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Abstract:
Generally, surface and air temperatures seem closely related but we show that they respond
differently to evaporative conditions. We evaluate the temperature increase in response to solar radiation
for different evaporative fractions, using observations from the Southern Great Plains. The warming rate of
air temperature decreases only by 1.7 × 10−3 K/(Wm−2) from dry to moist conditions compared to a stronger
reduction by 14 × 10−3 K/(W m−2) for surface temperature. The weaker response of air temperature to
evaporative fraction is explained by the larger growth of boundary layer on drier days, which suppresses the
warming of air. Estimates based on this explanation reproduce the warming rate of air temperature in
observations. Our results show that diurnal variations of surface temperatures contain imprints of
evapotranspiration while air temperatures do not. These findings appear important to be considered when
using, analyzing, or interpreting temperature data in studies dealing with climate change, hydrology, or
land‐atmosphere interactions. Surface and air temperatures are measured just 2m apart, so it might
seem that they carry the same information. Here we show that these temperature measurements respond
rather differently to whether the surface evaporates or not. To show this, we use data from a well‐equipped
measurement site in the Central United States and calculate the rates by which the surface and the air warm
in response to solar radiation. We found that the surface temperature responds about 8 times stronger to
evaporation than air temperature. We explain this weaker response of air temperature by the stronger
growth of the boundary layer without evaporation. This results in a deeper, well‐mixed boundary layer that
does not warm as strongly. What our results imply is that evaporation may be inferred from surface temperatures, but not from air temperatures.
