Making sense of the Sri Lankan Monsoon

Rainfall in Sri Lanka is not predictable and monthly averages mean very little. Although the 3 main rainy seasons start pretty much on time (give or take a fortnight) the amount of rain that falls during those seasons is variable from year to year,and in the North and East the dry season may be getting drier. So why is the monsoon so variable both from one year to the next and over longer periods?

First a little bit of simplified theory.

Surface temperature, air pressure and surface winds

things you need to know if you don’t already:

  1. rising air = low pressure: it is caused by one of three mechanisms:

a.  heating from below – convection

b.  warm ( less dense ) air rising over cooler (more dense air ) – frontal rainfall

c.  where two air masses meet or converge – convergence.

Rising air is associated with cloud formation and rainfall. (air cools, condenses – cloud and rain)

  1. descending air = high pressure, the result of:

a.  cooling from below which causes air to become heavier at the base and sink towards the surface.. or

b.  upper atmosphere convergence below the tropopause which forces the air downwards

Descending air is associated with dry conditions ( descending air heats up)

The diagram below gives a general idea of how that works. Air in a low pressure cell rises into the upper atmosphere until it reaches the boundary with the troposphere ( the tropopause) where it is prevented from rising and moves sideways. Being much colder and/ or where there is upper atmosphere convergence, the air sinks back to the surface creating a circuit if you like.

 

Fig 1

3.  Surface winds move from high pressure to low pressure

What controls the monsoon

 There are three processes at work and because they operate semi-independently of one another it makes the understanding of how the monsoon operates tricky.

  1. The Inter – Tropical Convergence Zone ( ITCZ ) and the way it moves explains the seasonal reversal of winds over the Indian Ocean basin; the change from the South West Monsoon to the North east Monsoon
  2. The ENSO Pacific Ocean events (EL Nino and La Nina) impact on the Indian Ocean by causing winds and rainfall to shift around in response to what happens in the Pacific Ocean
  3. The Indian Ocean Dipole where changes to  Sea Surface temperatures (SST’s)  also re-organise circulation patterns in the Indian Ocean

The Inter – Tropical Convergence Zone ( ITCZ )

The ITCZ is a zone of rising air (Low Pressure) located around the equator where the water (SST’s) is warmest. This is convective uplift. Rising air is associated with cloud formation and rain. At around 30 degrees of latitude either side of the ITCZ are regions of descending air. The sub-tropical high pressure belts. Surface winds blow from the high pressure belts inwards towards the ITCZ.

Fig 2. Global Circulation Patterns

Notice the don’t flow at right angles to the equator. The actually move as curved lines; north -east to south – west in the northern hemisphere, ( The North East Trade winds) and south – east to north west in the southern hemisphere (the South East Trade winds). This is due to the coriolis force; check it out here.

So why do winds migrate?

  • Remember, the SST’s control the location of the ITCZ. As the sun (which heats the ocean) moves north in the northern summer, it follows the highest SST’s will migrate north and that drags the ITCZ north.It also follows that the reverse will happen in the southern summer and the ITCZ will migrate southward.

Fig 3 The migration of the ITCZ

  • Now that is going to have an impact on the pattern of surface winds, as this simple diagram shows;

Fig. 4

and what this shows is that:

  • in January the N.E. Trades are pulled south of the Equator, deflecting to the left of their path. This is the North east Monsoon.In July the opposite occurs.
  • The S.E. Trades are pulled across the equator, and as the coriolis forces deflects the wind to the right of its path  instead of being S.E. trades they become S.W monsoon winds.

Figure 5 is a more detailed version of the process.

Fig 5

Notice the region of high pressure in the southern Indian Ocean. This is called the Mascarene High; for more try out this link. I will get back to this later in the blog.

So the migration of the ITCZ explains the seasonal reversal of wind patterns and broadly when that happens. However, it doesn’t explain why both the North East and the South West monsoons are so variable in terms of how much rain falls. That is because there are other forces at play which have a direct impact on the pattern of SST’s which in turn control surface air pressure and winds.

They are

  1. El Nino/La Nina events
  2. The Indian Ocean Dipole which has three phases; positive, negative and neutral
The influence of El Nino / La Nina on the monsoon

El Nino is a Pacific Ocean event, right? Well yes it is, but what happens in the Pacific Ocean has a knock on effect on the circulation patterns in the Indian Ocean; and it is complicated.

A.  More backgound: The Walker Circulation Pattern

The Walker circulation is an ocean-based system of air circulation that influences weather and is the result of the difference in surface pressure and temperature over the western and eastern tropical Pacific Ocean. Normally, the air over the tropical western Pacific is warm and wet with a low pressure system, (rising air) and the cool and dry eastern Pacific lie under a high pressure system (descending air).

