Wet Get Wetter?
The climate change phrase the wet get wetter, the dry get drier appears to originate with the 2006 paper by Held and Soden entitled Robust Responses of the Hydrological Cycle to Global Warming. The actual verbiage from that paper: “In contrast, assuming that the lower-tropospheric relative humidity is unchanged and that the flow is unchanged, the poleward vapor transport and the pattern of evaporation minus precipitation (E − P) increases proportionally to the lower-tropospheric vapor, and in this sense wet regions get wetter and dry regions drier.”
A decade later, a 2016 paper by Byrne and O’Gorman(2016) entitled The Response of Precipitation Minus Evapotranspiration to Climate Warming: Why the “Wet-Get-Wetter, Dry-Get-Drier” Scaling Does Not Hold over Land.
In the previous post on Climate Observer, “Past Climate Change Predictions”, I noted the frustrating lack of observational data against which to evaluate modeled precipitation, evaporation, soil moisture and runoff. Uncertainty aside, I have plotted the ERA5 reanalysis estimates of precipitation and evaporation and the P-E difference below. Again, these values are not strictly observational data, but reanlysis.
For the reanalysis over the period 1979 through 2021, changes are greater over ocean than land. Precipitation over ocean indicates a large increase at lobes of the ITCZ maxima near the equator. Evaporation increases exist from roughly 45S to 45N. The change of precipitation evaporation difference over the oceans indicates an increase near the Northern ITCZ and decreases in the subtropics. Higher latitudes exhibit little change in P-E difference.
Over land, the largest change appears to be a decrease of precipitation around 30S and also around 5N. Other latitudes indicate small changes. Evaporation over land indicates a decrease around 30S and little change elsewhere.
Byrne, M. P., & O’Gorman, P. A. (2015). The Response of Precipitation Minus Evapotranspiration to Climate Warming: Why the “Wet-Get-Wetter, Dry-Get-Drier” Scaling Does Not Hold over Land, Journal of Climate, 28(20), 8078-8092. Retrieved May 20, 2022, from https://journals.ametsoc.org/view/journals/clim/28/20/jcli-d-15-0369.1.xml
Copernicus Climate Change Service (C3S) (2017): ERA5: Fifth generation of ECMWF atmospheric reanalyses of the global climate, Copernicus Climate Change Service Climate Data Store (CDS), accessed May 6, 2020, https://cds.climate.copernicus.eu/cdsapp#!/home.
Held, I. M., & Soden, B. J. (2006). Robust Responses of the Hydrological Cycle to Global Warming, Journal of Climate, 19(21), 5686-5699. Retrieved May 20, 2022, from https://journals.ametsoc.org/view/journals/clim/19/21/jcli3990.1.xml