Precipitation Patterns due to Global Heating

L. David Roper
http://www.roperld.com/personal/roperldavid.htmhttp://www.roperld.com/personal/roperldavid.htm
6 April, 2016

Contents

Introduction

Global Heating causes more moisture to be evaporated into the atmosphere from land and seas. Therefore, the average precipitation over the Earth increases as global heating increases.

Therefore, it is expected that land masses whose area is small compared to its boundary with seas should have the most increase in precipitation as global heating increases. And land masses whose area is large compared to its boundary with seas may decrease in precipitation as global heating increases.

These rules may not hold in every case; prevailing winds and the existence of mountain ranges may have large effects.

Precipitation data are taken from http://bonnet19.cs.qc.edu:7778/pls/rschdata/rd_start.main. Precipipation data for early times are sparse; so preference is given to data for later times. Usually there are many sites in a country for which data are available. The median is calculated for the twelve months of each year for a site. Sites are eliminated that are missing three months of data. Then, the median of all the sites is calculated for each year.

Yearly precipitation is plotted for the monthly median times 12. Another option would be to plot the monthly sums plus the monthly median times the number of missing months. It does not change the results very much to use this option.

I do not understand the unit of precipitation given (mm/year); that appears to be much too small a unit. I am considering the unit as arbitrary.

In the precipitation graphs that follow, a linear fit to the data and its equation are shown.

Countries studied: Australia, Brazil, Canada, Chad, Chile, China, Cuba, Czech Republic, Ireland, United Kingdom, United States, Mexico, India, New Zealand, Madagaskar, Mongolia, Iceland, Greenland, Russia (Europe), Japan, Italy, Spain, South Africa

Countries with Small Area Compared to Sea Boundary

First consider countries with small area compared to sea boundary. The following islands have increasing precipitation, as expected:

Mexico
The rise in precipitation is as expected for global warming, because of ratio of shoreline to area.
United Kingdom and Ireland
The rise in precipitation is as expected for global warming, because of ratio of shoreline to area.
It appears that the U.K. provides some shielding from North-Sea-caused precipitation
Japan

The rise in precipitation is as expected for global warming, because of ratio of shoreline to area.
New Zealand

The rise in precipitation is as expected for global warming, because of ratio of shoreline to area.
Iceland
The rise in precipitation is as expected for global warming, because of ratio of shoreline to area.
Greenland
The rise in precipitation is as expected for global warming, because of ratio of shoreline to area.

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The following islands have decreasing precipitation, apparently because the prevailing wind is off a large land mass to the west instead of the water to their east:

Cuba
This appears to be an anomoly, as the ratio of shoreline to area should cause the precipitation to increase. Perhaps the North American and Central American land masses cause the precipitation to decrease.
Madagaskar
It appears that the African land mass causes the precipitation to decrease.

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Countries with Large Area Compared to Sea Boundary

In general we expect these countries to have decreasing precipitation with time. The follow do:

United States
The large ratio of area to shoreline causes declining precipitation due to global warming.
China

The large ratio of area to shoreline causes declining precipitation due to global warming. China is in dire straits with rapidly declining precipitation.
Brazil
The large ratio of area to shoreline causes declining precipitation due to global warming.
South Africa

The large ratio of area to shoreline causes declining precipitation due to global warming.
Russia (Europe)
The large ratio of area to shoreline causes declining precipitation due to global warming.

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Spain
Despite the fact that Spain has water on the north, west and east, it has decreasing precipitation with time. I suspect that this has to do with prevailing winds from North Africa.

Countries with Large Area and Large Shoreline

There are some large countries that have steady or increasing precipitation with time, mostly because of large bodies of water around them:

Canada
The ratio of area to shoreline is not large.
Italy
Chile
India
India's large land mass almost balances its water boundaries.
Australia
Australia is an exception. Perhaps the large Asian land mass to the north conteracts the water masses that surround Australia

Land-Bound Countries

Global heating, without extenuating circumstances, should cause precipitation to decrease for land-bound countries.

Chad
The data are rather poor.
Mongolia
Czech Republic
It appears that the global-heating effect was not operative until about 1950, and then only weakly.

Precipitation versus Land-Area/Coast-Length Ratio

This section is to test if the change in precipitation is a function the land/area to coast-length ratio. The following data for land areas were taken from Wikipedia.org and the coast lengths were roughly measured using the Microsoft Streets and Trips program:

Country
Coast length (10^3 miles)
Area (10^6 mi^2):
Ratio (miles):
Precip. Slope
Cuba
1.5
0.042
28.3
-0.1986
Iceland
1.2
0.040
33.1
0.2427
Ireland
0.85
0.033
38.3
0.0157
NZealand
2.6
0.103
39.8
0.1488
Japan
3.05
0.146
47.8
0.0582
UK
1.95
0.094
48.2
0.08887
Spain
1.84
0.195
106.2
0.0357
Greenland
4.3
0.836
194.4
0.1562
Mexico
3.7
0.762
205.8
0.062
SAfrica
1.55
0.471
304.2
-0.0595
Australia
8.15
2.941
360.9
-0.0674
India
2.9
1.269
437.7
0.0398
USA
5
3.131
626.2
-0.1063
Brazil
4.1
3.288
801.9
-0.2471
China
2.35
3.758
1599.1
-0.7224
Exclude:
Canada
4.6
3.854
837.8
2.9139
Italy
2.05
0.116
56.8
0.4661
Chili
3.1
0.292
94.3
0.5512
Madagaskar
2.3
0.227
98.5
-0.5302

I have almost zero confidence in the Canada coast length that I measured, since their is so much inland water in northern Canada; therefore, I exclude Canada from the study.

The following graphs show the (precipitation slope for the linear fits to the precipitation versus time) versus (Area/Coast ratio in miles):

This shows that Italy, Chili and Madagaskar are outliers, probably because they are narrow pieces of land. So I exclude them in the next graph.

Both graphs have about the same linear slope. The linear fit is quite good.

Conclusion

The data shown above fit the theory of increased evaporation and, thus, precipitation due to global heating.

Although, for example, precipitation has decreased for the United States, it probably increased along the coasts. Therefore, it probably decreased even more in the central part, the "breadbasket".

China is in dire straits with rapidly declining precipitation.

References

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Roper Global-Heating Web Pages
L. David Roper interdisciplinary studies