This creates a pressure gradient and causes surface air to move east to west, from high pressure in the eastern Pacific to low pressure in the western Pacific. Higher up in the atmosphere,west-east winds move in the reverse direction to complete the circulation.

Fig 6 ENSO neutral

What you need to notice is that there is a major zone of uplift over south east Asia. Also note the area of descending air over the Middle East and the weaker uplift zone over East Africa. That helps to maintain a predominant west to east surface air flow over the Indian Ocean Basin which reinforces the monsoon.

So if you are ok with that then let’s look at how the El Nino upsets everything;

B.  ENSO events; El Nino and La Nina

El Nino is an ocean sea surface temperature event that is now pretty well understood. During El Nino events the normal Walker circulation pattern weakens, allowing warmer water to migrate eastwards towards the coast of South America. At the same time the main zone of uplift (low pressure) moves towards the central Pacific and in the western Pacific the surface airflow reverses to become west to east.

Notice now that there is descending air (high pressure) over South East Asia, and a strengthened zone of upfift over East Africa. The net effect is to establish an easterly airflow over the Indian Ocean, working against the South West Monsoon in particular.

Fig 7

So what you might expect is that in El Nino years the South West Monsoon is weaker over South Asia. This in turn can lead to reduced rainfall, and possibly, drought conditions.

La Nina is the reverse of El Nino so far as the Pacific Ocean circulation is concerned. Here the warmer water moves into the western pacific intensifying the zone of uplift over South East Asia ; the cell moves westwards effectively. Notice the zone of uplift over East Africa has gone.. bad news for those areas.. but the west to east airflow over the Indian Ocean pattern strengthens intensifying the South West Monsoon.

Fig 8

So to summarise so far: the two influences on rainfall we have looked at are

  1. The movement of the ITCZ
  2. El Nino/La Nina

It is worth noting that these events act independently of one another..

But now we have to add the third element; The Indian Ocean Dipole

C.  The Indian Ocean Dipole

 First identified in 1999, the Indian Ocean Dipole refers to spatial differences in sea surface temperature over the tropical Indian Ocean. There are three phases:

  • A neutral phase; when the SST is broadly the same across the tropical ocean basin.
  • The positive phase; this is where there is cooler than normal water in the tropical eastern Indian Ocean and warmer than normal water in the tropical western Indian Ocean.

Fig 9

Increased convection over the western Indian Ocean (warmer air rise = low pressure = rain) has a knock on effect for the monsoon; why?

ok so remember that the SW Monsoon rules in May – August; the ITCZ migrates northward and the winds blowing from the SE become south westerlies when they are dragged across the equator into the northern hemisphere. ( check out figs 3&4 ) Plus being warmer the relative humidity of the air is increased. This should mean the monsoon intensifies

  • The negative phase; this is where there is warmer than normal water in the tropical eastern Indian Ocean and cooler than normal water in the tropical western Indian Ocean.

Fig 10

Here the pattern reverses. To the west of India there is a zone of descending air which surpresses the moisture content of the surface winds and leads to lower rainfall.

 

D. Putting it all together

These three influences don’t necessarily synchronise with one another and are pretty much independent of one another as well.

Generally ENSO impacts the Indian Ocean by re-organising the atmospheric circulation but so does the Indian Ocean Dipole.

So

  • El Nino = drought
  • La Nina = enhanced monsoon
  • Positive Dipole = enhanced monsoon
  • Negative Dipole = surpressed monsoon

But as I wrote earlier.. it now gets tricky.

  1.  Don’t forget the system can also be in neutral!

2.  Not only that but the ENSO and Dipole events vary independantly, in intensity and impact.

Last point; various phases of both ENSO and the IOD can occur concurrently but at different relative strengths. Confused yet?

One example; a moderate El Nino such as occurred in 1997 should have lead to a poor monsoon over India but it didnt. this was because it was outweighed in influence by a stronger positive IOD event and in 1997/8 India received above average rainfall. This puzzled many meteorologists and led to the discovery of the IOD in 1999.

So what doe the evidence show? The following table illustrates how the different events have come together to affect the monsoon in recent years.

An IOD event can offset the impact of El Nino or La Nina although in 2004 it was El Nino that “won”.

Impact of ENSO events

 

year occurrence Impact % normal monsoon rainfall
2004 El Nino Drought 88
2005 Neutral Normal 101
2006 Neutral/positive IOD Normal 103
2007 La Nina Excess 110
2008 La Nina/negative IOD Above normal 105
2009 El Nino Severe drought 79
2010 La Nina/negative IOD Normal 100
2011 La Nina Normal 104
2012 El Nino/Positive IOD below normal 92
2013 Neutral above normal 106

 

So that’s what it comes down to.. a dynamic system driven by variations in sea surface temperature which drive atmospheric circulation patterns.

