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 <div class="title"><h3>5.32 -Morning Dew Collection on Terrace Walls to Mitigate Climate Change </h3><br><h3 class="ch-owner">Karleigh Litt, University of Guelph, Canada </h3></div>
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<p>Suggested citation for this chapter.</p>
<p> Litt,K. (2022) Morning Dew Collection on Terrace Walls to Mitigate Climate Change , In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org</p>
       <h3 class="title-bg">Background: Regions Where Terrace Wall Collection Would be Useful</h3>
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          <p>It is estimated that there are 300 million people globally that rely on terrace farming (Kidron 2000).  Tens of millions of smallholder terrace farmers are located in the dry subtropics, and they are increasingly susceptible to droughts associated with climate change (Chapagain and Raizada, 2017). An innovation that can combat climate change is a terrace wall dew collection system scaled for smallholder subsistence farmers. Farmers can place a low-cost polytetrafluoroethylene lining sheet on terrace walls that will collect atmospheric vapor and transform it into a potable liquid form for boiling (Takena, 2003). Farmers can also use the more low-labor approach of placing slow growing crops directly against the wall for the condensate to seep into the soil (Chapagain and Raizada, 2017). The target regions for this innovation have an extended dry season and lack of rainfall, increasing chances of drought, like East Africa, Yemen, Central America, Nepal, and India. This innovation will be a low-labor and low-cost alternative source of water for subsistence farmers, livestock and slow growing crops on terraces.</p>
<p>The occurrence of dew collection relies on a few different factors, first of which is capitalizing on fog, uphill nearby locations, and daily temperature. Morning dew is a natural process that happens through the formation of water vapor as the hot daytime temperatures cool down at night – which is typical in drylands and desert environments. Wind speed, air pressure and humidity are factors that create the formation of morning dew. When the maximum vapor pressure is reached in the atmosphere from the temperature transition, the air become full of water molecules that will connect with a hydrophobic surface to create a liquid (Josh and Paini, 2010).</p> 
 	<p>Dew formation is dependent on the amount of humidity in the air. If temperatures remain relatively constant, times of the day when dew formation occurs can be predicted. Examined through the climates of distinct habitats in the Negev Highlands of Israel, clear mornings had collected greater amounts of morning dew, rather than windy and cloudy mornings (Josh and Paini, 2010). Continuous condensation in this climate creates continuous dew formation from sundown to after sunrise. Paired with the north and west facing habitats blocked form high winds, and the hilltop location of Negev, demonstrated an ideal climate and location for a terrace wall morning collection system.</p>
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       <h3 class="title-bg">Operation of the Terrace Wall Dew Collection System: Synthetic sheets or rock alternatives </h3>
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<p>It is important to undertake this practice in locations with cool nights and humidity which are needed for dew formation (Jin and Wang, 2017). Once a location is found close to the subsistence farmer, the next step is to introduce a collection surface. According to the Journal of Hydrology, an ideal material for dew collection would be a sheet of polytetrafluoroethylene foil, which is a low-cost hydrophobic material to which water does not adhere but rather beads and drips down (Takenanka, 2003). The challenge is obtaining this material. The sheets can be bought from the international online retail site, Alibaba.com, costing $14.40 US dollars per 24 rolls of 25 square feet. The polytetrafluoroethylene foil is easily mouldable and ideal for shaping on the terraces, but they are recommended to be protected against harsh weather. Due to the lack of durability of the sheets they will need to be replaced often if experiencing high winds and sand. This particular hydrophobic surface would bring in higher yield of water short term but suffer from long term damage that can be costly to a subsistence farmer. These materials would not be the easily accessible for subsistence farmers without the help of an aid or government organization.</p> 
<p>An easily accessible and efficient alternative to a hydrophobic surface on a terrace wall are porous rocks (Agnoletti, 2012). Rocks have a natural hydrophobic surface, aside from a small initial absorption of the first wetting. The concept of dew collection from porous rocks has been traditionally practiced on the island of Pantelleria, a volcanic island in the Mediterranean (Agnoletti, 2012). The volcanic presence on the island creates a large access to porous, stone materials for terrace walls which increases the surface area and crevices for dew collection. Many terrace walls around the world are already reinforced using rocks, so the only innovation here is to switch to more porous rocks.</p>
<p>Once the landscapes are established, the smallholder farmer can proceed to place crops on the steps of the terrace against the walls for overnight dew formation. If the plants are planted so that the soil is directly against the hydrophobic surface, the liquid vapor will trickle into the soil and provide water for those plants (Agnoletti, 2012). In terms of collecting the morning dew from the hydrophobic surfaces, the farmer should plant the crops such as slow growing fruit trees directly against the terrace wall so the dew is directly beneficial. Creating a trench in the soil closer to the wall could potentially promote collection of the dew water as it drips. Therefore, the labor involved with this system diminishes greatly once the initial setup is complete. The terrace wall dew collection system essentially creates a low labor irrigation system for plants that thrive in large dew forming conditions for moist soil, an ideal concept for a hot and dry subtropical climate endangered with drought.</p>
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       <h3 class="title-bg">Steps to Guide a Subsistence Farmer </h3>
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<p>1.	The small-scale farmer will locate terrace walls which already drip water from dew.
<p>2.	Then they will use the hydrophobic surface chosen and line the terrace walls. Stacking porous stones or propping up foil. 
