Simply there is not a simple answer! you need to dig into details first. This phenomena is highly nonlinear and many uncertain factors are involved. I am puzzled with so called "Experts" who judge and declare their final opinion before analyzing the event/data. You have to see and delve into a comprehensive detailed 2D-1D, coupled pressurized-free surface, hydraulic-hydrology model which has to build by:

1- The rainfall event

2- Design rainfall of the underground culvert and gutters of the street (basically detail-design and report of drainage system)

3- Land coverage of upstream watershed in a high resolution raster

4- Sub-watershed delineation details

5- Detailed high resolution DEM

6- Soil infiltration raster

7- The geometry of inlets of culverts and grates of the DI (maybe the event was an "inlet controlled" not "capacity controlled" incident)

8- Possibility of reduction of capacity based on the clogging.

9- ...

Any claim before computation without the above-mentioned is an "INVALID" and just throwing a rock in the dark!

I still do not know Shiraz IDF and the event's return period. So if the return period is 500 Yr. Then such a flash flood is not fault of designer or anybody. Unfortunately, I have seen frustrated people try to find a victim and blame him/her/it for the flood they still do not have enough information on it.

Many opportunist flood experts, try to hypothetically make a fortune and make themselves visible with known but not related and accurate information, quotes such as:

- Whenever you change the land coverage you increase the chance of flood!

(Okay Einstein!, every Tom, Dick and Harry know that! you are only an attention whore.); Try to find information, then the rest is just building a full model of the event and then the answer is easy to find.

Simply there is not a simple answer! you need to dig into details first. This phenomena is highly nonlinear and many uncertain factors are involved. I am puzzled with so called "Experts" who judge and declare their final opinion before analyzing the event/data. You have to see and delve into a comprehensive detailed 2D-1D, coupled pressurized-free surface, hydraulic-hydrology model which has to build by:

1- The rainfall event

2- Design rainfall of the underground culvert and gutters of the street (basically detail-design and report of drainage system)

3- Land coverage of upstream watershed in a high resolution raster

4- Sub-watershed delineation details

5- Detailed high resolution DEM

6- Soil infiltration raster

7- The geometry of inlets of culverts and grates of the DI (maybe the event was an "inlet controlled" not "capacity controlled" incident)

8- Possibility of reduction of capacity based on the clogging.

9- ...

Any claim before computation without the above-mentioned is an "INVALID" and just throwing a rock in the dark!

I still do not know Shiraz IDF and the event's return period. So if the return period is 500 Yr. Then such a flash flood is not fault of designer or anybody. Unfortunately, I have seen frustrated people try to find a victim and blame him/her/it for the flood they still do not have enough information on it.

Many opportunist flood experts, try to hypothetically make a fortune and make themselves visible with known but not related and accurate information, quotes such as:

- Whenever you change the land coverage you increase the chance of flood!

(Okay Einstein!, every Tom, Dick and Harry know that! you are only an attention whore.); Try to find information, then the rest is just building a full model of the event and then the answer is easy to find.

I think it is a consequence of the so-called global warming of the planet, as it causes, among others, torrential rains in a short time, which causes the soil not to reach to capture the water by infiltration, which results in landslides and avalanches, and also it does not allow the underground layers to be filled.

If global warming warms the planet, then huge ocean surfaces should stastically warm up too, such that in the first moment the total evapo-transpiration flux into the atmosphere of the planet increases. But this buffers the temperature increase of any surface (including those of green plants; also ocean surfaces cool that way and lead to vertical convective heat, salt and nutrient exchange with deeper ocean layers - which again buffers the latter effect).

Things are complex so that possibly Kaveh Zamani is correct: a very detailed model, integrated into a broader system, needs to be elaborated and tested against data to identify the (statistically relevant!) cause-effect relations. The ECMWF model system is a nice model structure possibly applicable (as a strucuture) to your region, too.

This is true, we must not prejudge the causes of floods before doing a study. But these studies must be prepared in advance to identify areas at risk of flooding and make risk maps to avoid the resulting damage.