The complicating factors are that:

  • The time spans between ENSO events are not even.
  • The ENSO events vary in strength.
  • Occasionally the IOD intervenes

Looking then at all of this: It does shed some light, however, on why monsoon rainfall is highly variable and, therefore, so difficult to forecast. It also may help us to understand why South Asia is prone to periodic drought; the subject of the next article.

Footnote: Don’t forget Global Warming!!

According to Dr. Evan Weller abased at Monsah University in Australia global warming is set to complicate matters even more.

As climate changes, so sea surface temperatures will rise, but the increase won’t be even. Some regions will warm more than other regions. Over the eastern Indian Ocean, the waters to the north are predicted to warm faster than those in the south. This will have the effect of  pushing the ITCZ further north over the eastern Indian Ocean. It will also affect the SST  gradient north to south and that impacts on pressure differences and ultimately circulation patterns. The question is how will this interact with ENSO and IOD events and what effect will that have on the climate of South Asia. It may well serve to intensify the south west monsoon but there is no agreement on that at the moment. It is also possible that the location of the warmer water pool in the Indian Ocean (both positive and negative phases) may shift in location and this could also affect the local surface wind patterns. There is still much that is not understood!

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Colombo floods; getting relief to the victims

As flood waters start to recede  they have been replaced by a different flood; the flood of blame and recrimination.  A number of journalists have been quick to lay blame in several areas, including the meteorological office, the disaster management centre and the government. However, whilst journalists and politicians wasted time looking for scapegoats others got on with a much more important job; getting help and aid to the flood victims

The government would have it that the flood  was the result of all those poor people who built on marshland.  As a result they have said that they will be removing upwards of 2500 families from unauthorised sites; (see Sunday Times 12th June) This is either ignorance or political sophistry.

“The squatter families will not be offered compensation or alternative locations, Sri Lanka Land Reclamation and Development Corporation (SLRDC) Chairmnan W.M.A.S. Iddawala told the Sunday Times. He said that in a survey carried out after last month’s devastating floods, the corporation had identified the squatter families which should be evicted.” Sunday Times

While some properties may have inhibited the flow of flood water in and around the canals they did not cause the flood.

Building on marshland does not cause a flood. It might put people in harm’s way, but it doesn’t cause a flood to happen.The sheer volume of water falling on an unprotected catchment is what caused the flood.

So why the evictions? We can only guess

  • it is always convenient to have a scapegoat to divert attention away from the failings of the government and its officials
  • they will not have to pay compensation to these families
  • it is part of a broader government strategy of relocating families in unauthorised settlements into the government built apartment complexes currently springing up around the city
A vulnerable population

A good place to start is to define what vulnerable means in this context. Two aspects need to be borne in mind;

  • the immediate physical vulnerability to the danger of flood
  • the longer term vulnerability to the economic impacts of the flood

Why were so many people exposed to this devastating flood and its longer term impacts? A  number of factors contributed to render the population vulnerable;

  • The areas around Colombo are low-lying and flood prone
  • there are no effective flood defences in place to control the Kelani Ganga
  • Suburban population densities are high quite close to the main river and its tributaries

Figure-2-Population-density-in-Colombo-district

Population densities in the Colombo area source: researchgate

  • Housing density is high and many of the side lanes are narrow which would later hamper rescue and relief efforts
  • Most households are in the  lower middle to low income bracket and not able to withstand the financial impact of losses due to the flood
  • How many had adequate insurance cover? None; as one person told me; “it isn’t in the Sri Lankan culture to purchase home insurance”
Flood Impact

In all more than 150,000 people were temporarily displaced by the flood. Although relatively few homes were completely lost many have suffered water damage, small shops kades and bakehouses have lost their stocks of goods to sell, livelihoods have been wrecked, many have lost all their possessions in the flood and will find it hard t replace them.

This is Imi’s story. She lives with her mother and infirm grandparents in Welivita, part of Kaduwela to the north-east of the city. This is what the flood meant to families such as hers.

