Reportedly North Sumatra has a distinct wet season and dry season. The wet season starting in November and lasting for 6 months till the end of April. I don’t know about North Sumatra, Berastagi, Bukit Lawang, or Parapat but I am getting a bit of idea about the weather in part of Tuk Tuk. This does not necessarily mean that this holds for Samosir or even the rest of Tuk Tuk. I am talking about the South Bay of Lake Toba in Tuk Tuk, this is the area where you find Liberta, Bagus Bay, Horas Family Home and Tabo Cottages.
Location Horas Family Home in Tuk Tuk Rain in the afternoon
I have now measured the rainfall at Horas Family Home on a daily basis over the last 12 years and find that what I measured does not support the Statement of a six months wet season – dry season cycle.
For my recordings I follow my definition of the Hydrological Year in Tuk Tuk, which means that my Hydrological Year starts with the reportedly wet season in Tuk Tuk, being November 1.
Of course the data is averaged over a 12 year period and there can be quite a difference in rainfall during a month from year to year. So far I found the driest month to be July 2014 with 0 mm, directly followed by February 2010 with only 16 mm, in the wet season, and the wettest month August 2008 with 469 mm, in the dry season.
The wettest February brought 251 mm and the driest August 58 mm
Notwithstanding the wide range per month, the yearly average was very close from November 2007 till October 2013.
November 2007 – October 2008 2054
November 2008 – October 2009 2116
November 2009 – October 2010 2061
November 2010 – October 2011 1969
November 2011 – October 2012 2150
November 2012 – October 2013 2194
November 2013 - October 2014 1857
November 2014 - October 2015 1879
November 2015 - October 2016 1464
November 2016 - October 2017 1789
November 2017 - October 2018 2244
November 2018 - October 2019 2029
So as compared to the years before the year Nov 2013 - Oct 2014 was already very dry, even to the extend that it affected crops and paddy grow. however, the difference with the average of 200 mm amounts to 10%, which is well within the range of plus or minus the normal standard deviation. So as far as that goes nothing to worry about.
The year Nov 2014 - Oct 2015 was as dry as the year before Nov 2013 - Oct 2014. The last year November 2015 - Oct 2016 beats all my records with only 1464 mm. The year November 2016 - Oct 2017 is also very dry. The start of the wet season was extremely dry, but the months August and September ended up well above average.
The last 2 years were above or about the average so maybe we are back to normal.
Effect of rainfall on the water level in Lake Toba.
For most of the time there is no direct relation between rainfall and the water level of Lake Toba as the water level in Lake Toba is the result from:
Direct rainfall in Lake Toba
Run-off from the Lake Toba Watershed
Water used by the HEP's in Asahan River
Just for the fun of it I just mention that on November 1, 2014 the water level in Lake Toba was 52 cm lower than on November 1, 2013. On November 1, 2015 the water level was exactly the same as November 1, 2013. But on November 1, 2016 the water level was 1.60 m lower. Since November 1, 2016 the water level fluctuated a bit but is at the moment only 10 cm higher. At the moment the water level in Lake Toba is about 20 cm higher than last year. It means that we are still almost 2 m below what we like to see.
Generally speaking during the wet season it rains more often and it takes longer to bring the rain down. In the dry season the number of days that it rains is less but the rain showers, many times combined with ‘a sound and light show’, can be much heavier. The heaviest shower I recorded was almost 150 mm in two hours.
Again generally speaking it hardly rains in the morning, which is normally quite sunny, but you may expect rain in the late afternoon, early evening which normally does not last more than 1 or 2 hours. On average again we have 4 days in the year that it just drizzles all day. This can happen on any day in the year.
THE EFFECT at HORAS FAMILY HOME.
The extremely low water level of Lake Toba affected the operation of Horas Family Home in the following ways:
We had suspended our Speedboat trips as our speedboat was landed on dry land
As the water depth in the lake just in front of Horas Family Home, at the sun deck, was about 50 cm we advised our guests not to use our diving board.
We did grow kangkung where once was my favorite fishing spot
We still managed to keep some 20 cm of water in our fishing pond but we had to reduce the fish population drastically
We were growing paddy at the place where we normally moored our speedboat
As result of the more than 700 mm of rain during the last two months of the dry season, 2018, the water level of the Lake is coming up nicely and I am currently preparing my fishing rods hoping and expecting that I can re-install myself at my favorite fishing sport within a couple of weeks.
Today, November 11, 2019 the water level in the Lake is exactly the same as last year. So we hope and expect that the water level will be rising steadily in the coming months.
HORAS !!! HORAS !!! HORAS !!!
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