Not much impact.

Please have a look at this useful RG link.

Article The future of extreme climate in Iran

The hydrological situation in Iran traditionally oscillates between extreme droughts and floods caused by changing patterns of circulation during the transition from winter to spring. Recently, the delicate balance between these two opposing regimes has been disturbed and the amplitude of the oscillations has clearly increased. This fact is also confirmed by the computer simulations.

The impact of climatic factors is further strengthened by changes in the surface drainage system; according to some sources, they were very important in the case of recent floods.

https://www.atlanticcouncil.org/blogs/iransource/nowruz-floods-in-iran-anger-many-but-reasons-are-complex

The answer to this question can’t be complete without an appropriate synoptic analysis. An in-depth study will take time, but at this moment, it is clear that main synoptic feature causing such a flood was the doubly split jet stream with the reconnection point located over Iran. This particular form of a jet stream has been formed by two persistent high pressure blocking systems. The first was located over the Atlantic Ocean and the second over the European part of Russia.

I was positively surprised to find an excellent synoptic analysis supported by the animated maps and satellite images at BBC website:

https://www.bbc.com/weather/features/47725850

The interactions of the Pakistan-Arabia Dust Cloud is being canceled out by the increased moisture created by Global Warming. See http://www.ecoseeds.com/cool.html and especially http://www.ecoseeds.com/cool2.html

The increase in the atmospheric moisture is countering the effects of the last 5,000 years of the atmospheric Dust Cloud effects that was created when grazing animals were domesticated ate everything to dust, in the Middle East, especially from what is now the "Emprty Quarter" of Arabia.

And when the Indus Valley civilization chopped down all of the Pseudomonas-host plants (that create the rainfall--see Discover magazine http://discovermagazine.com/2012/apr/07-does-rain-come-from-life-in-the-clouds ) then, that canceled out the regular summer monsoonal rainfall from the Thar desert of India westward to Morocco.

So to mitigate the effects, everyone in India and everywhere westward to Morocco, needs to buy some flood insurance right now, especially if their homes are at the bottom of wadis.

And instead of looking at these floods as a problem, start the revegetation of wadis and their banks and revegetate the drainages leading to the wadis, so instead of causing flash floods, the water can seep into the ground, and start recharging the ground water.

And in the cities, the cities will need to rethink their stormwater management designs, so that there are are methods to dissipate the excess water, for example produce flood-fields like we do for the Sacramento River at the Yolo Bypass, before it can cause floods.

The Yolo Bypass is a wide swath of land that is owned by the government that is farmed, but with the provision that at any time, that land would be used to divert the excess flow of the river if necessary.

HERE are my four favorite websites, that may help answer your question, and also help you follow the progress of the rain cloud moisture and Pakistan-Arabia Dust Cloud interactions on a daily basis, and provide some basis to make predictions. Without including the Dust Cloud daily interactions as part of every India-to-Arabia weather model, it is impossible to predict floods and droughts properly---

1.) https://www.nrlmry.navy.mil/shared-bin/display_image.cgi?URL=/aerosol_web/globaer/ops_01/india/current.gif - This is where the daily atmospheric dust is tracked, down to 20 micrograms per cubic meter, and you will see that as low as 40-80 micrograms can change the track of Category-5 cyclones, or stall the flow of moisture to create floods, like it does frequently in India, and is today.

2.) http://tropic.ssec.wisc.edu/real-time/imagemain.php?&basin=indian&sat=m5&prod=irn - Then, overlay the Dust Cloud image over the rain cloud SSEC raincloud Infrared NHC Enhancement from Meteosat-7 and watch their interactions that way.

3.) http://rammb.cira.colostate.edu/products/tc_realtime/index.asp - Then when you want to see the world championship battle between the Pakistan-Arabia Dust Cloud and the Indian Ocean and Arabian Sea cyclones, look at the RAMMB archives under Indian Ocean. The pick a cyclone, and do down to the "Storm Relative 16 km Geostationary Water Vapor Imagery" archive, and then on the last date, click on "Loop" and watch the scary, horror movie. The dust cloud is the red--orange entity, and the center of the cyclone has a little red cyclone ikon.

