Page 11 - Perspective Paper

in vegetal biomass – particularly in regions with high Vegetation-regulated Moisture Recycling (VMR) – can
have critical effects on the amount downwind precipitation (Keys et al., 2016).

The combined effects of land cover changes thus have widespread implications for weather and climate
dynamics (Anthes, 1984). The myriad effects from land cover change often have opposing signs in radiative
forcing, making their combined feedbacks critical for understanding the net climate impact (Bright et al.,
2015). Integrating all the physical effects of land degradation and restoration remains a challenge. Site-
specific atmosphere–biosphere interactions and feedbacks should be considered with respect to their local
and global impacts. Efforts to regain losses in structure and functioning of land surfaces must take on a
predictive and proactive approach, based on an understanding of the local water cycle and the root causes
of degradation, and a recognition of the nonstationary nature and uncertainty of climate trends (Milly et al.,
2008).

The forcing and feedback from changes in the sensible heat flux due to the degradation of the biosphere has
been hidden in the shadow of the dominant CO2/GHG narrative. Studies show that land cover changes and
the resultant energy balance perturbations have had significant impacts on the global water cycle (Wang-
Erlandsson et al., 2022) and the atmospheric energy budget (Duveiller et al., 2018). For example, land use
change is a dominant contributor to global-mean temperature and precipitation change through alterations
of the latent and sensible heat fluxes (Mahmood et al., 2013; Perugini et al., 2017) as well as a driver in
changing climate extremes (Sy & Quesada, 2020). The regional and global effects of landscape conversion
are inherently location-dependent (Mahmood et al., 2013), and there is still a high level of uncertainty in
quantifying these effects (Perugini et al., 2017). As such, we must avoid basing actions entirely on generalised
statements on the benefits or drawbacks of re- or afforestation, but rather on site-specific research that
reveals the coupling between ecosystem dynamics and global climate feedbacks (Mahmood et al., 2013).

3.2 Atmospheric moisture recycling and terrestrial precipitation

Freshwater scarcity is one of humanity’s most pressing issues, which has not only left billions without
adequate access to drinking water, but also threatens our global food security and heightens the risk of social
conflicts and increases the spread of diseases (Gleick & Cooley, 2021). Precipitation is the only sustainable
fresh water source that exists and thus the promotion of precipitation across terrestrial surfaces is crucial
towards ensuring reliable access to freshwater. There is no ‘one-size-fits-all’ approach to enhance
precipitation on land because of the heterogeneity of surface conditions such as orography, distance to coast
and mean insolation. Precipitation is, however, a function of a number of distinct factors that can be
leveraged in order to produce the environmental conditions for precipitation to occur, one of which is
evaporation (Anthes, 1984).

In the past, biogeographers generally assumed that local precipitation is an external variable that is not
influenced by vegetation (van Noordwijk & Ellison, 2019), but an increasing number of studies have now
proven this assumption to be incorrect (Alton et al., 2009; Ellison et al., 2017; Gong et al., 2017; Keys et al.,
2017; Makarieva et al., 2013; Millán et al., 2005; Savenije, 1995, 1996; te Wierik et al., 2021; van der Ent et
al., 2010; Wang-Erlandsson et al., 2014). The mechanistic role of vegetation reduction on drought spells
(Savenije, 1995) and the role that terrestrial vegetation plays in transporting moisture from oceanic origin
land inwards (Keys et al., 2016; Makarieva et al., 2013) are two highly relevant findings that may be the key
to restoring rainfall.

A ‘precipitation shed’ describes spatial origin of moisture (where it has evaporated from) that falls as rain in
a specific location (van der Ent et al., 2010). An understanding of the origin of moisture opens up
opportunities to improve governance of the global distribution of water, but also allows for strategic action
towards water cycle regeneration. In continental catchments moist airmasses (‘sea breeze’) are formed over
water bodies and travel across terrestrial surfaces, the added moisture through evapotranspiration from land

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