<p>3.	If the farmer chooses to gather the dew themselves, the sheets should be left overnight, and dew is expected to form 30 minutes before sunrise. This method would require the collection of dew from the surface before the sun rises. The alternative would be to plant the crops/plants directly against the hydrophobic surface so the dew can run down into the soil directly.<p>
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       <h3 class="title-bg">Benefits of Combining Dew Collection with Annual Himalayan Plants</h3>
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<p>There are large numbers of terrace farmers in the Himalayas. The subtropical Himalayas presents heavy dew formation from the months of October to February, resulting in plants that have adapted to the lengthy periods of dew they are used to growing in (Josh and Paini, 2010). Large amounts of exposure to dew formation can negatively affect a plant’s transpiration rates, photosynthetic rates, and efficient use of water. Local plants derived from the Himalayan regions would be ideal to combine with terrace dew collection systems. For example, the perennial plant Optiva, a small tree that can be used for wood and fuel, reacts well to high dew forming growing conditions. It stands out as having a small reduction in photosynthetic rate and transpiration rate (Josh and Paini, 2010). As well as being a high fibre plant for fuel, Optiva is highly digestible and makes a preferred feed for livestock. This would be a substantial resource for subsistence farmers, because they can use it for cooking, heating, feeding, and resale for family income. This Himalayan plant represents an opportunity on cool mountains and hillsides to effectively use the collection of morning dew (Pant et al, 2018). Similarly adapted plants may exist in other mountainous regions of the world.</p> 
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       <h3 class="title-bg">Helpful Links to Get Started </h3>
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<p>The materials needed for this terrace wall system can be purchased on international trade websites Alibaba.com: https://www.alibaba.com/product-detail/Pure-tin-foil-ptfe-reusable-non_62204925724.html?spm=a2700.galleryofferlist.0.0.78b9617eMQsJnN&s=p
  and Indiamart.com: https://www.indiamart.com/proddetail/aluminum-foil-tape-15368158212.html.</p> 

<p>The following article from Frontiers in Plant Science Agroecology will be useful to understanding the general challenges and opportunities of terrace agriculture: https://www.frontiersin.org/articles/10.3389/fpls.2017.00331/full</p>

<p>To educate terrace farmers on the process of dew collection and inexpensive enhancements on the procedure that has been previously discussed, refer to this short video accessible through Youtube.com : https://youtu.be/ajbodAFqNbA</p>
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       <h3 class="title-bg">References </h3>
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<p>1.	Agnoletti, M. (2012) Italian Historical Rural Landscapes (page 522), Springer.</p>
<p>2.	Jin, Y., Zhang, L., & Wang, P. (2017). Atmospheric Water Harvesting: Role of Surface </p>
<p>3.	Wettability and Edge Effect. Global Challenges, 1(4), 1700019. doi: 
10.1002/gch2.201700019</p>
<p>4.	 Chapagain T and Raizada MN (2017) Agronomic Challenges and Opportunities for Smallholder </p>
<p>5.	Terrace Agriculture in Developing Countries. Front. Plant Sci. 8:331. 
doi:10.3389/fpls.2017.00331</p>
<p>6. Josh, S.C. and Paini, L.M.S. (2010) Is dew useful for Himalayan plants? Current Science 99, 
1434-1437.</p>
<p>7.	Khahil, B. et al. (2016) A review: dew water collection from radiative passive collectors to 
recent developments of active collectors. Sustainable Water Resources Management 2,71-86</p>
<p>8.	Kidron, G.J. (2000) Analysis of dew precipitation in three habitats within a small arid drainage</p>
<p>9.	 basin, Negev Highlands, Israel. Atmospheric Research 55, 257-270.</p>
<p>10.	Lekouch, I. et al. (2010, May 4). Dew, fog, and rain as supplementary sources of water in south-
	western Morocco. Energy, 36(4), 2257-2265. Retrieved October 3, 2019, from 
     https://www.sciencedirect.com/science/article/pii/S0360544210001362.</p>
<p>11.	Pant, G.B., Pradeep Kumar, P., Revadekar, J.V., Singh, N. (2018) Climate Change in the 
	Himalayas, Springer Publishing.</p>
<p>12.	Muselli, M. (2009) Dew and Rain Water Collection in the Dalmatian Coast, Croatia.</p> 
<p>13.	Atmospheric Research, 92(4), 455-46. Retrieved from 
https://www.sciencedirect.com/science/article/pii/S0169809509000209.</p>
<p>14.	Tarolli, P. (2014) Terraced Landscapes: From an Old Best Practice to Potential Hazard for Soil </p>
<p>15.	Degradation Due to Land Abandonment. Anthropocene, 6, 10-25. Retrieved from 
https://www.sciencedirect.com/science/article/pii/S2213305414000113</p>
<p>16.	Takenaka, N. (2003). Difference in Amounts and Composition of Dew from Different Types of 
	Dew Collectors. Graduate School of Engineering, Osaka Prefecture University, 147(1-4), </p>
<p>17.	51-60. Retrieved from https://link.springer.com/content/pdf/10.1023/A:1024573405792.pdf</p>
<p>18.	Werby, Christopher. (2011) DRIPS Dew Collection Project Video. Retrieved from 
https://youtu.be/ajbodAFqNbA</p> 
<p>19.	XiChena, & YinYipab, N. (2019, June 20). Low-temperature heat utilization with vapor </p>
<p>20.	pressure-driven osmosis: Impact of membrane properties on mass and heat transfer Journal of Membrane Science, 588 (1-2) Retrieved October 3, 2019, from 
	https://www.sciencedirect.com/science/article/pii/S0376738819307240</p>