4.) http://www.ecoseeds.com/art3.html - When I discovered this fantastic Dust Cloud-cyclone interaction, I included this titanic battle in my Environmental Artwork series, showing 10 different interactions of the Dust Cloud with different cyclones, as paintings No. 48, and 52-60.

5.) On Research Gate, I have posted many questions if you do a search for "questions" about the Pakistan-Arabia Dust Cloud, plus the issue of the Pseudomonas bacteria forming the summer rainclouds for the India to Arabia region.

Attached is today's Dust Cloud image plus the SSEC rain clouds

I agree that there is no simple answer to a specific extreme precipitation event. In China, if you analyze each heavy precipitation, they are different in details. I also think that to understand this sad event happened in Iran, we need to analyze in different levels. First is synoptic level: which system dominate this precipitation event. Then is the climate level, which position is this event in the historical precipitation during the same period, is there significant trend? At last, we can ask which factor (e.g., global warming, deforestation, ...) should be responsible for the event. About flood, I think flood is not easy to avoid if heavy enough precipitation fall in a short period. But we may look in detail what kind of role other factors play in the flood disaster, which may give us experience to reduce disaster as much as possible in the future.

That is what I think about this sad event.

Actually there is at least two relatively "simple" answers to droughts and floods from China westward across the Middle East and North Africa--1.) What are the atmospheric Dust Clouds doing today to modify the rainfall patterns?

And 2.) Who is burning down the tropical forests today, where the rainfall for the planet originates with the Pseudomonas bacteria living on those native tree leaves?

See the daily horror two-frame cartoon at https://www.nrlmry.navy.mil/shared-bin/display_image.cgi?URL=/aerosol_web/globaer/ops_01/mongolia/current.gif'

Unfortunately, China is caught between those two activities--the Dust Clouds forming to your north and northeast which will move the deserts eastward until the north of China will become uninhabitable. And in SE Asia, where the tropical forests are being converted into palm oil plantations, and are on fire today, where the raincloud for the southern half of China originate?

Where will over one billion people living now in China, migrate to in the future, when the Dust Clouds to the north and east converge with the lack of rainfall from the chopped down forests from the south? That was the problem faced by the Indus Valley people 3,500 years ago, when they chopped down all of their Pseudomonas-host trees to fire the bricks for their 1,000 cities--the rain stopped, and they abandoned every one of those 1,000 cities, and those areas not reoccupied for 1,000 years?

You can watch this week, as the Cyclone Fani, instead of making landfall in the middle of India, is getting pushed by the wall of the Pakistan-Arabia Dust Cloud at 120 degrees off track towards the NE, to smack right in the center of Bangladesh. You can see from comparing the daily NAAPS dust cloud images with the storm track, that it only takes 20-40 micrograms of atmospheric dust per cubic meter, to make a tropical cyclone change its path?

If you visit the Colorado State RAMMB-CIRA tropical storm website, and go to the FANI page, and then view the loops in the archive for the "Storm Relative 16 km Geostationary Water Vapor Imagery" at http://rammb.cira.colostate.edu/products/tc_realtime/archive.asp?product=16kmgwvp&storm_identifier=IO012019 you can clearly see the interaction of the Pakistan-Arabia Dust Cloud and the cyclone--The Dust Cloud is pushing Fani like a orange-brown hand NE, directly towards Bangladesh, whereas without the Dust-Hand, Fani would have followed a directly westward track along the 15 degree latitude line across Indian, and then probably rained on Arabia also.

The people of Bangladesh are going to suffer, just because the people of Arabia let all of their camels and sheep and goats eat the native vegetation on their Peninsula, that created bare soil, that then got the dust airborne in the first place.

