A practical exploration of land cover impacts on surface and air temperature when they are most consequential

Abstract

Widespread shifts in land cover and land management (LCLM) are being incentivized as tools to mitigate climate change, creating an urgent need for prognostic assessments of how LCLM impacts surface energy balance and temperature. Historically, observational studies have tended to focus on how LCLM impacts on surface temperature (Tsurf), usually at annual timescales. However, understanding the potential for LCLM change to confer climate adaptation benefits, or to produce unintended adverse consequences, requires careful consideration of impacts on both Tsurf and the near-surface air temperature (Ta,local) when they are most consequential for ecosystem and societal well-being (e.g., on hot summer days). Here, long-term data from 130 AmeriFlux towers distributed between 19-71 deg N are used to systematically explore LCLM impacts on both Tsurf and Ta,local, with an explicit focus on midday summer periods when adaptive cooling is arguably most needed. We observe profound impacts of LCLM on Tsurf at midday, frequently amounting to differences of 10 K or more from one site to the next. LCLM impacts on Ta,local are smaller but still significant, driving variation of 5-10 K across sites. The magnitude of LCLM impacts on both Tsurf and Ta,local is not well explained by plant functional type, climate regime, or albedo; however, we show that LCLM shifts that enhance ET or increase canopy height are likely to confer a local mid-day cooling benefit for both Tsurf and Ta,local most of the time. At night, LCLM impacts on temperature are much smaller, such that averaging across the diurnal cycle will underestimate the potential for land cover to mediate microclimate when the consequences for plant and human well-being are most stark. Finally, during especially hot periods, land cover impacts on Ta,local and Tsurf are less coordinated, and ecosystems that tend to cool the air during normal conditions may have a diminished capacity to do so when it is very hot. We end with a set of practical recommendations for future work evaluating the biophysical impacts and adaptation potential of LCLM shifts. 

Responses of Marginal and Intrinsic Water‐Use Efficiency to Changing Aridity Using FLUXNET Observations

“…In other words, IWUE under non‐equilibrium between canopies and atmosphere can be overestimated due to the higher VPD than the vapor pressure gradient near the canopy surface (i.e., the difference between intercellular vapor pressure ( e i ) and atmospheric vapor pressure ( e a ), e i – e a ). Difference between leaf and air temperature can also influence the e i – e a ; if leaf temperature is higher than air temperature (as it often is, e.g., Novick & Barnes, 2023; Yi et al., 2020), e i will increase while e a remains constant, resulting in larger e i – e a than measured VPD and consequently underestimate IWUE. Therefore, it is important to address this potential bias to quantify iWUE accurately.…”

Greening vegetation cools mean and extreme near-surface air temperature in China

“…Thus, our results only show the local effect of greening on SAT. However, greening vegetation in a certain pixel may cause non-local changes in circulation patterns, humidity and cloudiness that can feedback on local SAT [23,63]. The limitation of this method has less impact when studying LST, which is logically more relevant to local surface properties.…”

“…Compared to LST, SAT is a more widely used temperature metric in climate change research [17,18]. SAT is also more relevant to human, animal, and terrestrial ecosystem health than LST, as this temperature is directly experienced by humans [22][23][24]. SAT is closely related to LST but may substantially deviate from LST depending on both the atmospheric (e.g.…”

A Century of Reforestation Reduced Anthropogenic Warming in the Eastern United States

“…Toward this end, we specifically evaluated the difference between the tower‐derived temperature metrics and daily maximum T a estimates from the gridded 1 km Daymet product (Thornton et al., 2016), referred to as T s – T a . During the growing season, vegetated surfaces typically have higher surface temperature than air temperature, and thus a positive T s – T a (Mildrexler et al., 2011; Novick & Barnes, 2023). We anticipate a reduced T s – T a difference in forests due to their increased transpiration rates due to non‐forests, especially at midday when transpiration peaks.…”