Saturday, May 21, 2016

Is the Dry Zone becoming a Wet Zone

 Many Sri Lankans may remember from school geography the Dry Zone of Sri Lanka is from North West (Puttalam) to East (Batticoloa) and South East (Hambanthota).  In this area rain is received only from the North East (NE) monsoon, i.e. mid-late October to January.  May to November is dry with hardly any rain.

Has this changed. Last year (2015) there was moderate rain even in June, in the North West (Puttalam).  This year (2016) it has been heavy rains and floods in mid May and more expected at the end of May as well. So will the Dry Zone, at very least NW have rains in the coming years during the historical dry season. At very least during El Nino year, it is still El Nino conditions this year.
I think so, Sri Lanka is going to have rain and lots of it.  Why, because
  • The Indian ocean is warming up
  • Air temperature is warming
  • Water Vapor in Atmosphere
  • Amount of Water Carrying capacity increases exponentially.
The critical physics is Water carrying capacity (saturation)  of the Atmosphere.  That is the amount of water vapor that the atmosphere can hold at any given temperature.  This amount of water vapor that atmosphere can hold increases very quickly after about 30°C.

So with the air temperature increasing, the Indian ocean warming up,  there is going to be a lot more water vapor in the atmosphere. Specially above Sri Lanka because we are an Island.  So all that increased water vapor in the atmosphere comes down in a deluge, i.e. buckets of water not raindrops.

Is it possible during the SW monsoon, there is so much water in the atmosphere now, part of it get carried over into the Dry Zone.  Just like the more intense NE monsoon rainfall getting carried over to the wet zone.

This property (Wilpattu House) was bought in Sep 2011.  I was told the last time that the Lunu Ela (river bordering the property) was 20 years ago.  However, there has been a flood of the Lunu Ela every year in December, except 2013.  This year, even in May.  Old timers say never during their lifetime floods, let alone heavy rains in May.

One may well argue whether Climate Change is man made or natural occurrence.  If one thinks it is because of humans, the results of whatever mitigation (e.g. less Fossil Fuel, re forestation)  will be seen many many year later.   At the moment Climate Change is here to stay for the next few decades.

What is needed is how do we work around the effects of climate change.  For instance, flooding in Colombo will be the norm.  What kind of infra structure is needed (e.g. canals) to reduce or eliminate flooding in Colombo.  Warning systems for Landslides.  What kind of crops can handle flooding and heavy rains. Thats whats needed at the moment, not discussions of reducing fossil fuels and changing to solar power (all very good).

A comment I made in 2010

If you think in general that air temperatures have increased, you will see larger increases in rain (precipitation).
The reason is that the water holding capacity of air increases exponentially with increasing temperature. i.e. Small increases in air temperature at around 38-40C will have much larger increases in water holding capacity. See link below.
Water Vapor .
Bottom Line: Expect Deluges to be the norm even in the North East.