Later on this month, after Fani causes whatever damages and deaths, should Bangladesh be able to sue Arabia for "Environmental Negligence" for the damages that the cyclone will cause, when the domesticated-animal-created Arabian dust forced Fani to change its track? Who let the sheep out that flooded Bangladesh? That would be a very interesting question for the insurance companies of Bangladesh and their lawyers?

This is the "Butterfly Effect" being seen for real--a grazing sheep eating a native grass plant to the ground in Arabia, can alter the track of a tropical cyclone and flood Bangladesh and kill hundreds of people and destroy the homes of thousands to tens of thousands?

This is a beautiful picture Craig Carlton Dremann , which clearly shows the positions of dust cloud and tropical storm. I also believe that cyclones and dust cloud interact with each other over Indian Ocean, as they are so close to each other and dust can affect energy balance. Dust cloud can affect cyclones and cyclones can also affect dust cloud. In the picture, the cyclone's structure seems still round and complete and the dust cloud becomes a long narrow band. Is it possible that the cyclone pushes the dust cloud westward?

Dear Shuyun,

Thanks for your your answer. When you are doing your studies of anthropomorphic atmospheric aerosols, you need to add "atmospheric dust" into your models as an additional man-made aerosols, because most of the northern hemisphere deserts have been man-made by over grazing and plowing marginal and arid rainfall areas.

Also, the atmospheric dust is a more powerful climate modifier, even more powerful than any Category-5 cyclone. And, the atmospheric scientists need to give a name to each Dust Cloud, so we can start discussing these interactions?

If you go back to http://rammb.cira.colostate.edu/products/tc_realtime/archive.asp?product=16kmgwvp&storm_identifier=IO012019 and click on the loops for cyclone Fani, you will see that the Pakistan-Arabia Dust cloud is moving eastward out of Arabia, and forms a continual wall blocking the cyclone from moving westward across India.

So, FANI, instead of moving westward along the 15 degree of latitude as it was on April 30, the leading edge of FANI started encountering the Dust Cloud the next day, and the Dust Cloud kicked FANI out of its westward track, 130 degrees to the northeast towards Bangladesh.

Also, if you click on any of the "Archive" seasons, then go to any of the "North Indian Ocean" cyclones, like 2017, and MORA at http://rammb.cira.colostate.edu/products/tc_realtime/loop.asp?product=16kmgwvp&storm_identifier=IO022017&starting_image=2017IO02_16KMGWVP_201705272100.GIF&ending_image=2017IO02_16KMGWVP_201705301210.GIF and see the Dust Cloud interaction with the cyclones when you watch the loops for the Storm Relative 16 km Geostationary Water Vapor Imagery - Archive

Your give rise to interesting questions related to climate change about the recent floods that hit Iran recently. However, to understand the broad impact and scale of the floods, other factors must also be taken into account such as the mismanagement – before, during and after – of the floods by the Iranian authorities. Indeed, Iran has faced a severe drought during a decade and has been hit by floods suddenly. Local, regional and national authorities were unprepared to this. Infrastructures such as canals and ponds, which were supposed to collect excess of water, suffered from a lack of maintenance and were thus unable to fulfill their purpose. Riverbanks also suffered from a lack of maintenance. Public personal, which tried to bring assistance to the population hit, was untrained and underequipped to face the problem properly. Also, political rivalry between the different levels of power within Iran hampered the public management of the floods and so the means – already insufficient – have not been used in the best way.

Everyone can watch today the interaction between the Cyclone Vatu, that should be headed straight to make landfall in Iran today, and how what I call the "Pakistan-Arabian Dust Cloud" is keeping it bottled up in the Bay of Bengal, where it will quickly dissipate there.

Now the interesting side-effect, is that all that moisture will completely miss Iran, plus it will delay the arrival of the regular monsoon moisture to Bengal.

You can see in the images from https://www.nrlmry.navy.mil/shared-bin/display_image.cgi?URL=/aerosol_web/globaer/ops_01/india/current.gif and

http://rammb.cira.colostate.edu/products/tc_realtime/archive.asp?product=16kmgwvp&storm_identifier=IO022019 --view the interaction of the Dust Cloud and the Cyclone every 3 hours.

