Emergent patterns in nature and society

Posts tagged “cascading effects

One third of Earth’s largest groundwater basins are being rapidly depleted by human consumption

NASA and CalTech report two studies that quantify the depletion rate of major aquifers in the planet. Here are the links to the papers, both open access:

  1. Quantifying renewable groundwater stress with GRACE
  2. Uncertainty in global groundwater storage estimates in a Total Groundwater Stress framework

This means that significant segments of Earth’s population are consuming groundwater quickly without knowing when it might run out, the researchers conclude […]

The studies are the first to comprehensively characterize global groundwater losses with data from space, using readings generated by NASA’s twin GRACE satellites. GRACE measures dips and bumps in Earth’s gravity, which are affected by the mass of water. In the first paper, researchers found that 13 of the planet’s 37 largest aquifers studied between 2003 and 2013 were being depleted while receiving little to no recharge.

Eight were classified as “overstressed,” with nearly no natural replenishment to offset usage. Another five were found to be “extremely” or “highly” stressed, depending upon the level of replenishment in each. Those aquifers were still being depleted but had some water flowing back into them.

The most overburdened aquifers are in the world’s driest areas, where populations draw heavily on underground water. Climate change and population growth are expected to intensify the problem.

“What happens when a highly stressed aquifer is located in a region with socioeconomic or political tensions that can’t supplement declining water supplies fast enough?” asked Alexandra Richey, the lead author on both studies, who conducted the research as a UCI doctoral student. “We’re trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods.”

The research team — which included co-authors from NASA, the National Center for Atmospheric Research, National Taiwan University and UC Santa Barbara — found that the Arabian Aquifer System, an important water source for more than 60 million people, is the most overstressed in the world.

The Indus Basin aquifer of northwestern India and Pakistan is the second-most overstressed, and the Murzuk-Djado Basin in northern Africa is third. […]

In a companion paper published today in the same journal, the scientists conclude that the total remaining volume of the world’s usable groundwater is poorly known, with estimates that often vary widely. The total groundwater volume is likely far less than rudimentary estimates made decades ago. By comparing their satellite-derived groundwater loss rates to what little data exist on groundwater availability, the researchers found major discrepancies in projected “time to depletion.” In the overstressed Northwest Sahara Aquifer System, for example, time to depletion estimates varied between 10 years and 21,000 years.

“We don’t actually know how much is stored in each of these aquifers. Estimates of remaining storage might vary from decades to millennia,” said Richey. “In a water-scarce society, we can no longer tolerate this level of uncertainty, especially since groundwater is disappearing so rapidly.”

The study notes that the dearth of groundwater is already leading to significant ecological damage, including depleted rivers, declining water quality and subsiding land.

Both papers draw the attention to yet another driver of ecological regime shifts that might be occurring unnoticed by the challenges of data gathering. The recharging of aquifers could be thought of as a regime shift where the dominant feedbacks relate to the recharging rate but also through the coupling of vegetation and rain patterns produced by moisturising recycling. Far fetched idea that worth keep an eye on. For the time being, both papers go to the ‘potential regime shifts’ folder.


Cascading effects of permafrost melting

EurekAlert reports today the latest findings of Michael Gooseff presented in the annual meeting of the Ecological Society of America. It’s a suggested reading if you are into the impacts of climate change on polar areas. I’ll only highlight some of the links between drivers of regime shifts that potentially cause cascading effects among them.

The increasing melting of polar ice is driven by climate change. Ice is melting faster and it’s expected to “change flow patterns, expand the stream networks, and change both the location of habitats and timing of life cycles” . For example, Gooseff reports “temperatures and snow and rain across the tundra shifts annually and seasonally. We know that fall is beginning later than it once did”.

One of the most common link reported in the literature is that as polar areas warm up, permafrost begins to melt and liberate huge amounts of carbon dioxide and methane that has been stored for centuries. As carbon is released to the atmosphere, climate change is reinforced by the permafrost melting feedback loop.

However, something I haven’t seen is the link between permafrost melting and nutrients runoff. The latest is an important driver of regime shifts like eutrophication, hypoxia and transitions in food webs. Here are some notes:

Extended frost-free time causes soils that do thaw annually to have longer active periods when microbes can mineralize nutrients. While the soils remain frost free longer, plants continue their normal cycle dictated by the length and intensity of daylight, which has not changed. Microbes may continue to create nutrients, but the plants no longer use them, so that when rain or meltwater comes the nutrients leach into the rivers and streams.

“That is exactly what we are seeing,” said Gooseff. “In September and October, we see a substantial increase in nutrients in the water. Concentrations increase many times for nutrients such as nitrate and ammonium.”

I wonder how such linkages will change the map of dead zones, or areas under hypoxia regime around the world. Do you think it will be strong enough to create new dots in polar coasts?

Dead zones map created by the Earth Observatory NASA

The Dead Zones map was created by EarthObservatory | NASA based on the following paper:

Diaz, R. J., & Rosenberg, R. (2008). Spreading Dead Zones and Consequences for Marine Ecosystems. Science, 321(5891), 926-929.

via: Polar climate change may lead to ecological change. | EurekAlert