Disaster Relief

The Disaster Management Centre should have been the body to co-ordinate flood relief efforts. However, at the height of the flood it was under 2 metres of water; not ideal. They did warn of the impending flood and they did issue evacuation alerts and to be fair other measures were put in place once the flood struck:

  • 1500 military personnel were organised into 81 teams and deployed to the flood areas, as were the police
  • boats were provided to rescue trapped households from roofs and upper stories
  • safe areas were identified and evacuation centres set up
  • rescued families were transported to the evacuation sites where there were emergency rations, blankets etc

However, good as this was there doesn’t seem to have been much coordination of the relief effort.  The President did instruct the local officials the Grama Niladahri to visit all affected areas and people in their districts to get an idea of what the problems were, and who was in most need of help but according to this Sunday Times report the response was at best patchy.

and there were problems:

  • some evacuation centres were overrun and became heavily congested
  • the emergency relief packages were pitifully small and not everyone got them
  • there was a mismatch in terms of what was needed and what was given; victims urgently needed clothing, sanitary wear and medicines; they didn’t receive much of any of these
  • there were not enough boats available to rescue people
  • some houses, especially the less accessible, were never visited by the rescuers
  • calls for help made to the disaster centres went unanswered in some cases. For many help never came.

Questions have also been raised about where all the foreign aid went because it certainly didn’t reach many of the victims if newspaper reports are to be believed. This from the Sunday Times 12th June:

“Three weeks after floods ravaged many of the areas adjoining the Kelani river communities are waiting for the government machinery to move in to provide aid, rebuild houses and provide other relief. Flood victims stranded in Kelaniya, Kelanimulla and Angoda areas, this week, claimed there was no responsible officer at grassroots level to monitor the process of distributing dry rations to the destitute.”

Local Volunteers

In the vacuum left by what some see as government ineptitude local volunteer groups sprung up in different districts across the city. One such group was the Welivita volunteers. Initially they came together to help their friend Imi (see above) However, they could see the need for a wider effort and within in a short time they:

  • organised themselves into a coherent group with a steering commitee
  • created a facebook page for the group
  • visited the area to get an idea of the extent of the problem
  • went to the local Grama Niladhari (government official) to identify the families most in need
  • launched an online campaign on facebook for donations
  • put out regular bulletins on the progress of donations
  • itemised a list of essential items for relief packs and school packs; all costed out; each cost around 5000 rupees and was paid for by donations. (the value of government aid packs was 1500 rupees and wasnt necessarily what people wanted or needed)
  • collected the packs and then distributed to needy families
  • when that was done they embarked on a clean up of Imi’s house and the areas nearby

They did this in the space of two weeks: and you can check out their page Welivita Volunteers where you will get full details on what they did, how they did it and also a good selection of photos which graphically illustrate their work;

So the point about their work was that it was:

  • carefully structured and organised throughout
  • bureaucracy was kept at a minimum
  • targeted at those in most need
  • delivered quickly and without fuss into the hands of the needy
  • not expensive
Comment

After the 2004 Tsunami the people were told that in future the government would be ready; those scenes of chaos in 2004 could not happen again..that does not seem to be the case. Looking through recent newspaper articles it would seem that the government effort raises more questions than answers;

  1. Where did all the emergency aid go? Many complain that they have not seen any of it.
  2. Journalists slate the government for complacency and inactivity
  3. Why was the Disaster Management Centre located in a flood prone area? It is worth noting that millions of rupees worth of telecommunications equipment stored at the DMC has also been ruined in the flood
  4. Where was the co-ordination necessary to mount a coherent disaster management plan.. indeed where was the plan?

After events like this one governments all over the world (certainly in the UK) drone on about lessons to be learned.. evidence is that those lessons are rarely learned. However, there are some take away points:

  1. Maybe it is time to look at flood prevention especially in the upper Kelani basin. It will be expensive in the short run but will save in the longer term. Have a look at flood prevention schemes on the Los Angeles and San Gabriel rivers, in Los Angeles, USA for an example. flood retention dams in the upper course, flood spreading zomes in the lower course, channel improvements, engineering of the channel of the kelaqni, raising the river banks.. these could all be looked at.
  2. By all means give people alternatives to living in marshy areas and on the banks of the Kelani, but these should be viable alternatives and in consultation with those living in those areas.
  3. A proper disaster management contingency plan for flooding needs to be in place. Military personnel need to be trained. Boats need to be available.
  4. There needs to be someone of ministerial rank in charge of flood relief; clearly the DMC is not up to the job.
  5. There needs to be some recognition that  roles need to be specialised.

There are two stages to a flood event like this:

Initially the need is for search and rescue; the military are best placed to do this; I suspect that if they had been in charge the rescue operation would have been properly coordinated and way more efficient. They have the helicopters to overfly flooded areas and provide first hand intelligence to direct the rescue effort plus they have a command network that would be effective in these situations

  • Once rescue is underway the focus is on relief and the government could learn a great deal from the work of the local volunteers; how they organised themselves, targeted relief on those in greatest need, paid heed to what the victims needed and so on.
  • They might also consider how they might utilise the power of social media to better direct their efforts.
  • They could think of building on the huge amount of good will shown by local people to the victims by setting up local part time or volunteer flood relief groups who could be trained as a first line of the relief effort and mobilised at times of flood.

