By Karl Blankenship, Bayjournal.com
Trend toward more and heavier rainfall and warmer weather in region threaten to overwhelm current actions
This year’s persistent high river flows into the Bay prompted many of those working on Chesapeake issues to ask the question: “Is this the new normal?”
The good news is that this year’s extreme precipitation is not likely to become “normal” anytime soon. But it does highlight an inconvenient truth: When it comes to the weather, the future won’t be like the past.
It most likely will continue a trend that’s been going on for decades: wetter weather in general and heavier rain in extreme storms.
That has ramifications for meeting Bay nutrient reduction goals. When it comes to runoff, “flow is fate,” said Lewis Linker, modeling coordinator with the state-federal Bay Program partnership. More rain moves more nitrogen off the landscape and into the Bay, while heavier storms dislodge sediment particles — and the phosphorus that binds to them — and moves them downstream as well.
When they reach the Bay, nitrogen and phosphorus contribute to cloudy water, algae blooms and oxygen-starved “dead zones.”
The Bay Program is taking its first steps toward addressing how Chesapeake-related cleanup actions will adapt to climate change, which is critical as some runoff control actions implemented now may be in place for decades.
States have until April to provide the U.S. Environmental Protection Agency with written descriptions of how they will address climate as part of their updated Bay cleanup plans. In 2021, they will be required to adopt additional measurable nutrient reduction goals needed to offset the impact of climate changes expected through the 2025 cleanup deadline.
For the Bay, climate change isn’t a future concern. Monitoring shows rainfall in the watershed has increased about 10 percent over the last century, though the changes have differed from place to place with precipitation in the northern part of the watershed increasing faster than in the southern portion.
There’s also been an increase in the number of severe storms. The National Climate Assessment released by the federal government in October said the amount of precipitation during heavy rainfall events has increased by about 50 percent since 1958 in the nation’s Northeast region, which includes most of the Bay watershed.
But the computer models the Bay Program used to estimate the necessary nutrient reductions were based on precipitation observed in the 1990s, and did not account for the gradual rainfall increase when Bay nutrient reduction goals were set in 2010. Based on past trends, average precipitation from the 1990s to 2025 would be expected to increase by a bit more than 3 percent.
With that factored in, the models now show that further nutrient reductions would be needed to offset the increased flows — 9.1 million more pounds of nitrogen and 490,000 more pounds of phosphorus. That would be a 19 percent nitrogen reduction, and a 73 percent phosphorus reduction beyond what the region already needs to accomplish between now and 2025.
Those figures represent an “initial estimate,” Linker cautioned, and may be refined in the coming year based on new information.
Further complicating cleanup efforts, the changing climate conditions will also hamper the effectiveness of practices commonly used to manage runoff. Manure storage facilities on farms and stormwater detention ponds in cities — all designed to manage “typical” rainfall events of the past — will increasingly be overwhelmed as rainfall increases, especially as more arrives in storms.
“I’ve been hearing from some of the conservation districts that we’re seeing erosion in areas where we never previously saw it,” said Mark Dubin, agricultural technical adviser with the Bay Program. “That’s an indicator that the rainfall we’re getting is challenging our previous standards for, and designs for, conservation practices, whether it be tillage or crop residue management or water control structures.”
Investments being made today in things like costly stormwater control systems need to anticipate the impacts of more severe storms in the future.
“We have a lot of investment in stormwater management that is designed for a particular capacity and inflow amount,” Linker said. “And as the inflow amount is increasing, we need to essentially protect our investment.”
Mark Bennett, director to the U.S. Geological Survey’s West Virginia and Virginia Water Science Center and co-chair of the Bay Program’s Climate Resiliency Workgroup, cautioned that it will be a daunting task to re-examine the effectiveness of the dozens of best management practices implemented in the region to meet Bay goals under future climate scenarios.
Not only will increased rainfall compromise the effectiveness of some control measures, but changes in temperatures and growing seasons could also reduce the effectiveness of buffers, cover crops and other practices that rely on vegetation. In some cases, the types of plants or trees being used may need to be changed to get optimal results under future conditions.
In their updated cleanup plans, states are supposed to explain how they will plan for the future, as well as how they can promote nutrient control practices that offer dual benefits by helping to address problems caused by climate change. For instance, streamside forest buffers that help reduce runoff can also help control flooding during heavy rains.
David Flores, a policy analyst with the nonprofit Center for Progressive Reform who has been tracking the Bay Program’s efforts to incorporate climate change, acknowledged that the science is too incomplete in many cases to know how specific control practices should be modified to adjust to climate change. But, he said, he would like the upcoming state plans to make firm commitments to help fill that knowledge gap.
For instance, he said, states could pledge to evaluate and monitor how different stormwater and other runoff control practices are performing during storms and to commit to incorporate that information into new design standards.
“The plans should really lay out, in detail, certain things that set up some accountability,” Flores said.
Other ways the plans could factor in climate change, he said, would be to avoid putting runoff control practices in places likely to be inundated by sea level rise in the next few decades, and to prioritize those that would also help mitigate damage in flood-prone areas.
“I am optimistic in that I think that there will be jurisdictions that step up and adopt a serious scope of work to address climate as part of their respective implementation plans,” Flores said.
One already has. The District of Columbia has agreed to go beyond the written explanations required in new cleanup plans and is adopting numeric nutrient reduction goals for 2025 — three years earlier than required. That means an 6,000 additional pounds of nitrogen and an additional 1,000 pounds phosphorus reductions by 2025.
The district has already exceeded its existing 2025 goals, in large part because of better-than-expected performance by the Blue Plains Regional Advanced Wastewater Treatment Plant. But it has committed to not count the Blue Plains overachievement toward its additional climate reduction goals. Instead, it will achieve them by putting more actions on the ground, said Katherine Antos, chief of the Partnering and Environmental Conservation Branch of the district’s Department of Energy & Environment.
She said the district will target additional efforts, largely through incentive programs, in watersheds that have their own local water quality problems and in areas that are more vulnerable to climate impacts — such as flood risks or urban heat island impacts.
That means promoting actions that provide multiple benefits, like increasing tree canopy cover, increasing stormwater retention and doing more stream restoration in those areas.
“These are not only going to improve our local waters and the Chesapeake Bay, but they’re also going to help us be more resilient to those changing weather conditions,” Antos said.
The district is also revisiting whether stormwater design standards are adequate to handle more frequent or more intense rainfall events in the future.
“It’s only going to become more difficult to achieve water quality standards in the Bay over time,” Antos said.
Not only will more precipitation and severe storms drive more nutrients into the Bay, she noted, but rising sea levels will drown tidal wetlands at an increasing rate, eliminating their ability to absorb nutrients and mitigate some of the impacts.
“That means that much more nitrogen and phosphorus is going to need to be reduced from the watershed. We need to start planning for that now, because what we need to do by 2025 is small compared to the impacts by 2050 or 2080, so let’s start putting ourselves on the right path now,” Antos said.
“And while the district is doing our part,” she added, “we’re only going to be successful as a watershed if the partnership does its part.”