Water Woes: Urban Flooding

"Climate change is a story about water. Too much, too little, at the wrong time." - Jesse Scott

In an earlier post, I mentioned how the frequency of extreme heat and extreme precipitation events will likely be the hallmark of climate change. Recently, I've been talking about the benefit of green roofs and shading on the urban heat island. Now I would like to speak to extreme precipitation.



Flooding in Accra, Ghana this past June left over 150 dead. This number comes 
from both those who drowned and the who died in a petrol station fire that
was offering shelter. Source: Africa News Today

One of the most devastating results of extreme precipitation is the flooding that comes with it. In some developing African countries, floodplains are home to the most vulnerable poor due to the affordability the come with dangerous lands. These floods are not just caused by sea-level rise. Floods that are the result of backed up drainage and pave surfaces are becoming more common. As temperatures rise so does the maximum water vapor content in  the area allowing to heavier rains than previously possible.

Current adaptation strategies in these areas include weighing down possessions with bricks and sitting on the highest dresser with your family until flood levels recede. This is unacceptable in the 21st century. Communities need, at the bare minimum, (improved) drainage systems and waste disposal services, to prevent the drainage from getting backed up. I will not be covering the logistics of hooking these areas up to local disposal services. Instead, I will focus on sustainable drainage systems proposed for London that may help worldwide.

Defforestation vs Afforestation: Conflicting Solutions

A clear difference in albedo between forests and croplands. Source: usagi-hikari9

Difference in surface temperature (^oC) in
 2150 with deforestation at a A)Global,
B)Linear sum of the regional, C)Boreal,
D)Temperate, E)Tropical scale compared
to current projection. Source: Bala et al.

Trees play an important role in the carbon cycle by removing CO₂ from the atmosphere. They have a regional passive cooling effect through evapotranspiration. But their albedo is lower than most other surfaces when it snows causing them to absorb more heat. This is seen an 'effective emission' of radiation because it adds to the Earth's warming. Because these qualities are at odds, both deforestation and afforestation have been proposed options in reducing climate change.

Bala et al. predict a global cooling resulting from deforestation. The used 3D climate and carbon model to simulate large-scale deforestation. The model gives more weight to CO₂ removal than similar models, so Bala et al. expect an even greater cooling than reported. The simulations were latitude based, and forest were allowed to expand in areas not currently deforested. Boreal deforestation (Map C) has the largest cooling effect with minimal increase in CO₂ levels. Tropical deforestation (Map D) causes warming, and temperate deforestation (Map E) causes minimal warming. Both show a substantial increase in CO₂ levels. The global level of net cooling seems to be linearly related to the individual regions (very similar maps for A & B).

Bala et al. do not insist on immediate total deforestation, they recognize the vital role that forests fill outside of climate control. They recommend focusing afforestation projects to the tropics. Temperate and boreal afforestation projects should be met with skepticism.

Montenegro et al.'s assessment showed cooling when there was afforestation at any latitudes. They used satellite data to create a model with 5-25 km resolution. They only looked at converting current cropland, and their albedo difference between forest and cropland was much smaller than other estimates. This showed that benefits from afforestation were not rigidly marked along latitudinal lines. Two graphs, showing the maximum and the minimum cooling as a result of afforestation so highly localized patterns. Russia, surprisingly, shows very high benefits no matter the conditions. Montenegro et al.'s model allows precise evaluation of individual projects.

Difference in net drawdown (kg/m2) for afforestation compared to current
 draw down. Minimum net drawdown conditions maximize albedo difference
between crops and forest and minimize the carbon storage of trees.
Maximum net drawdown conditions minimize albedo difference and
maximize storage. Source: Montenegro et al.

By creating a latitude based analysis Bala et al. fall into the 'wide-brush' trap described by Montenegro et al. There is the possibility that they ended up overestimating the albedo of forests because they accounted for afforestation in unsuitable areas. Montenegro et al.'s minimal conditions align best with Bala et al.'s findings, with the exception of Russia. If Bala et al. were correct concerning linear global scaling, afforestation in Russia should cool the earth despite being in the Boreal zone.



Trees in the Concrete Jungle

Urban trees are providing shade. Source: Abby Yao

I wasn't sure about talking about trees effect on the urban heat island. While planting a tree is easy enough is suburban or rural areas, in a city even a small space hard to find. And depending on your latitude trees might add to the problem because they reflect less light than snow. The planting of trees will be an important piece to the puzzle, and here's why...

Regarding CO2 emissions, trees offer a dual benefit. They take up carbon from the atmosphere by storing carbon in their wood (à la photosynthesis). Even more importantly, they prevent carbon dioxide from entering the atmosphere by keeping buildings cool. In fact, over 3 times more carbon is offset by trees' ability to limit carbon dioxide due to air conditioning than their capacity to store carbon. Much of the cooling comes from shade, but there is also ambient cooling of the atmosphere in an urban forest

Planting trees for shade not the easiest in cities where space is tight. I found one interesting solution by Shubhedu Sharma, tiny forests. I would expect most cooling to come from ambient cooling and not shade. They can help with urban cooling in at latitudes where snow albedo isn't important. However, if you are constrained by space, this project takes up more room than a tree.

At all latitude trees also offer the added benefits of reduced smog, less run-off, increased property values and improved quality of life. Tiny forests also increase biodiversity and may produce food. Reducing run-off will be especially important moving forward because more frequent extreme precipitation is expected.