One thing is for sure; the river will flood again whether people are living on marshland or not. The question as ever, is will the government be ready?

Colombo Floods 2016

The South West Monsoon  hit Sri Lanka hard in 2016. The heavy rains have resulted in landslides in Kegalle and flooding in Colombo  for example, which have displaced more than 300,000 across the island with at least 58 left dead and a further 130 missing. 
Now in 2017 the monsoon season has been accompanied by large scale flooding and mudslides which have left 202 dead and 600,000 people displaced. The areas around Rathnapura and Kalutara have been badly affected but, Matara in the south of the island has also suffered serious flooding. In all the floods and landslides have destroyed 1,735 houses and damaged 9,432 while 146 schools were also damaged –
Predictably, for some it all turns out to be the government’s fault; but it isn’t.

Climate change in South Asia is a reality and one of the outcomes is that rainfall will become less predictable and the frequency of extreme rainfall events is set to increase. Sri Lanka needs to brace itself for more events like this, and do you know what? In the short run there isn’t much anyone can do about it.

The 2016 flood; what happened?

May is statistically the start of the South West Monsoon in Sri Lanka and brings rain to the South and West of the country.

As any A level geographer will tell you  (putting it simply);  the South West monsoon season is the result of a seasonal reversal in wind direction, from North East ( off the landmass) to South West (off the ocean)

This year the Indian sub-continent ( and also Sri Lanka) has been suffering big time from heatwaves which have seen the temperatures soar above 40 deg C. for weeks on end. High land temperatures vis-a-vis the ocean, create an air pressure imbalance; lower air pressure over the land higher over the ocean, an creates an airflow from the Indian Ocean on to the land masses of Sri Lanka and India. The bigger the difference in temperature and air pressure between the two the stronger the inflow of air towards the continent. Warm wet air rising over the landmass = rain.

Figure3

typical SWM situation; credit: one data.edu

But this year the monsoon has arrived with a vengeance

Why the heavy rain?

So we already have a set up whereby the winds are coming from the South-West.. from the warm ocean surface. However, you have to factor in a low pressure system that formed in the Indian Ocean to the East of the island and developed into a tropical storm which has moved northwards towards India. As it developed it set up a strong inflow of “wet” air coming off the Indian Ocean and the Island land mass forced that wet air upwards, leading to torrential rain. So this is just a sketch to give the reader an idea of what is going on, where the winds are coming from.

IMG_0833

 

image_1463542469-f07ac6cb02

satellite image of the depression

so the depression is the white blob of cloud north of Sri Lanka.It is now moving North -East. What you have to imagine is that the air flow is inward/upward and anti-clockwise reaching way back into the western Indian Ocean; those thicker cloud elements suggest more rain to come!

A note on depressions for the uninitiated

a low pressure system or depression creates an inflow of air in a broadly anti-clockwise spiral. Warm air heated from below rises.. the warmer the air the faster and higher it rises. As it rises it cools, condenses and produces cloud and rain.

4857328

here we are interested in the diagram on the right; credit the britishgeographer

The Indian Ocean this time of year is warm in any case; but I read that the surface ocean temperature may be around 31deg C. which is way above where it should be, and that is only likely to make things worse.

Nb; This isn’t a local effect however as some seem to think, but related to global circulation patterns

So in this case very warm moist air spirals upwards. As air condenses to form water droplets it releases heat back into the rising air.. it fuels more uplift.. clouds reach up higher into the atmosphere resulting in the formation of cumulus clouds stretching high up towards the tropopause. As a rule of thumb the stronger the uplift the lower the air pressure and with it the stronger the inflow of surface winds at the base of the depression.

The net result; torrential rainfall, strong winds and violent thunderstorms.

Flooding in Colombo

According to some, the construction of the large lakes such as the Diyawanna lakes and the improvements to the canals and drainage systems was supposed to mean that Colombo would not suffer any more from floods like the 2011 flood. Maybe this was wishful thinking, however.

