Rain and storm for Cpt

[access]

We had some late season rain in August, so many areas are now superficially green. The rain did not soak into the soil, nor run off significantly into the rivers and dams. 6 weeks rain is not enough to last a whole summer.

ah ok, only drove through that area recently, havent been there in years.

also its been a while since we've had a week of just rain in the cape, I cannot actually remember the last time it rained for the entire week.

Historically, winter precipitation in the SW-Cape has been fairly reliable (as predictable as the summer South Easterly winds).

We may be part of Africa geographically, but our weather patterns are dependent on mid-lattitude extra-tropical cyclones (otherwise known as cold-fronts). Just saying...

indeed. looking at development around the cape peninsula, its booming. vegetation destroyed for massive housing developments. old houses demolished and replaced with apartment blocks, 1 family on the property turns into 10 or 15 families on the same space of land. I saw a water demand chart the other day, I cant understand how the graph kind of levelled out and didn't continue climbing with all the development and massive population influx(just look at the traffic) in the cape.

so much more people and to think IF a drought happens it would hit exponentially harder.

 

[Nerfherder]

its amazing how lush and green it is around voelvlei dam in riebeek/tulbach valley, water puddles and varkblomme all over. strange to think that the dam levels are so low.


more like underdeveloped water system than a "drought" it seems sometimes. did not keep up with development and now blame the weather?

Its the lowest rainfall in recorded history.... yes its a "drought"

 

[Hosehead]

We are not too dissimilar from California with regards to drought and climate change.
Back in the 90s when I studied there the northern state winters were much like our own normal winters
But unlike us California has since recognised that they are suspectible to prolonged years long droughts
And have started to manage it from lessons learned https://www.newsdeeply.com/water/co...lature-can-prove-drought-lessons-were-learned

 

[greg_SA]

We are not too dissimilar from California with regards to drought and climate change.
Back in the 90s when I studied there the northern state winters were much like our own normal winters
But unlike us California has since recognised that they are susceptible to prolonged years long droughts
And have started to manage it from lessons learned https://www.newsdeeply.com/water/co...lature-can-prove-drought-lessons-were-learned

To me it sounds like they also had to experience a drought before they learned... So its sounds just like us

From the article:

We saw first-hand that in most cases conserving water and being more efficient offer the cheapest and fastest way to deal with water scarcity. By comparison, building entirely new supplies, whether through desalinization plants or surface water storage, is much more expensive.

And it looks like during the droughts, they also relied on demand management, just like CoCT.

The bills are only being passed in California now...

That being said, in SA, the whole country is relying on old infrastructure that is not being maintained or improved adequately Big institutions (governments / municipalities) are slow to learn...

 

[Icemanbrfc]

Next chance for rain in the catchment areas of the main dams is next Monday, Tuesday.

Low rainfall but at least something.

Damn, we need more

 

[Geoff.D]

Looks like the rainfall is going to be quite high in the western cape mountains , as high as 40 mm in some places.

 

[Gordon_R]

Looks like the rainfall is going to be quite high in the wester cape mountains , as high as 40 mm in some places.

Models are still rather fickle, but I'm not seeing numbers that high. This looks like a relatively fast moving front, with limited moisture, and brief duration of orographic enhancement.

My guess would be 5-15mm at sea-level, with 20-30mm possible over the mountains. Only a small fraction of that will find its way into the catchments (mainly Berg River dam, which has benefited most this winter).

 

[Geoff.D]

Models are still rather fickle, but I'm not seeing numbers that high. This looks like a relatively fast moving front, with limited moisture, and brief duration of orographic enhancement.

My guess would be 5-15mm at sea-level, with 20-30mm possible over the mountains. Only a small fraction of that will find its way into the catchments (mainly Berg River dam, which has benefited most this winter).

Yesterday 50.8 mm was measured at the Dwarsberg weather station in the Jonkershoek mountains. So this last front now past did cause a fair amount of rain in the main catchment areas. Pity the front moved so quickly though.

Constantiaberg had 11 mm and the Cederberg weather station measured about 16 mm.

Time to dust off the Gauteng rainfall thread . We had our first rather insignificant shower (6 mm) BUT the lightning was something else!

