[lucideer]

One thing that I rarely see mentioned when tree-planting is suggested is species, biodiversity, and impact of selection of trees to be planted on the environment.

1 tree is not equivalent to 1 tree of a different species.

Reports such as this one[0] hint to the impact of tree choice on things like human health, but I'm curious about the effects it has on climate in general (and sustainabiilty of tree populations: disease resistance, etc.).

[0] https://news.ycombinator.com/item?id=19835537

[vijayr02]

The first few tree planting drives in Tamil Nadu (a southern state of India; it's capital Chennai recently ran out of water) got significant public backlash [0] for this reason: they planted nothing but Acacia trees (due to their short growth term) and the leaves took a long time to degrade, killing all the undergrowth and creating a monoculture.

[0] https://www.thehindu.com/news/national/tamil-nadu/Acacia-rem...!

[heymijo]

> it's capital Chennai recently ran out of water

This casual statement made my eyes bulge. Like, what does this mean? How does it happen? Is water permanently gone? What are the ramifications?

I found a WaPo article on Chennai, which I see has about half a million more people than NYC.

> The city’s reservoirs and lakes are parched and its wells have run dry after two years of scanty rains here. Local authorities are trucking in water and desalinating seawater, but the supply is less than half the city’s basic requirement.

https://www.washingtonpost.com/world/2019/06/28/major-indian...

[heymijo]

This reminded me about Yemen. Eight years ago I read that Yemen may be the first country to run out of water. I went to check on where they are. It's not good. Drought is being compounded by conflict and politics.

I can't help but think that this is a harbinger of the future in more places than Yemen as climate change continues.

https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...

https://www.atlanticcouncil.org/blogs/menasource/an-update-o...

[wolco]

Yemen hasn't invested properly because of other pressing concerns. Yemen is a reminder of the past, Africa is a glimps of the future. It is not all terrible.

[dredmorbius]

"Running out of water" generally means that on a given day, or perhaps for a longer stretch (days, weeks, months) there is not enough water for essential needs, especially sewage, washing, and drinking, but also industrial and recreational activities.

After air itself, water is the most-used substance by humans (followed by gravel, sand, and rock -- we aren't out of the stone age yet), and the quantities and quality (purity) used are great enough that simple stockpiling does not generally work.

Chennai particularly is in the north-eastern monsoon belt with a wet-and-dry tropical climate (Köppen). Monthly rainfall averages vary by a factor of 100, from as low as 3mm per month in the dry season (Jan-May) to over 400mm in the wet (Jul-Dec, especially Oct-Dec). The climate chart at Wikipedia shows this:

https://en.wikipedia.org/wiki/Chennai

There are no rivers. The water table sits at 2m depth typically. And yes, it is recharged by the monsoon. The shortages are critical, but temporary.

With such an all-or-nothing weather cycle, the need is to both shed and drainnwater during the monsoon and to retain it during the dry season. That's a difficult order.

Current forecast is for rain every day.

[vijayr02]

Covered on HN as well:

https://news.ycombinator.com/item?id=20254416

[heymijo]

Thanks vijayr. I missed that one.

[vijayr02]

You're welcome heymijo :)

[monktastic1]

And 20 more Indian cities are expected to run dry by next year: https://www.firstpost.com/tech/science/indias-water-crisis-b...

[mariushn]

This approach considers biodiversity & self-sustainability: https://fellowsblog.ted.com/how-to-grow-a-forest-really-real...

[true_tuna]

It’s also important to choose local species. Planting a non-native tree species causes unexpected problems long term. See the eucalyptus problem in California.