Shubhendu Sharma's talk on creating tiny forests for the price of an iPod Source: TED.com

Science behind the Potwine Passive House

Source: Alexi Arango

Why does it matter?

A study in 2008 found that around 40% of the energy consumed in the US and the UK was used in our buildings. (If you look worldwide the percentage dropped to 24%, but developing countries are expected to double their contribution in the next 20 years.) Energy consumption currently accounts for 80% of humans' CO₂ contribution.
According to the same 2008 study, US and UK homes use respectively 53% and 62% of their energy on heating and cooling. Respective office buildings put 48% and 55% of their energy towards climate control.



What is passive heating?

Potwine Passive House's shining concrete floor.

Source: Alexi Arango

The concrete floor in Potwine Passive House is its 'thermal mass', a material that takes a long time to heat up and cool down. Heat moves in between the concrete and air so that it's going to the cooler of the two. In other words, when the house gets hot in the afternoon the heat is stored in the cool floor. Voilà, passive air conditioning! And at night when the house cools down, the heat stored in the concrete during the afternoon is released into the air. Ta-dah, passive heating!

Passive heating is a balancing act of evening out the warm and cold daily temperatures. Unfortunately, this means it is not advised for extreme climate temperature. (Averaging a really cold afternoon with a really, really, really cold night just leaves you really, really cold all the time.)

But why bare concrete?

After all, concrete has a lower heat capacity (how hard it is to heat and cool) than wood. The problem lays with wood's inability to conduct heat. It would cause uneven heating.

Rugs are also out. They act as insulation so that the concrete can't heat up during the day.

Potwine Passive House used blown-in fiberglass for insulation
because it was recycled and didn't need to be fireproofed.

Source: Alexi Arango 

How can insulation help?

In Erzurum, Turkey researchers found that they could get an energy savings of 27%  by optimizing insulation in ceilings, walls, and floors. They noted the inverse exponential relationship between insulation thickness and fuel/emissions reduction (i.e. eventually adding more insulation won't help keep your home comfortable). Three years later in Denizli, Turkey optimizing insulations in ceilings, walls, and floors was found to have an energy savings of  46.6% and an emission reduction of 41.53%. This is partially due to windows (which were not insulated) in Erzurum accounting for 47% of heat loss as opposed to Denizli where they only contributed 34.8%. There was no schematic of the insulation at the Erzurum site, so differences in construction technique cannot be analyzed.

While the exact amount of benefits from insulation varies, it will always help keep your home warm during the winter and cool during the increasingly probabilistic heat waves.

A Sneak Peak at Future Housing

Source: Alexi Arango

My parents went on a house tour and Amherst, Massachusetts. They came back raving about the cool the Potwine Passive House! Although, cool may be the wrong word, because even on a crisp New England morning the house was nice and toasty. This was, in part, due to the feature that stuck out to my parents, the flooring.



Source: Alexi Arango

It was a thick concrete slab, not what you'd expect on a home tour. This slab was vital to the heating and cooling of the house. It stored heat throughout the day and slowly realised it at night. In fact, 75% of the house's heating to comes from body heat and solar light. In the summer, the slab would become a heat sink. The combination of flooring and extraordinary insulation in the house keeps it comfortable year round.

This home reduces carbon emission while fluidly adapting the temperature of its environment. As the world heats up, this may be a sustainable solution for a comfortable home temperature.

 

 

COP21 Seminar Takeaways

Source: COP21

Thursday I attended Jesse Scott's talk 'The UN Climate Conference 2015: what is it trying to do and can it succeed?' hosted by UCL Department of Political Science. The UN Climate Conference 2015 also know as COP21 will take place from November 30th to December 11th in Paris, and the 196 governing bodies in attendance are there to ensure climate-related goals are being met. Scott brought both good news and bad news going into the conference.

Bad News: 

Scott mentioned that the emissions being cut would not be enough to stay below 2^oC. Nations are trying to go green while still growing their economy. Additionally, she pointed out that nations, such as the US, are slow to act because they desire national consensus. However, this may backfire because the challenge will be even larger in the future.

Good News:

Scott was "slightly more than cautiously optimistic" that COP21 will turn out better than the Copenhagen "failure". Scott pointed out significant changes in the political landscape over the past 6 years including:

• Cheaper green technology, such as solar panels.
• Investment groups and banks who see potential in renewable energy.
• Companies from all sectors, including oil, who know that climate change will prevent business as normal.
• Health experts worried about how warmer temperature will affect disease.
• Militaries who can no longer balance being combat ready and first responders for extreme weather.
• Support from people such as Pope Francis, movie stars, and You! Public opinion helps drive what politicians are willing to offer.

My Takeaways:

I am pessimistically hopeful (as odd as that sounds) that countries may be able to cut more CO₂ emissions to get closer to the 2^oC goal. However after Scott's talk I am reasonably optimistic that they will be able to sign some meaningful agreement. This is based on the number of parties, representing a whole spectrum of backgrounds, who are pressuring governments during this negotiation.

Solar Tiles: The Future Looks Sleek

The option to go solar is becoming more 
elegant. Source: Alistar King

In my last post, I mentioned my preference to solar roofs over white roofs. Luckily the option of going solar is becoming cuter! Clunky panels are no longer the only option, you can now get solar tiles that blend with your current shingles. However, curb appeal comes with a price tag. You'll need to balance aesthetics and economics.

Price comparison not including installation for solar tiles. The cost of installing solar tiles may not pay off in energy savings, but this chart does not take into account any difference in property value. Source: The Eco Experts