Disappearing groundwater requires action to prevent widespread water scarcity
Groundwater is the primary water source for billions of people and for nearly half of irrigated agriculture, yet its incon- spicuous presence has allowed groundwater to elude effective governance and manage- ment in countless regions around the world. Consequently, more than half of the world’s major aquifers are being depleted, some of them at an alarming pace.
More forest, more stable rains:
We found a significant buffering effect of forests in the precipitation variability of 10 out of 14 biomes globally. On average, if 50% of precipitation originates from forest, then we find a reduction in the coefficient of variation of monthly precipitation of 60%. We also observed that a high fraction of precipitation from non-forest land sources tends to have the opposite effect, that is, no buffering effect. The average variation of monthly precipitation was 69% higher in areas where 50% of precipitation originates from non-forest land sources in the precipitationshed. Our results emphasize the importance of land cover composition in the precipitationshed to buffer precipitation variability downwind, in particular forest cover.
Forests and their impacts on low level clouds:
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.
My presentation on “Working with plants, soils and water to cool the climate and rehydrate Earth’s landscapes“.
As it looks, we have a pretty exciting tool in the climate as well as agriculture discussion with multiple benefits: more vegetation (especially in agriculture; through undersowing, intercropping, agroforestry, but also through a different form of animal husbandry, forest conversion, water retention) means more fertile soils, more water storage capacity and infiltration, more nutrients, more habitat for insects & co, more … and v. especially a cooling (of the layers near the ground), heat loss into space, more clouds with more precipitation and more sunlight reflection, which in turn contributes to the cooling of the climate, as well as activates the small (weakened) water cycles.
In short, we can(t) work with nature to cool the climate, strengthen the small water cycles, and in the process make agriculture, forestry, and water management more resilient and “fertile.”
This talk is based on the findings of my UNEP article (exists in French, Spanish, Chinese too).
Interesting analysis:
Here, we carefully analyze the situation for reforestation and afforestation (R&A) at midlatitudes, where the warming effects due to vegetation albedo are regarded to be almost balanced by the cooling effects from an increased carbon storage. Using both satellite data and atmospheric boundary-layer models, we show that by including cloudalbedo effects due to land–atmosphere interactions, the R&A cooling at midlatitudes becomes prevalent. This points to a much greater potential of R&A for wet temperate regions than previously considered.
My UNEP paper on “Working with plants, soils and water to cool the climate and rehydrate Earth’s landscapes“.
The continued destruction of forests, the deterioration of soils, the subsequent loss of terrestrial soil water storage and the reduction of water retention in the landscape are disrupting the movement of water in and through the atmosphere. This disruption causes major shifts in precipitation that could lead to less rainfall and more droughts in many areas of the world, increases in regional temperatures and an exacerbation of climate change. These changes affect regional climate, but can also impact regions far away. Understanding the interwoven relationships and the subsequent fluxes of energy between plants, soils and water on the ground, as well as in the atmosphere, can help mitigate climate change and create more resilient ecosystems.
Translations into French, Spanish, Chinese to be found here (#25).
Vicious cycle of destruction in the Amazon:
Here we show that the risk of self-amplified Amazon forest loss increases nonlinearly with dry-season intensification. […] Our results suggest that the risk of self-amplified forest loss is reduced with increasing heterogeneity in the response of forest patches to reduced rainfall. […] Although our findings do not indicate that the projected rainfall changes for the end of the twenty-first century will lead to complete Amazon dieback, they suggest that frequent extreme drought events have the potential to destabilize large parts of the Amazon forest.
Yesterday, at gentle 24 ° C air temperature, I measured the soil surface temperatures (for the first time). On the areas with open soil in the corn field of our neighbour: over 50°C. In the clover grass on our side: 26°C.
It’s amazing how the soil heats up (and was another 6°C warmer than the (rough) road next to it). Problematic not only for the soil life, soil water and for many crops. Also not good for the climate, because of warming of air temperature in this area, increased heat radiation, on larger areas potential development of high pressure areas, possible reduction of precipitation, … For more see my UNEP article and presentation, and the Climate Landscapes conference.
Human induced changes on the terrestrial water cycle:
Geographic modelling reveals that land-cover change reduces annual total evapotranspiration by approximately 3,500 km3/yr (5%) and that the largest changes in evapotranspiration are associated with wetlands and reservoirs. Land surface model simulations support these evapotranspiration changes, and project increased runoff (7.6%) as a result of land-cover changes. […] The results demonstrate that land-cover change alters annual global runoff to a similar or greater extent than other major drivers, affirming the important role of land-cover change in the Earth System.