Colombo district will always be vulnerable to flash flooding because:

  • large areas are low lying; no more than 5 metres above sea
  • the land gradient is slight so water has nowhere to drain away
  • large areas are urbanised which reduces infiltration, and exacerbates surface flow
  • Rivers like the Kelani river flow off the west flanks of the central highlands which have been receiving high levels of precipitation. That flood water is eventually going to end up on the lowland. Colombo sits on the natural flood plain of the Kelani Ganga and the river does periodically what rivers do.. it floods especially when it is choked with sediment washing done from the central uplands.

srilanka-map

  • on top of this heavy rainfall and intense thunderstorms are common occurrences in the Colombo district

This does seem to be an extreme event, however. Over 300mm of rain fell right across the catshment, both in the upper and lower reaches ( as much as could be expected in a month)  Intense rainfall on to an urban surface had nowhere to go.

The Kelani Hydrograph

a hydrograph plots the way rivers react to an intense rainfall event. I found this one which is taken from the 2005 flood. What you can see is that the river reacts quite quickly to rainfall events.. less than 24 hours it seems:

kelani hydrograph

Points to note:

    • very steep rising limb
    • short time lag from peak rainfall to peak discharge
    • high volume of peak flow
    • gentle falling limb; flow is still high3 days later

If you study the Kelani valley in the hills where it rises you can see why it will flood downstream

Dhammika Heenpalla creative commons

credit: Dhammika Heenpalla

  • the valley is steep sided which would accelerate rainfall into the channel as surface flow and throughflow
  • the slopes are long and locally rainfall is high so a large amount of rainfall will end up in the channel very quickly
  • there is no flood plain for flood water to spread over
  • so all the floodwater is penned up in the valley unable to escape; instead thundering down to the lowland plains to the west.
Impact

It’s too early to assess the damage caused by the landslides and flooding across the island. What we do know is that over 200 families are missing  with 58 pronounced dead following landslides in the central uplands that engulfed 3 villages.

Across the island upwards of 300,000 people have been rendered temporarily homeless. The cost in terms of damage to property will become clearer as time passes. In the meantime a huge relief operation is swinging into place with the Sri Lankan armed forces at the forefront of rescue and relief efforts.

Who will be shouldering the cost?

  • More than likely the lower middle and low income groups whose homes have been engulfed or inundated.
  • In Colombo, those living in unofficial shelters next to the Kelani river, those in the low lying suburbs around Colombo;

and it is just worth thinking about what it means for a family to see their home flooded, their possessions ruined; and in the main these are families who cannot easily bear the cost of putting there home back together

Imi's housec3a63a24f545cd193e22afeebf0a38bb

My friend Imi’s house; this is the reality of flooding: putting her mother’s house back together will take way more money than they have; life is set to be difficult for sometime to come and what you need to do is multiply that by 300,000 to get an idea of what this means for a small island like Sri Lanka

We might “study” this as a hazard event BUT let’s also remember that this is very much a human tragedy.

For some stark video footage check out http://www.sundaytimes.lk  the online page and scroll down the front page to the video links.

Last thought

As with the UK a couple of years ago, when we get an extreme weather event it is almost “de rigeur” to blame the authorities for not anticipating the event and protecting against it. It seems it always has to be someone’s fault. The same appears to be happening in Sri Lanka. I saw a Sunday Times.lk  opinion piece asking; ‘why is this happening again?” Well unfortunately that is nature for you. What did people expect? That the government could simply tell the rain to go away?

Point is that we live in an increasingly hazardous world which we do not control and cannot always predict. If we choose to live in areas which can become vulnerable to hazards such as flooding and landslides we need to accept that when these extreme events occur we are at risk. That doesn’t mean that efforts should not be made to moderate the impact of these events

Given that the outcome of climate change may well mean an increase in extreme weather events (among other things) a question that might be asked is what is being done to moderate the impacts of future events

  • The meteorological department based in Colombo is already on the case; a great deal of research is already underway on a range of issue related to weather and climate and is well worth checking out: try this out: http://www.meteo.gov.lk/index.php?option=com_content&view=article&id=47&Itemid=200&lang=en
  • But the met office need access to much more powerful computing power and technology if the aim is to improve the forecasts
  • So knowledge is the first step but then it comes down to what the government intend to do with that knowledge. The danger could be that in the rush for economic development planning for an increasingly hazardous environment may not be a high priority.. that would be a mistake.

So what might need to be done.

  1. Seems to me  understanding where the flood water comes from is a starting point. Does the Kelani River need for its banks to be raised higher?
  2. Is there a need for engineering solutions to control/impound water in the central highlands in the event of high rainfall as for instance the Los Angeles river in southern California so that Western Province is less at risk?
  3. Can anything be done to increase the flow of floodwater from drains and canals to the sea?
  4. In the highlands is it time to re-forest the slopes of the hills to stabilise them and reduce the landslide hazard? Should geological surveys be undertaken to identify and map areas of high vulnerability
  5. Should people be moved away from dangerous locations?

