Forests generally use more water than grass and rain-fed crops. I doubt urban forestry can help much in water quantity. In deed, in many cases, storm flow and total annual flow volume from urbanized watersheds is higher than fully forested ones, especially during dormant seasons, simply because trees use a lot of water. Under an arid environment, planting more trees can get things worse. Grasses or sparse shrubs will be best for urban forestry that help infiltration and reduce erosion, but save water from ET - biological pumps.

Plantation in Urban areas might reduce ground water content for some time but such plantation in arid zone change the climate a lot (though very slowly). After some period, say, 25 years the aridity of the zone will be over and even rainfall in the zone may increase. Plants, trees, do consume water from below but at the same time fetch water from sky above. Grass and shrubs consume less but do not have impact on climate. Air pollution is removed by trees and not by shrubs effectively.

There are many misconceptions about the true hydrologic functions of forests worldwide.

Pls share scientific papers that show plantation forests 'fetch' large amount of water from the sky and alter climate in arid regions. There is no doubt that trees are helpful for air pollution control, but not for water quantity in dry regions. Planting trees in the wrong places or planting the wrong trees can be consequential. I attached a paper here.

One more paper to show urbanized watershed hydrology vs fully forested watersheds. Forested watersheds reduce flow volumes.

Ge sun, I agree with you partly. But regarding long range vision what I say is true.

Mukund, I appreciate if you can point me to any papers or empirical evidence that have documented the large climatic effects of planting trees in an urban region.

I am curious about the regional effects since this is important for urban forestry, reforestation or forest conservation efforts. Nothing wrong with urban forestry, but we need to be realistic for their benefits in short term and long term.

Ge sun and Mukund, there are visual effects in the Kolhapur (a typical growing city western maharashtra,) India that plantation carried out has improved the green cover in the area, had an impact on micro climate and also improved the water levels in the area. along with plantation cct and percolation tanks were built to recharge ground water. effects were visible in 8-9 years. but this region is not arid region. but in many places in maharashtra with arid climate such experiments are done and those are successful.

Nilisha, can you cite specific examples or papers regarding the Maharashtra aird climate cases? I would be interested to contrast these with the context of Los Angeles.

Interesting. it would be a different story to add percolation tanks to recharge overland flow to groundwater. Those tanks do not consume water.

Richard I will definitely look for the papers and let you know

Ge Sun You may also look for Continuous Contour Trenching (CCT) which will help in recharging of ground water table

Richard see the article in journal on water shade management in arid region of maharasthra

http://www.cleanindiajournal.com/collective_water_management_through_water_banks/

Article on watershed management

Interesting article and real story of water management, Nilisha. Thanks. For an area with precip of 500 mm/yr., to save water for people not for the ecosystems or downstreams, the water bank approach is very useful. My study suggests any quality forest plantations need at least 500 mm of water per year to survive. No wonder the plantations in the story died in a drought year. Yes, every drop of water is precious in a dry region. The wind break functions of trees to reduce downward evaporation forces are also interesting. Thanks again for sharing.

Thanks for the paper and article Nilisha, very inspiring solutions. Agreed the evaporation reduction measures are beneficial on several levels. Definitely food for thought.

Richard Please contact Dr G Singh, Scientist F at Arid Forest Research Institute Jodhpur, India for his experiments conducted with different types of rainwater harvesting structures and related plant growth there in arid conditions. His email ID is [email protected]

Thanks Pradeep, I've sent an email to Dr. Singh so I hope to hear from him soon. Much appreciated!

The only way out for water security is to have LAKES, PONDS & OPEN WELLS. We should depend least on ground water. Recharging water under ground should be replaced by collection and storing water on surface. Recharged water is required to be pumped up again taxing the energy.