Stefan

May

2022

H2O – The molecule that made us

Very interesting documentary with impressive pictures around the big problem of dwindling water: “Water is the prerequisite for life. A few tiny drops are already enough to make a withered desert blossom anew. Water also played an important role in the emergence of early civilizations. Control of the resource gave humans clear advantages. But access to clean water is becoming increasingly difficult, and fear for the resource is growing. – A documentary series tracing our relationship with the “blue gold.””

May

2022

Amazonia´s flying rivers – no forest, no water

Interesting and informative documentary: The Amazon rainforest is not only the earth’s green lung (absorbing and storing carbon dioxide from the air and converting it to oxygen) it is also its air conditioner: intact forests suck in rain clouds from the Atlantic and evaporate water. In this way they cool the earth. Without forest, no water: if more and more forest disappears, this phenomenon of ‘flying rivers’ acting like a gigantic water pump can no longer exist. Scientists, politicians and environmental activists explain the fragile balance.

Apr

2022

Land use and climate change : an interview with Millan Millan

Meteorologist Millan Millan’s research work discovered that rain was disappearing because land use was affecting evapotranspiration rates. In this podcast he talks about what we need to do to restore rains and ecosystems.

Apr

2022

Volunteers plant trees for a new Phoenix ‘cool corridor’

Phoenix has committed to establish by 2030 100 “cool corridors” in shade-starved zones with high pedestrian traffic. Without more trees and other urban cooling features, the Phoenix area stands to lose lives collectively valued in the billions of dollars in coming decades, a Nature Conservancy study concluded last year.

Apr

2022

Intense atmospheric rivers can weaken ice shelf stability at the Antarctic Peninsula

Scientists warn the biggest remaining ice shelf in the Antarctic Peninsula is at risk of total collapse due to ‘rivers in the sky’.

We show that the most intense atmospheric rivers induce extremes in temperature, surface melt, sea-ice disintegration, or large swells that destabilize the ice shelves with 40% probability. This was observed during the collapses of the Larsen A and B ice shelves during the summers of 1995 and 2002 respectively. Overall, 60% of calving events from 2000–2020 were triggered by atmospheric rivers.

Apr

2022

Revealing the widespread potential of forests to increase low level cloud cover

Forests, afforestation, evapotranspiration, and its cooling effect:

However, changing the forest cover can further affect the climate system through biophysical effects. One such effect that is seldom studied is how afforestation can alter the cloud regime, which can potentially have repercussions on the hydrological cycle, the surface radiation budget and on planetary albedo itself. Here we provide a global scale assessment of this effect derived from satellite remote sensing observations. We show that for 67% of sampled areas across the world, afforestation would increase low level cloud cover, which should have a cooling effect on the planet. We further reveal a dependency of this effect on forest type, notably in Europe where needleleaf forests generate more clouds than broadleaf forests.

The scientists emphasize that land-based climate mitigation through afforestation, forest restoration and avoided deforestation should not be reasoned purely in terms of carbon capture. Instead, policies should include the wider climate benefits that forests offer, including increasing cloud cover for localized cooling and generating rainfall, giving forests additional hydrological value.

Apr

2022

Drought self-propagation in drylands due to land–atmosphere feedbacks

It has consequences, if (agricultural or forest) soils can hold less and less water and dry out. Although this research is on global drylands, I dare to guess that the same pattern applies to our desiccating agricultural landscapes.

Reduced evaporation due to dry soils can affect the land surface energy balance, with implications for local and downwind precipitation. […] We show that dryland droughts are particularly prone to self-propagating because evaporation tends to respond strongly to enhanced soil water stress. In drylands, precipitation can decline by more than 15% due to upwind drought during a single event and up to 30% during individual months. In light of projected widespread reductions in water availability, this feedback may further exacerbate future droughts.

Description of the figure: »Meteorological drought is frequently triggered by weaker-than-usual dynamical saturation-enabling mechanisms (conceptualized as low precipitation efficiency; Peffʹ < 0), which in turn may respond to a remote forcing, such as anomalous sea surface temperatures. Once that happens, limited precipitation (Pʹ < 0) causes soil desiccation (SMʹ < 0) and soil stress, exacerbated by the high potential evaporation due to clear skies and elevated temperatures. Then, evaporation becomes (more) water limited (E’ < 0). The reduction in near-surface air moistening — extending across the troposphere via vertical mixing—causes a reduction in water vapour being exported downwind (Qʹ < 0). Therefore, further downwind, for the same precipitation efficiency, even less precipitation is expected (Pʹ < 0), contributing to downwind drought onset (SMʹ < 0, Eʹ < 0). Moreover, since water vapour is known to enhance uplift, additional reductions are possible for convective precipitation (Peffʹ, Pʹ, SMʹ, Eʹ « 0).«

Apr

2022

Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation

This is fascinating research, showing the interrelation of dry soils and heat-waves.

We find that, in both events, persistent atmospheric pressure patterns induced land–atmosphere feedbacks that led to extreme temperatures. During daytime, heat was supplied by large-scale horizontal advection, warming of an increasingly desiccated land surface and enhanced entrainment of warm air into the atmospheric boundary layer. Overnight, the heat generated during the day was preserved in an anomalous kilometres-deep atmospheric layer located several hundred metres above the surface, available to re-enter the atmospheric boundary layer during the next diurnal cycle. This resulted in a progressive accumulation of heat over several days, which enhanced soil desiccation and led to further escalation in air temperatures.

Our findings suggest that the extreme temperatures in mega-heatwaves can be explained by the combined multi-day memory of the land surface and the atmospheric boundary layer.

Apr

2022

Effects of land-use change in the Amazon on precipitation are likely underestimated

Interesting article:

We found that the effect of column water vapor on hourly precipitation was strongly nonlinear, showing a steep increase in precipitation above a column water vapor content of around 60 mm. […] Although loss of tree transpiration from the Amazon causes a 13% drop in column water vapor, we found that it could result in a 55%–70% decrease in precipitation annually.

Consequences of this nonlinearity might be twofold: although the effects of deforestation may be underestimated, it also implies that forest restoration may be more effective for precipitation enhancement than previously assumed.

Apr

2022

The world’s forests do more than just store carbon, new research finds

I argued in my UNEP article “” about this… and more and more science seems to prove it: Forests cool the earth!

Researchers from the US and Colombia found that overall forests keep the planet at least half of a degree Celsius cooler when biophysical effects – from chemical compounds to turbulence and the reflection of light – are combined with carbon dioxide.

“Despite the mounting evidence that forests deliver myriad climate benefits, trees are still viewed just as sticks of carbon by many policymakers in the climate change arena. Forests are key to mitigation, but also adaptation.”