All basic stuff isn’t it but that’s where the thinking needs to go; its an old saying but prevention is much better than a cure and in the long run less expensive.

The point is that this type of extreme event will happen again and again; all the predictions point in that direction. What the government needs to do now is put in place a coherent disaster management plan, with a senior minister at the helm to co-ordinate rescue and recovery and possibly to take control away from ineffective and self seeking officials and politicians who have shown that they are not up to the task.

In the follow on article i will be looking at  the relief effort, the declaration of flood areas as high security zones  and what can be done to help mitigate against future floods.

Just published; have a look also at this from CEPA

http://groundviews.org/2016/05/19/sri-lanka-floods-2016-avoiding-the-mistakes-of-2004/?platform=hootsuite

 

 

Waldringfield UK; a community led flood protection project

In 2013 a storm surge in the North Sea threatened communities up and down the East coast of the UK. Whilst many coastal settlements had benefited from flood protection schemes others like Waldringfield, a small village on the Deben estuary in Suffolk were left out of the loop and vulnerable. So when the surge came the inevitable result was flooding to the village.

Despite the flood there were no plans to put flood protection in place. Instead of taking a fatalistic view, however, the local community came together to raise the funds to create, not only an effective flood protection scheme (one of the first of its kind in the UK),  but at the same time create a nature reserve to enhance the local area. This case study is the story of how this project developed.

What is a storm surge?

Storms along the coast can cause sea levels to rise way above their normal level which leads to coastal flooding. So what causes a storm surge? The two diagrams taken from the UK Meteorological  Office site explain how this can happen.

  • A deep low pressure cell (depression) moves eastwards into the North Sea basin.
  • The low pressure at the centre of the storm “pulls” the water level up, by about 1 cm for every 1 millibar change in pressure.

europe - detailed

source: UK meteorological office

  • As the depression moves down the North Sea basin it generates high winds from a northerly direction. The winds push the sea water southwards and towards the coast, causing it to “pile up” along the coast, raising the sea level and creating a “surge”. This is a predictable event. The residents in Waldringfield knew 24 hours in advance that the surge was on its way, for example.
  • The strong winds in the storm generate large waves on top of the surge which can cause damage to sea defences, or spill over the top of sea walls adding to the flood risk.

europe - detailed

source: UK meteorological office

Introducing Waldringfield

Waldringfield is a small village on the west bank of the river Deben in Suffolk, on the East coast of the United Kingdom. The village comprises 225 houses with a population of 464 (2012). The village has a village hall, pub, boatyard and is home to Waldringfield Yacht Club.

The maps below show the location of Waldringfield in Suffolk and in the UK


                                                                                      waldringfieldlocation east coast

The 2013 Flood

On the 5 December, 2013 a large storm surge hit the east coast of the UK causing widespread flooding along the coast. This was a prime example of low pressure, high winds and high tidal conditions combining to create surge conditions;

  • It was the largest tidal surge since 1953 and water levels were actually higher than in 1953
  • Many East coast estuaries were flooded; The Stour, Deben and Orwell rivers all reported  flood damage.

Waldringfield is on the Deben estuary and suffered significant flooding on the river frontage. The following is the list of damage:

  • The river wall to the north of the village was overtopped, causing flooding of the meadow behind it.
  • The boatyard and about 18 residences on the Quay were also flooded to a depth of about 5 feet,  as well as several beach huts and land to the south of the village.
  • There was one casualty, who was taken to hospital by ambulance.
  • The fire service attended to a fire around 1.30am, which was caused by the flood water shorting the electric gates of a property on the Quay.
  • A heating oil tank and a gas tank floated off it stand, but, fortunately, remained attached to it feed pipes
  • The river wall was badly damaged in places, but it wasn’t breached.

The total cost of the damage and repairs was estimated to be: £10 million overall

The Waldringfield Flood Defence Group (WFDG)

The group got together informally 6 months prior to the flood. They were aware of the flood risk plus they were also aware that Waldringfield was not included in existing flood protection schemes for the Deben estuary. This was possibly because only 18 properties and the boat yard were at risk of flood at that time. (even though the real estate value of those properties is possibly above £20 million

Note: The village of Waldringfield  stretches about 1km inland from the river Deben and the majority of the village sits well above flood level. The lane known as The Quay is the  area liable most likely to flood in the village, see map below:

Waldringfield map cropped Page 1

When the flood occurred, and with no direct help from the government forthcoming, the 18 affected  households formed The Waldringfield Flood Defence Group (WFDG). It had significant support from a number of sources including: The Environment Agency, Suffolk Coastal District Council. The Deben Estuary Partnership, Waldringfield Parish Council, Lord Deben, Chairman of the UK’s Independent Committee on Climate Change, and the local MP, Dr Therese Coffey. Very quickly the group came up with a plan to create a two stage project for the immediate area area: this involved:

  1.  an outline plan for the design of new flood defences; including a raised sea wall 1km in length, flood gates, and movable flood barriers to protect the boatyard (completed within 3 months)
  2. the protection and preservation of a freshwater meadow and marshland habitat north of the village through the repair and strengthening of the river wall.
  3. restoration of  salt marsh which would add to the protection the sea wall.

