Guest Post by Willis Eschenbach [See Update At The End]
I keep reading that one of the things that we are already seeing (or that is predicted) is that the wet areas of the planet are getting wetter and the dry areas are getting drier, viz:
May 31, 2017 – As the world warms due to human-induced climate change, many scientists have been … summer, wet areas will get wetter and dry areas will get drier. … United States, inner Asia and the Middle East will become even dryer.
NOAA GFDL Climate Research Highlights Image Gallery Will the Wet Get Wetter … in precipitation near 20°S and 20°N – latitudes in the subtropical dry zones.
Wet regions getting wetter, dry regions drier as planet warms … simulations of the climate show reductions in rainfall over the drier tropical land regions … that drying of the drier regions continues (right) while wet regions will experience more …
Dec 12, 2016 – The world’s wet regions are getting wetter and the dry regions are … warming climate; as the world gets warmer wet regions will continue to get …
May 21, 2012 – … get richer’ mechanism, where wet regions get wetter and dry regions drier. … “Salinity shifts in the ocean confirm climate and the global water …
I thought about that while reading a recent study called Rapid Drying of Northeast India in the Last Three Decades: Climate Change or Natural Variability?. (Their conclusion, by the way, was that it was NOT from human actions, but instead that “the recent decreasing trend of NEI summer monsoon rainfall is, rather associated with the strong interdecadal variability of the subtropical Pacific Ocean“.)
So I went to the marvelous KNMI Climate Explorer and got the CRU TS 4.01 gridded precipitation dataset, which covers from 1901 through 2016. I started by looking at the trend of the data since 1901.
Figure 1. Global rainfall, land-only, 1901 – 2016.
Now, there is a trend … but the increase in monthly rainfall is only 2 millimeters per century. This represents an increase of about an inch (25 mm) in the yearly average rainfall. Small.
Next, since the Indian study concerned the recent decades, I looked more closely at the average rainfall over that period. Figure 2 shows the average rainfall around the globe for the period 1980 through 2016.
Figure 2. Average rainfall, 1980 – 2016. Rainfall is shown on a 1° latitude by 1° longitude gridcell basis. All areas with over 2.2 metres/year are shown in darkest blue.
Here you can see the great deserts of the Sahara, the Gobi, the Atacama, and central Australia. You can also see the wet zones of the Amazon, the African rainforests, and Indonesia and Papua New Guinea.
Next, I looked at the individual trends for each 1°x1° gridcell over that same period, from 1980 through 2016.
Figure 3. Precipitation trends, monthly precipitation, millimeters/month per decade. Areas with trends greater than 7 or less than -7 mm/decade are shown in bright blue or bright red. Click to embiggen.
Here we can see the problem indicated in the Indian study, the drying of Northeast India.
Finally, using the combination of precipitation and precipitation trend data, we can see if it is true that the dry areas are getting drier and the wet areas are getting wetter. Figure 4 shows a scatterplot of the two datasets.
Figure 4. Scatterplot, average land-only annual precipitation versus precipitation trend, 1980 – 2017. The black dots with whisker lines show the median and the error range for that precipitation interval.
What this shows is that while the wetter areas are getting wetter, it is not true that the drier areas are getting drier. On average, all areas are getting more rain. Not a lot more rain, of course, but more rain. Once again, the climate models are wrong.
And so one more beautiful climate myth runs aground on a reef of hard facts … the wet is getting wetter, but the dry isn’t getting drier—instead, the dry is getting wetter as well
[UPDATE] I realized that I had another dataset showing rainfall. This is the Tropical Rainfall Measuring Mission satellite rainfall dataset. Here is what that looks like.
Figure 5. Movie loop of the monthly averages of the tropical rainfall, Dec 1997 – Mar 2015. The coverage of the mission only extends from 40°N to 40°S. Note that this covers about two-thirds of the surface of the planet. Units are mm/month.
I ran the same type of scatterplot analysis on this data as in Figure 4, and I got the same results.
Figure 6. Scatterplot, TRMM data, average 40°N to 40°S annual precipitation versus precipitation trend, 1997 – 2015. The black dots with whisker lines show the median and the error range for that precipitation interval.
On average, wet areas are getting wetter, and dry areas are getting wetter as well. Go figure …
Finally, note the wide spread of the data. There are many dry areas getting wetter, and many wet areas getting drier. However, on average they are all either staying the same or getting wetter.
Here, we’re in the “wetter” part of the equation, a rainy Christmas Eve. Well, since it’s 2:03 AM, I guess it’s actually a rainy Christmas morning … so the very best of wet Christmas morning wishes to everyone.