Knowing how much precipitation is likely to fall in a region is essential when designing stormwater infrastructure, roadways, and airports. Accurately projecting future rainfall intensity and frequency requires up-to-date assessments of current climate conditions and model-generated data for future horizons.
The National Oceanic and Atmospheric Administration (NOAA) is tapping the expertise of the Illinois State Water Survey (ISWS) to finish a multi-year collaboration updating climate model projections for its Atlas 14, which serves as the benchmark for precipitation frequency values across the United States.
The Water Survey joined the University of Wisconsin-Madison and the Pennsylvania State University to complete the initiative.
Momcilo Markus, a principal research scientist at ISWS and research associate professor in the Natural Resources and Environmental Sciences and the Agricultural and Biological Engineering departments at the University of Illinois, has been at the forefront of the survey’s research using statistical analyses and observational data to detect trends at both the state-level, such as Bulletin 75 in Illinois, and different regions of the United States.
“The purpose of the analysis is the same – to create precipitation frequency standards,” Markus said, “and the observed and projected increases in heavy precipitation happening in the Northeast are comparable to the increasing rainfall trends happening in Illinois, that we documented in Bulletin 75.”
Kevin Grady, a postdoctoral research associate at ISWS, joined the project in March 2019 to evaluate the performance of the individual models used for projecting future precipitation frequencies.
“The ensemble of models we used contained projections not just for the future, but for the past as well, as far back as 1960,” said Grady, “We can compare these model projections alongside actual historical observations to assess how well each model can ‘predict’ the past. Making the reasonable assumption that models that are better at simulating the past will give more accurate forecasts for the future, we can then weigh these better performing models higher when looking at the future.”
The vast computing power required for simulating the weather and climate means today’s models are run using massive supercomputers.
“When we were tasked to model the entire Northeast region, we knew we needed faster computational power,” Markus said. Markus, a two-time faculty fellow at the National Center for Supercomputing Applications (NCSA) contacted Seid Koric, a technical assistant director at NCSA and associate research professor at the U of I’s Department of Mechanical Science and Engineering, to partner together to run climate simulations that would not have been possible without using the Blue Waters supercomputer.
“Supercomputers traditionally play an important role in understanding the far-reaching interactions between hydrology, flora, weather, and climate change. These extremely complex interactions are modeled by sophisticated computer models at time scales ranging from days to centuries. They rely heavily on supercomputing systems built to quickly process the massive datasets used in weather and climate modeling.”
“Inputs into the statistical models developed by Dr. Markus and his collaborators from the University of Wisconsin are the outputs from many climate models from 800 locations across the Northeast for 140 years,” Koric said. “All of these variations quickly add up to the millions of required computational runs, and each run would take roughly 3 hours to complete on a standard desktop; but we were able to use high-throughput computing, where we were sending each of these computational tasks to a different processing unit of Blue Waters. Thus, we ran thousands of these independent tasks simultaneously, completing them all within hours instead of the many months that would take on a desktop.”
This process enabled Markus and the team to experiment with different climate scenarios while tuning the weights of models and choosing the optimal simulations.
“Working together, our team was able even to optimize and improve some model parameters, which will be a very treasured asset for future simulations,” said Koric.
The output from these models will drive forward climate science, helping scientists and legislators understand how the climate is changing across the Northeastern United States.
“The goal of this work is to present a development framework for NOAA precipitation frequency studies to consider future climate scenarios that are computationally efficient and provide an accurate estimation of non-stationary precipitation characteristics,” said Mark Glaudemans, Geo-Intelligence Division Director, Office of Water Prediction, National Weather Service at NOAA.
“These advances will help implement new regulations for development like analyzing waterways and helping inform adequate designs for highways, airports, and urban stormwater drainage infrastructure by producing more accurate rainfall projected frequency estimates for years to come,” Markus said.
Despite the increasing accuracy of the models that point to more frequent heavy rainfall events to come, Markus acknowledges that one of the biggest challenges is for managers to adopt the projected standards now to prepare for the future.
“Our climate models are getting better and better and more accurate every year and every decade, but the statistical analysis of the past data offers much less uncertainty, so natural resource managers hesitate to use projections, because they are more uncertain than observations,” Markus said. “This brings us to the biggest challenge for managers ‘Do I ignore the fact that precipitation will be increasing over 50 years, or do I account for it and how?’”
In many ways, climate modeling is an extension of weather forecasting, but focusing on changes over decades rather than hours.
“Agencies typically adopt present standards when constructing culverts, sewers, etc., but what happens after 50 years when higher rainfall comes? Are these structures going to be resilient?” Markus questioned.
NOAA’s updated methodology for Atlas 14 will be available later this fall.
The Illinois State Water Survey is a division of the Prairie Research Institute at the University of Illinois Urbana-Champaign.