Funding for the  £1million project was achieved mainly through grants,  including £633,000 from the Government’s Coastal Community Fund. The initial work on the salt marsh  was partly funded by the Suffolk Coast & Heaths Area of Outstanding Beauty unit.), and is visible at low tide.  A further 1,000m of protection is being funded by the Coastal Communities fund at a cost of £100,000

How do salt marshes protect flood defences?

Salt marshes play a major role in flood defence.  Salt marshes are effective buffers to wave action, by creating shallow water which reduces the power of waves. The wider the salt marsh the the more effective it is in protecting the sea wall. One study carried out at Cambridge University found that “salt marshes can reduce the height of damaging waves in storm surge conditions by close to 20%”

What has been achieved?

Stage 1: Raising the flood defences: protecting homes, businesses and jobs.

The live link will take you to the project page which details each step in the process. Stage 1 was completed in February 2015. The main points are as follows:

  • A new reinforced wall was built in front of the properties on The Quay at 3.5m OD. Each of the riverside properties now has its own steel reinforced gate to allow access to the footpath

DSC_0064

  • A  steel flood barrier was erected next to the boatyard. This can be closed by the Environment Agency in the event of a flood warning.
  • Removable steel barriers have been erected in the boatyard; they will be removed to allow boats  access to the river for launching but can be put in place in the event of a flood warning. (see below)

closable flood barrier removable flood barrier

Stage 2: Raising the river wall: repairing a footpath and creating a freshwater wildlife reserve

The live link will take you to the project page which details each step in the process. Stage 2 was completed in October 2015.

The main object of the scheme has been to create a wildlife reserve on a freshwater marsh area, which was formerly owned by the local vicar. When he died his executors agreed to allow the conversion of part of the farmland to a lagoon and nature reserve.

The lagoon area at present is bare.. it looks like a building site.. but it has been planted with sedges and within a few years it will naturalise to form an attractive habitat for birds and mammals, such as the water vole and a family of otters.

lagoon

see small scale map for location

After the flood there was concern over state of sea wall to north of village and the footpath which was also damaged when flood water overtopped the wall. So a decision was made to flatten the top of the wall and to widen the footpath.

The footpath is now much wider and more level as the photo below shows. Some locals probably feel that it is unnatural but access has been improved, and the path is accessible and usable all year. Access to the nature reserve will also be improved for locals and visitors alike.

footpath

the footpath looking north; now wider and flatter

Salt marsh restoration

The saltmarsh in front of the sea wall to the north of the village varies in width. Immediately north of the village it is quite degraded; see below but widens out . The WFDG scheme allows for the installation of brushwood  fences which have been installed in the marsh in front of the sea wall. The hope is that these fences will trap sediment on the outgoing tide and help to build up the marsh in front of the sea wall to add some degree of additional protection to the sea wall and the footpath. There remains another 1000 metres of fencing to install to complete the job.

degraded marsh

the degraded salt marsh

brushwood fences

brushwood fences in place to protect the sea wall

Local community action: is this the way forward?

This scheme is the first of its kind so far as I can tell and The Environment Agency is keen to use this project as a pilot to demonstrate how local communities projects such as this one can be the forerunner for other schemes which fall outside of government support.

  1.  The WFDG were successful because:
  • they were already organized
  • they had the necessary skills to produce a fully drawn up and costed project plan
  • they had the skills to lobby for financial support
  • they acted quickly
  • they worked together and without internal wrangling/disagreement

2.  The value of the community based approach was that they designed it themselves and so it was fit for their purpose; basically they got what they wanted but also created a scheme with significant utility and value to the village as a whole.

3.  At the same time they turned it into a multi purpose project by:

  • protecting the sea wall
  • creating a much more accessible and usable footpath alongside the river, an improved amenity for all
  • working with the estate of the recently deceased vicar to create the wildlife reserve which will be of broad ecological value but also will provide a real amenity to be enjoyed by locals and visitors and will add to the attractiveness of the riverside

I recently interviewed Janette Brown, the secretary of the Waldringfield Flood Defence Group and started by asking her to take us back to the night of the flood. You can listen to the full interview here: