The impact of urban activities and air pollution
on precipitation amount and distribution
There is much talk about the greenhouse gases and their relation to the
global change. In most part, scientific attention was drawn towards the
research about the heating of the planet. Now it is becoming clear that Air
pollution, which directly increases the number of CCN and thus, the number
of cloud droplets, shows evident relation with precipitation. This effect has
not been equally discussed. One reason this issue was skipped over is the
lack of tools for measuring and assessment of the emission of polluting
aerosols on the global precipitation formation processes. In the Hebrew
University, we devised a method to deduct the microphysical properties of
clouds and the precipitation formation processes over large areas from
meteorological satellite data.
In dense populated areas in the world, changes in the composition of clouds
can be observed, which suggest a decrease in the efficiency of precipitation
formation is evident in almost every satellite image. By this kind of
processing combined with computer imaging, we can practically ‘see’ how
man causes the changes in one of the most important pillars of our climate –
Rain.
The development and application of this method allowed us, for the first time,
to evaluate the influence of natural and anthropogenic pollution on the
formation of precipitation. The first findings point the possibility that aerosol
Air pollution has an negative influence on rain, mainly in densely populated
areas, which are mostly dependent upon rain.
From further analysis we have conducted, which combine climatological and
synoptic data from urban and rural areas in California, USA, the influence of
air pollution on rain was apparent [see appendix]. These results show a
decrease of 15% in the rain amounts measured in mountainous areas
downwind from big urban centers over the last 120 years. In the past 20
years there has been a major decrease in pollution values, thanks to
preventive legislation by the local authorities in California. In accordance to
this improvement we also found the precipitation decrease is more
moderated.
Deploying the technology described above and the results from the research
in California that demonstrate the physical theory, we suggest a similar
research should be performed on the climatological and synoptic data
acquired in Israel. The research will examine the trends of rain in yearly
series in areas with different geography – the polluted coastal area - Tel
Aviv metropolin versus the areas downwind to the pollution sources Judeah and Semaria mountains.
In order to differ the human influencing factors and the natural ones (like
changes in the wind component) a physical model will be introduced based
on radiosonde data from Beit Dagan meteorological station. Based on data
of the coastal windflow, precipitation and mixing ratio, this model will
simulate the average daily precipitaion, which is expected in the
mountainous areas of the research not showing the pollution effects.
By understanding the effect of pollution on the efficiency of precipitation in
Israel, we could gain awareness for the problems caused by Air pollution.
This knowledge can also contribute to the promotion of new methods for rain
enhancement as cloud seeding using matter that neutralizes the negative
effects.