Not that ET! The Terrestrial ET: EvapoTranspiration, the Unexplored Source of Climate Change
1 day ago Guest Blogger 26 Comments
By Charles Blaisdell, PhD ChE
Abstract
Evapotranspiration, ET, is a common term in agriculture used in connection with plant growth. ET: water going to the atmosphere from the earth’s surface. ET’s connection with climate change is described by the CRGW theory (def to follow) which starts out with a decrease in land ET (over time) that naturally (through the CRGW theory) leads to a global increase in ET. The localized land decrease in ET can occur in special parcels (urban heat islands,UHIs, deforestation, mining, etc) where the virgin land has been changed. The ET value of this change from virgin land is (in most cases) lost to time. Without an estimate of the change in ET over time the CRGW theory is not useful. This paper summarizes papers from Mazrooei et al. (2021) (1) and Lu Hao et al. (2021) (3) that present a creative method with NASA satellite data on local (urban Heat Islands, UHI’s) ET differences around the world. Their data (in climate change terms) show a wide range of ET that is correlated to the environment the UHI is in. Ariad UHI’s environments can have positive ET’s and wet environments have negative UHI ET’s. Mazrooei et al. (2021) uses a creative “bull’s eye” approach with satellite ET data. The UHI is in the center of the bull’s eye and the rural area in the outer ring. The ET from these two areas is used to calculate a precent difference in ET, showing a range of +10% to -50% and an average of -12% which may be a good estimate of the global UHI – virgin land difference.
The CRGW theory of ET related climate changes is: A localized ET decease (in a special parcel: UHI’s, deforestation, mining, etc.) = higher VPD (vapor pressure deficit) = air rising in a plume = less clouds or less reflective clouds = more sun = higher temperature and more evaporation of water = higher global ET: Cloud Reduction Global Warming, CRGW. In the CRGW theory the %ET/unit area difference between virgin land and special parcel remains about the same with time. What changes over time is the size of the special parcel (some albedo change may also occur). The result of this natural process can be seen in the current atmospheric “fingerprint” over time (1970 to 2020): Increasing temperature, increasing specific humidity, decreasing relative humidity, decreasing cloud fraction, and increasing VPD (vapor pressure deficit). The atmospheric “fingerprint” shows the end results of this theory but does not show the beginning ET decrease in a local area. We can see the current ET of a UHI but we will never know what the ET was before the UHI was there. The “fingerprint” is evidence that the sum total of all earths local (Special Parcel) ETs has decreased over the 1970 to 2020 period of time. The work of Mazrooei et al. (2021) (1) may be the closest we can estimate how much the ET of the earth has changed.
Introduction
Evapotranspiration, ET, is defined as the total amount water flux evaporated into the atmosphere from surface and plant (dew) Evaporation and plant Transpiration. ET is a term used in agriculture water management to aid in crop growth and is usually measured by monitoring soil moisture change over time and plant types. The units of measure are height of liquid water evaporated/unit time/area, mm/yr/m^2, etc. Atmospheric measurement of ET is best done by a “eddy covariance tower” (5) which uses relative humidity and temperature at several point to calculate local ET. Land/satellite-based ET calculation is quite complicated, see (4) and (12)for examples. The exploration of ET as a correlation to climate change is just beginning (7), (9), (11). The CRGW theory is only applicable to the period 1970 to present and uses the total global ET from land and oceans. Global ET vs time data currently has very short history, but significant progress is being made, (10). The limited data suggest global ET increasing over time. The following assumptions show that ET is related to specific Humidity, SH:
https://wattsupwiththat.com/2024/09/27/not-that-et-the-terrestrial-et-evapotranspiration-the-unexplored-source-of-climate-change/