And the battle really begins when the cyclone gets a slight advantage on the Dust Cloud, and starts making small break in its leading surface which is normally very smooth and even, starting at 2019-06-12 at 09:00Z, close up of that battle line attached.

The cyclone VAYU has now been caught by the Dust Cloud like a Venus Fly Trap leaf, and the Dust Cloud is in the process of "digesting" the moisture, and wringing it out over a particular spot in the ocean. That exact same event happened with Cyclone GONU was trapped in the Straits of Hormuz, and then when it was killed, some of the moisture was flung toward Iran during Gonu's last gasp during its final death. See http://www.ecoseeds.com/GONU3.html

So if the Dust Cloud trapping occurs over land, instead of over the ocean, that is when the moisture is wrung out of the cyclone over land, and causes floods over India, Pakistan, Arabia, Iran, etc.

Every climatologist and monsoon researcher between Arabia and India need to start adding the effects of the "Pakistan-Arabia Dust Cloud" to their models, and let's give this entity a name, so we can discuss it, because it is a more powerful weather modifier, more powerful than the most powerful cyclones on the planet--it directs them, changes their directions, causes floods and droughts, interferes with the monsoons, traps cyclones and ultimately eats those cyclones for lunch and dinner.

Today, Cyclone Vatu is still being held offshore by the Pakistan-Arabia Dust Cloud, since for a few days now, has been trying to move towards Iran and produce some rainfall for the native plants trying to survive in the Plateau.

But the domesticated animals keep eating the native vegetation to the dust, creating constant dust storms that stop the moisture from coming.

Also, you create a "heat island effect" when you remove the soil-insulating layer, when you strip off the native perennial grass vegetation in Arabia, Pakistan, Iran, Iraq, Syria, Afghanistan, Turkey, etc. on a country-wide massive scale---Whereas, if you had left only 4-5 cm. of vegetation left to cover the soil, that could lower the daytime air temp. by as much as 20 deg. F. or from 38 deg C. down to 30 deg. C.

Think of insulation in a home, we need to keep the native plant insulation on the land, to lower the effects of global warming, on a local scale, and to keep the soil from becoming airborne to further weaken the rain clouds trying to fix our man-made deserts?

See soil temp. measurements from the Mojave desert at http://www.ecoseeds.com/cool.html

So, each desert nation situated between 10 deg. and 40 deg north latitude, should set aside a large portion of the annual defense spending, and use it to start defending their populations against the "Dust Clouds" and start fighting the "Heat Island" effect that is being created by the stripping of the insulating vegetation off of their countries grazed areas.

Setting aside those areas as "Ecological Restoration Preserves" and get rid of all of the domesticated grazing animals, and hire all of the graziers to restore the native grasslands that their flocks destroyed.

If we do not start doing this right now, then large parts of the planet between 10 and 40 degrees latitude, where over a billion people live right now, just like for the Indus Valley civilization many centuries ago, can become uninhabitable.

So all of the money spent annually on defense by each of their countries to guard against human enemies, will prove to be a total waste of funds, when there will be nothing left to defend when the ecologies of these countries become uninhabitable for their people and for their enemies alike.

That is exactly what happened when the Indus Valley people abandoned their 1,000 cities, those 1,000 cities sites were not reoccupied for 1,000 years.

Replanting the native plants could unite us against our common enemy--the Dust Clouds. And the native plants could insulating and conserve the soils for us.

All of the arid and desert countries between 10 deg and 40 deg north latitude, we need to get rid of 90% of our armies and stop buying weapons from the weapon-merchants, and acknowledge that we have different religions but we can accept diversity on this tiny planet?

Because we have a much bigger foe to fight, and the only thing that matters for our future survival, is to unite against the Dust Clouds and start the process of native plant revegetation right now?

