evapotranspiration

Oct

2023

Scientists prove clear link between deforestation and local drop in rainfall

Very important article on the link between deforestation, evapotranspiration and rainfall:

Even at a small scale, they found an impact, but the decline became more pronounced when the affected area was greater than 50km squared (2,500 sq km). At the largest measured scale of 200km squared (40,000 sq km), the study discovered rainfall was 0.25 percentage points lower each month for every 1 percentage point loss of forest.

This can enter into a vicious cycle, as reductions in rainfall lead to further forest loss, increased fire vulnerability and weaker carbon drawdown.

One of the authors, Prof Dominick Spracklen of the University of Leeds, said 25% to 50% of the rain that fell in the Amazon came from precipitation recycling by the trees. Although the forest is sometimes described as the “lungs of the world”, it functions far more like a heart that pumps water around the region.

He said the local impact of this reduced water recycling was far more obvious, immediate and persuasive to governments and corporations in the global south than arguments about carbon sequestration, which was seen as having more benefits to industrial countries in the northern hemisphere.

Jul

2022

Large-scale semi-arid afforestation can enhance precipitation and carbon sequestration potential

More forests, more rain: …that implementing measured characteristics of a successful semi-arid afforestation system (2000 ha, ~300 mm mean annual precipitation) over large areas (~200 million ha) of similar precipitation levels in the Sahel and North Australia leads to the weakening and shifting of regional low-level jets, enhancing moisture penetration and precipitation (+0.8 ± 0.1 mm d−1 over the Sahel and +0.4 ± 0.1 mm d−1 over North Australia), influencing areas larger than the original afforestation. These effects are associated with increasing root depth and surface roughness and with decreasing albedo. This results in enhanced evapotranspiration, surface cooling and the modification of the latitudinal temperature gradient. It is estimated that the carbon sequestration potential of such large-scale semi-arid afforestation can be on the order of ~10% of the global carbon sink of the land biosphere and would overwhelm any biogeophysical warming effects within ~6 years.

Jul

2022

New definitions for moisture recycling and the relationship with land-use changes in the Sahel

Evapotranspiration: In the Sahel, recycling of moisture through evapotranspiration appears to be responsible for more than 90% of the rainfall. As a result, there exists an important feedback mechanism between land-use and climate, which has immediate implications for the management of natural resources.

Jul

2022

Megacity precipitationsheds reveal teleconnected water security challenges

Megacities depend on downwind evapotranspiration: Our results reveal that 19 of 29 megacities depend for more than a third of their water supply on evaporation from land. We also show that for many of the megacities, the terrestrial dependence is higher in dry years. This high dependence on terrestrial evaporation for their precipitation exposes these cities to potential land-use change that could reduce the evaporation that generates precipitation. […] reveals four highly vulnerable megacities (Karachi, Shanghai, Wuhan, and Chongqing). A further six megacities were found to have medium vulnerability with regard to their water supply.

Jun

2022

Presentation: Working with plants, soils and water to cool the climate and rehydrate Earth’s landscapes

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).

Jun

2022

Article: Working with plants, soils and water to cool the climate and rehydrate Earth’s landscapes

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).

Jun

2022

The impact of global land-cover change on the terrestrial water cycle

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.

Jun

2022

Human modification of global water vapor flows from the land surface

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.

Jun

2022

Land use and land cover changes and their impacts on surface-atmosphere interactions in Brazil: A systematic review

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.