, and cloud microphysics—still need to be parameterized. Therefore, GPEX will focus on model simulations at various resolutions and address questions such as: How can process understanding from kilometer-scale modeling help improve coarser-resolution modeling? Furthermore, GPEX will emphasize the cross-scale process understanding of land–atmosphere and land–hydrology interactions and their implementation in climate models.
As WCRP has already set up projects on capacity development, GPEX will focus on entraining scientists and graduate students into global field campaigns. Local researchers understand regional and local processes and will contribute to model evaluation, development, and experiment design for these regions.
GPEX will move forward with three phases:
- 2–3 years to plan field campaigns and carry out other activities
- 2–4 years to organize and conduct field campaigns and carry out all activities and
- 2–3 years to pursue postcampaign activities
The GPEX implementation strategy is to lead few activities, but do them well, with strong partnership. GPEX activity will be completed in a decade or so and then be fully integrated into WCRP Core Projects.
Through our BAMS article, we invite the broader community to contribute to GPEX as we seek to engage in an unprecedented global effort to advance understanding of the hydroclimate, and the modeling and measurement of precipitation.
If you are excited about GPEX, please get involved!
More About the Collaborators & What's Next
Xubin Zeng enjoying a tour of Budapest in April 2024 after the GEWEX Scientific Steering Group Meeting there.
“While precipitation is the driver of the water cycle, river flow measurements provide an excellent constraint for each river basin.”
“My initial interest was in physics, and my PhD research on chaos theory and its applications to the atmosphere was advised by an atmospheric scientist and a theoretical physicist. After learning about atmospheric physics in college, such as clouds, precipitation, radiation, and turbulence, I saw the relevance of these topics to our daily life and wanted to better understand weather, water, and climate. Decades later, I am now connecting with physicists again in an attempt to link quantum science and computing to our field. Life is a spiral!” — Xubin Zeng, The University of Arizona
“My first interest was in physics, but my degree course in the late 1990s was also offering geophysics classes, and I started to be interested in them. Among the classes was a short course on meteorology and climatology that showed me fascinating aspects of this science, and from there I started with a degree thesis and later on with a PhD. While preparing my degree thesis, I read a poem on how people living in monsoon countries see and wait for precipitation. It was quite a different perspective from mine living in Italy, far from the tropics. Nowadays, perspectives have changed for all of us, and how we wait for precipitation and/or are scared by its scarcity or extreme abundance are becoming common because of climate change and its consequences.” —Annalisa Cherchi, National Research Council of Italy
Chris Lennard doing what he enjoys the most—running on Table Mountain in Cape Town, South Africa, in the pouring rain.
“I grew up on the South African highveld. During the summer, I would be mesmerized by the growth of a small cumulus cloud as it bubbled up into a towering cumulonimbus full of lightning, thunder, heavy rain droplets, hail, and raw power. Gazing out of my window, I hoped we would get lucky and it would pass overhead and drench us with rain, and we would feel the CLAP of lightning-triggered thunder. If we were unlucky, there would be golf ball– or tennis ball–size hail! My mother would always shout at me to get away from the window, which I never did. At university I studied atmosphere and ocean science so I could understand these phenomena better, and now I want to understand how climate change will impact events like these in my continent as we approach 1.5 and 2 degrees Celsius of global warming.” — Chris Lennard, University of Cape Town
BAMS asked the collaborators the following questions. You can find their Q&A here (scroll down to the Metadata section).
- What would you like readers to learn from this article?
- How did you become interested in the topic of this article?
- What surprised you most about the work you document in this article?
- What was the biggest challenge you encountered while doing this work? And finally...
- What's next for each of the collaborators?
Xubin Zeng having fun and thinking about the glacier mass balance from snowfall, sublimation, melt, and glacier flow during a visit to a low-altitude modern glacier around 2,900 meters above sea level just 130 miles (210 km) away from his hometown in Sichuan Province, China.
Image: Xubin Zeng
"What’s next is to implement the GPEX Science Plan! The organizational structure is in place, with the GPEX Scientific Steering Committee cochairs, the cochairs of its four working groups, and most of the members already appointed. The great challenge would be the financial support of the field campaigns; precipitation-related dataset development; process understanding, modeling, and prediction; and capacity development at this chaotic time of our life in the world.”
—Xubin Zeng, The University of Arizona