 

[Rouxenator]

All the water from Jonkershoek flows straight down Eersterivier, gets raw sewage from Stellenbosch added and then makes it's way to the Macassar sewage plant where it flows into False bay.

 

[Gordon_R]

Yesterday 50.8 mm was measured at the Dwarsberg weather station in the Jonkershoek mountains. So this last front now past did cause a fair amount of rain in the main catchment areas. Pity the front moved so quickly though.

Some of the runoff from peaks near Dwarsberg flows into other dam catchments (Berg River and Theewaterskloof), but overall it was a low rainfall event.

Edit: It has been rather cold, with light snow over the mountains yesterday. Doesn't feel like Spring!?

The next cold-front will be on Tues 4th and Wed 5th, but again the rainfall figures are uncertain (and unlikely to be very significant).

 

[Mila]

So no significant rain for you guys this year.
Can we now establish that global warming ****ed you guys over and this is now what the weather is going to be like?
Or are we still hoping its just a temporary thing?

 

[Gordon_R]

So no significant rain for you guys this year.
Can we now establish that global warming ****ed you guys over and this is now what the weather is going to be like?
Or are we still hoping its just a temporary thing?

1. Rainfall has always been fickle, on a scale of days, months, and decades.
2. The winter of 2017 has been exceptionally dry (although cold), but one data point doesn't make a trend.
3. It is inherently more difficult to link climate change to rainfall variability, rather than temperature which is much easier to link.
4. The SW-Cape is surrounded by ocean, which somewhat tempers major changes in weather, compared to the Northern Hemisphere.
5. Projected long-term climate impacts on the SW-Cape are likely to be felt between 2030-50, so it is probably too soon to tell.

 

[nightjar]

So no significant rain for you guys this year.
Can we now establish that global warming ****ed you guys over and this is now what the weather is going to be like?
Or are we still hoping its just a temporary thing?

Thirteen thousand years ago a big part of the earth was covered by ice and I would guess that global warming has a tiny bit to do with the fact that a lot of the planet is ice free today.

What happens in the next ten thousand years is not my worry and, with modern technology, humans are likely to survive.

 

[Geoff.D]

Prospects look good for today and part of tomorrow.
The dam level increase last week was only 0.1% overall. The trend as plotted in the CT pdf file seems destined to continue.

 

[Gordon_R]

Prospects look good for today and part of tomorrow.
The dam level increase last week was only 0.1% overall. The trend as plotted in the CT pdf file seems destined to continue.

14mm overnight here in Kenilworth.

45mm recorded at SAEON Dwarsberg. This is a proxy for Berg River dam inflow, which should increase by around 1%. Other dams not so much, so the overall trend is already downwards...

 

[Geoff.D]

What is quite interesting is the "joining up of two low pressure systems", one extending down the west coast of Africa, with the weather front pushed up from the south, leading to the extension of the front that is supposed to even reach us here in Gauteng tomorrow.

All due to the high pressure area in the South Atlantic ridging in behind the weather front for a change. Pity this did not happen earlier in the winter season.

 

[Geoff.D]

So I looked into a paper I remembered about the 1981 Laingsburg flood. Will post a link if I find a link.

That paper analysed when most of our rainfall occurs and what sort of systems are associated with rainfall.
If I remember correctly the analysis showed that cut off lows that combine with low pressure systems coming down from the tropics driven by high pressure ridges can cause very large rainfalls in very short times. These systems normally happen from August to November. So is this current system over the country an example?

 

[genetic]

Prospects look good for today and part of tomorrow.
The dam level increase last week was only 0.1% overall. The trend as plotted in the CT pdf file seems destined to continue.

Prospects good? There wasn't much at all.

 

[Geoff.D]

Prospects good? There wasn't much at all.

45 mm in the jonkershoek mountains is significant.
Not to talk about what the country is likely to get out of the current system.

 

[genetic]

45 mm in the jonkershoek mountains is significant.
Not to talk about what the country is likely to get out of the current system.

Which is not the catchment for the City of Cape Town's water supply. Rest of the country getting rain is great, but doesn't help us unfortunately.