This is one season, so
unpredictable that explains the heightened media interest in the monsoon
progress. Much has been hyped of the monsoon onset, coming 4 days later than normal.
And yet, yesterday, when the monsoon covered the entire country, 4 days earlier
than normal, media coverage in contrast had been fairly muted.
As seen in the IMD graph,
accumulated rainfall till yesterday noon may appear at first glance near normal”. The actual data presents a
more sobering picture. As on yesterday noon, monsoon deficiency stood at a
whopping 23%. Such a figure is worrisome, as on one hand key reservoirs across
the nation have not received adequate water as considered comfortable. On the
other hand, the extremely poor rains in Karnataka and Central Maharashtra can
adversely affect the production of coarse grains.
But if you think this a massive
deficiency, then consider this. Less
than a week ago, the rainfall deficiency was nearly 50% of average. In a span
of just 6 days, the deficiency was cut almost in half. Combine this feat with
the fact that monsoon covered the entire country, 4 days earlier than normal
and how does the glass now look? You can take your pick. Revival or Mirage?
The unpredictability of
weather or climate is so enormous that it really takes the really brave to
stick their necks out to venture a prediction. Weather or climate after all is basically
chaotic non-linear systems which mean much of their behaviour is through “random walks”. Dr Andy Edmonds in an incisive article entitled “The Chaos theoretic
argument that undermines Climate Change modelling” in the blog WUWT observed:
“So, what does it mean to say that a system can behave seemingly
randomly? Surely if a system starts to behave randomly the laws of cause and
effect are broken?
Chaotic systems are not entirely unpredictable, as something truly
random would be. They exhibit diminishing predictability as they move forward
in time, and this diminishment is caused by greater and greater computational
requirements to calculate the next set of predictions....prediction accuracy
will drop off rapidly the further you try to predict into the future.
Lorenz estimated that the global weather exhibited a Lyapunov exponent
equivalent to one bit of information every 4 days. This is an average over time
and the world’s surface. There are times and places where weather is much more
chaotic, as anyone who lives in England can testify.
this means though, is that if you can predict tomorrows weather with an
accuracy of 1 degree C, then your best prediction of the weather on average 5
days hence will be +/- 2 degrees, 9 days hence +/-4 degrees and 13 days hence
+/- 8 degrees, so to all intents and purposes after 9-10 days your predictions
will be useless.
course, if you can predict tomorrow’s weather to +/- 0.1 degree, then the
growth in errors is slowed, but since they grow exponentially, it won’t be many
days till they become useless again.”
Put simply, the
uncertainties accompanying forecasting elections or share market movements pale
into insignificance as compared to forecasting weather, particularly so, the
monsoons, which remains one the most difficult weather phenomena to predict. This doesn’t mean that chaotic systems like
the monsoon cannot be predicted at all. All it means is that they could be
forecasted reasonably accurately at very short time frames and the longer the
timeframe, the more inaccurate that they can get.
The only way then
to forecast monsoons is then by following a dynamic rather than a linear approach
viz. as physical conditions change, the forecast changes. This is why the IMD
downgraded their June forecast from what they made in May. So did this blog. We
slightly modified our June forecast from the first we made in May. As compared
to the IMD June forecast of 96% LPA (101-91% of LPA) ours continue to stand at
95% (98-92% of LPA).
To read our monsoon
forecast Click here
So what has changed since June?
The El Niño
critical indices have not only crossed threshold values but intensifying
rapidly so much so an El Niño maybe unofficially declared by this month end. The
being +0.7 deg C and SOI at -10.6. Officially, they
can declare an El Niño event only after September end as these indices values
need to be maintained for at least 3 months.
How would an El
Niño impact the current monsoon? LS Rathore, chief of IMD even
yesterday, still ruled out any effect. We totally agree
with the IMD’s assessment. Each El Niño is different so is the current one. How
different? Rajesh Kapadia who
administers the blog Vagaries of Weather and I decided to team up to write a
joint post to be published later this week or sometime next week why we think
that the El Nino, even if confirmed, can be expected to only marginally affect
the monsoon, if at all.
Ocean Dipole (IOD) within ENSO (El Niño/La Niña) neutral conditions usually can
become a wild card. In May the IOD was weakly negative. In June, many
international models indicate it becoming moderately positive. Early this
month, the same models suggest a return to neutral mode with a weakly positive
bias. Accordingly, there appears no problem with the IOD messing up the monsoon
however some confusion about the Madden Julian Oscillation
(MJO) another critical variable as different models gives contradictory
forecasts. My friend Rajesh Kapadia blogged: “MJO "holding on" till 22nd July.” Rajesh is a much more seasoned forecaster with plenty of experience than I do and certainly he has meteorology running through his veins. I however depend on the CPC-NCEP-US model which
suggests favourable values till 3rd week end and progressively
expected to weaken from then, though not any way unfavourable for the monsoon. Based on my assessment, the
MJO is likely not to create any unfavourable conditions till month end, if
lucky till mid August.
On the whole, all elements
of the monsoon system are at last in place which is why we had very good
rainfall last week. Whether it stays that way till September is very difficult
to tell but our forecast remains hopeful.
A top IMD official used the
analogy of cricket to aptly describe the current monsoon’s progress. He said
that we are in the middle (July-August) overs with the openers (June) out
cheaply. July-August rains account for 65% of the South West Monsoon rains and absolutely
critical for agriculture to avoid failure. Considering the fact that we have a 23%
deficiency to offset, from the third week of July to August mid, we need some very
big hitting to maintain the required run rate. How this critical period pans
out is anyone’s guess. However, the 3rd week July looks extremely promising as
if we are very likely to experience the best rains till now for the current
season. A couple of sixes and who knows -we maybe down to single digit deficit
by July end? And of course August is yet another story, all monsoon forecasters
will be keeping their fingers crossed.
We expect Central parts of
the country, the Northern plains to get very good rains next week starting from
this week end. We also expect the rainfall activity to increase over peninsular
India with a huge chunk of peninsula India’s deficiency to be made up, This
though will not succeed to eliminate the deficiency altogether, as now being
experienced in peninsular India.
A red alert: Very heavy
& widespread rains forecasted from tomorrow for entire North Central and
N-E states which means really bad news for Assam Flood rehabilitation
To read our
monsoon forecast Click here
absolutely Rajan..we are meteorologists, not magicians ! MJO views differ Rajan, not that I am right, but somehow, they tend to change every few days..something unheard of for MJO..ReplyDelete
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