Deforestation and the global water cycle:
We show that deforestation is as large a driving force as irrigation in terms of changes in the hydrological cycle. Deforestation has decreased global vapor flows from land by 4% (3,000 km3/yr), a decrease that is quantitatively as large as the increased vapor flow caused by irrigation (2,600 km3/yr). Although the net change in global vapor flows is close to zero, the spatial distributions of deforestation and irrigation are different, leading to major regional transformations of vapor-flow patterns. We analyze these changes in the light of future landuse-change projections that suggest widespread deforestation in sub-Saharan Africa and intensification of agricultural production in the Asian monsoon region. Furthermore, significant modification of vapor flows in the lands around the Indian Ocean basin will increase the risk for changes in the behavior of the Asian monsoon system.
Green water — terrestrial precipitation, evaporation and soil moisture — is fundamental to Earth system dynamics and is now extensively perturbed by human pressures at continental to planetary scales. However, green water lacks explicit consideration in the existing planetary boundaries framework that demarcates a global safe operating space for humanity.
The green water planetary boundary can be represented by the percentage of ice-free land area on which root-zone soil moisture deviates from Holocene variability for any month of the year. Provisional estimates […] indicate that the green water planetary boundary is already transgressed.
Earlier vegetation greening under climate change raises evapotranspiration and thus lowers spring soil moisture. […] We provide observational evidence that increased foliage cover over the Northern Hemisphere, during 1982–2011, triggers an additional soil moisture deficit that is further carried over into summer. […] attribute the driving process to be larger increases in evapotranspiration than in precipitation. This extra soil drying is projected to amplify the frequency and intensity of summer heatwaves. Most feedbacks operate locally, except for a notable teleconnection where extra moisture transpired over Europe is transported to central Siberia. Model results illustrate that this teleconnection offsets Siberian soil moisture losses from local spring greening.
Major land use and land cover changes in Brazil and their impacts on precipitation and evapotranspiration:
For the Amazon biome, decreasing dry season P and in annual ET were reported. In the Cerrado biome, decreasing P in the wet and dry seasons and decreasing dry season ET were the most common result. For the Atlantic Forest biome, increasing annual P and increasing wet season ET, likely due to reforestation, were reported.
Nature is incredibly complex. My feeling in general is that we should imitate the natural systems as much as possible. In one study on the shifts of regional water availability due to global tree restoration the authors come to the conclusion:
Large-scale tree-cover expansion can increase water availability by up to 6% in some regions, while decreasing it by up to 38% in others. There is a divergent impact on large river basins: some rivers could lose 6% of their streamflow due to enhanced evaporation, while for other rivers, the greater evaporation is counterbalanced by more moisture recycling.
Difficult thing: Should we consider planting forests where forests have been before, even if water availability is decreasing (after the models)? What are other impacts of planted forests? More humidity in the air, more water circulation, more precipitation somewhere else?
Very good article on the functioning of soil life and its importance for plant growth, the water cycle and the planet´s health.
I am organising an international online event “Climate Landscapes”, 18.-19.10.2022. Many well-known scientists from various fields have already agreed to be part of the conference, which is really great.
My aim however is not to organise yet another scientific conference, but one where different players/stakeholders in society will get together, get in contact and talk to each other, across disciplines and “sectors”. Thus, I want there many representatives from other-then-research to be present.
My question(s) to you is/are:
Best wishes,
Stefan
PS: “Working with plants, soils and water to cool the climate and rehydrate Earth’s landscapes”: my UNEP paper; my presentation.
“Italy’s Po River flows some 650km from the snowy Alps in the northwest to the wild Po Delta in the east before rushing out into the Adriatic Sea.
During its course, the great waterway nourishes the expansive fertile plains of northern Italy where farmers have thrived for generations. Dubbed Italy’s breadbasket, these flatlands covered with crops are responsible for some 40 per cent of Italy’s GDP.
At the moment, however, the normally life-giving waters of the Po River have suddenly become an unexpected threat. The dramatically low water levels of the river have been causing seawater to be sucked back upstream.”
Source: Euronews
The Aqueduct Water Risk Atlas: “Water risks are an urgent global challenge. Most public health crises are already driven by water, including floods, droughts and water-borne diseases. Climate change is worsening the problem by intensifying floods and drought, shifting precipitation patterns, altering water supplies and accelerating glacial melt and sea level rise. Clean water supplies are vital for human health, industry, agriculture and energy production, making water risks a major humanitarian threat. Identifying, understanding and responding to these risks requires transparent, publicly available data.”
Agriculture is the biggest degrader of land, the authors say. Transforming farming practices could restore billions of acres by 2050 for less than is spent on developed-world farm subsidies.
New research shows forest restoration schemes should prioritise restoring native forests for greatest climate and environmental benefits. However these benefits have a trade-off with wood production in comparison with tree plantations.
The faster growth of trees in plantations managed for timber or pulp production implies greater uptake of water from the soil, which leaves less water for replenishing the groundwater reserves that sustain streams, especially in drier areas. To make matters worse, trees in such plantations are typically harvested more frequently than those in native forests, leading to greater soil disturbance and poorer streamflow regulation.”