That means China ($250 bil.) and Saudi Arabia ($68 bil.) and India ($67 bil.) and Israel ($22 bil.) and Oman ($12 bil.) and Pakistan ($3.5 bil.) isn't it a bit of a paradox, the countries who have the biggest problems with the Dust Cloud decertifying their countries, and are on the front lines of losing that battle?

And this countries are among those that are spending the most money on their militaries, thinking they need to spend any money to protect themselves from some human enemies--when the real enemy is the destruction of the ecosystems around them, and allowing the Dust Clouds to take over?

Watch today, as the Pakistan-Arabia Dust Cloud, call on support to keep the cyclone from bring rain to Iran today, by getting the Egyptian Dust Cloud to lend some dust to the fight, image attached. And look at the massive heat-island effect the lack of vegetation causes in North Africa?

The Research gate spell checker changed my paragraph--Should read--

That means China ($250 bil.) and Saudi Arabia ($68 bil.) and India ($67 bil.) and Israel ($22 bil.) and Oman ($12 bil.) and Pakistan ($3.5 bil.) isn't it a bit of a paradox, the countries who have the biggest problems with the Dust Cloud desertifying their countries, and are on the front lines of losing that battle, are among those spending the most on their militaries?

If you watch the movie of the battle between the Cyclone Vayu and the Pakistan-Arabia Dust Cloud, and as usual, the Dust Cloud won, keeping the cyclone bottled up offshore.

Plus, the Dust Cloud has continual support and renewed supplies of dust from the Egyptian Dust Cloud, but the cyclone did not have the support of the monsoon moisture from the east, so gave up today, and spread across the Arabian peninsula. Watch the movie at http://rammb.cira.colostate.edu/products/tc_realtime/loop.asp?product=16kmgwvp&storm_identifier=IO022019&starting_image=2019IO02_16KMGWVP_201906101515.GIF&ending_image=2019IO02_16KMGWVP_201906162115.GIF

What is happening in Iran is also happening in parts of North America in recent years. Besides the dust clouds, there are also high-humidity, low-level "clouds" which are not reported in the weather channels here. They can bring rain when the weather report says "clear skies"!

Too many changes are happening too quickly. Basically there is more evaporation from the warmer ocean, so we should expect more rain and more floods and get prepared for it.

The high humidity with low level clouds can be caused by at least two conditions-

1.) Presence of the dust cloud, moisture is going over, but the Dust Cloud keeps the moisture from forming rain clouds, by changing the dew point.

2.) The lack of Pseudomonas host plants--the rain clouds general form best wherever there are still Pseudomonas host plants in the area.

For example, the place where it rains regularly in summer in Arabia is the tiny stretch of mountains above Salalah in Oman, image attached--you would not believe you are in Arabia? See http://www.ecoseeds.com/salalah.html

Also see -- http://discovermagazine.com/2012/apr/07-does-rain-come-from-life-in-the-clouds

Dear Michael Issigonis

I’m puzzled by your observation:

“Besides the dust clouds, there are also high-humidity, low-level "clouds" which are not reported in the weather channels here. They can bring rain when the weather report says "clear skies"!”

Do you ascertain the systematic error in our numerical weather prediction models?

Attached is today's water vapor image from http://tropic.ssec.wisc.edu/real-time/imagemain.php?&basin=indian&prod=wv&sat=m5

What you will see is about the same amount of water vapor over southwestern Arabia and all across central Africa, but where are rain clouds forming?

Right on top of the Pseudomonas host plants in Africa, and not in Arabia, even though there is about the same amount of water vapor going over both.

And then on the west coast of India, you can see the Pseudomonas host plants also producing clouds, where they still grow in the Western Ghats.

You could have moisture, or high humidity or low level clouds moving over you, but without the Pseudomonas host plants in the area, always have a hot, dusty desert?

Not until you start replanting the native Pseudomonas host plants, and keep the land vegetated, so that the Dust Clouds will not form, the moisture will stay in the air and never cool your hot desert down, with beautiful rainfall.