Physical and Chemical Characteristics of Dew and Rain in North-West Africa with Focus on Morocco: Mapping Past and Future Evolution (2005–2100)

Abstract

In the context of global warming and a reduction in fresh water availability, this study presents the evolution of dew, rain and evapotranspiration in the North-West (NW) of Africa. This study is followed by a chemical analysis of dew and rain data in a representative site. The time periods are concerned with the years 2005–2020 using existing data, and years 2020–2100 using the low and high emissions representative concentration pathway scenarios RCP 2.6/8.5 from the coordinated regional climate downscaling experiment database. A continuous decrease in rain precipitation is observed, on the order of −14 mm·decade−1 for the more credible scenario RCP 8.5. The amplitude is maximum on the coast and on the foothills of Atlas. A clear decrease in dew yields (up to 7%) is also observed along a NW/SE axis. It is strongly correlated with a corresponding decrease in relative humidity. Chemical dew and rain data in the representative site of Mirleft correspond to the major cations of Na+ > Ca2+ > Mg2+ > K+, similar to local spring water. The concentrations in rain are about two times less than in dew water. Ionic concentrations are compatible with the World Health Organization standards. The seasonal variations of the ionic concentrations in dew and rain follow a volume dilution dependence. In the future, the expected diminution in dew and rain volumes according to the RCPs 2.6 and 8.5 should increase the dew and rain ionic concentrations.

Evolution of Dew and Rain Water Resources in Gujarat (India) between 2005 and 2021

“…A study by [4] predicts that in the Mediterranean region, dew harvesting may decline (up to 27%) by the end of the twenty first century during the dry season, however, the rate of decrease in dew yield is comparatively lesser than the projected 40% decrease in precipitation during the same period. A trend has been predicted for the North Africa area in another recent study [10]. It reports that for the century a continuous decrease of the order of −14 mm per decade is expected in rain precipitation and a clear decrease of up to 7% in the dew yields may be seen.…”

“…Along with the meteorological factors mentioned above, the dew yield also depends on the material used as condenser as well as the orientation of the condenser to collect dew. The yield can vary by at least 20% at the same location depending on the condenser's orientation with respect to the wind direction and the nearby obstacles [3,8,9,10].…”

Characteristics and Estimation of Dew in the Loess Hilly Region of Northern Shaanxi Province, China

“…The coupling of wind and natural convection enhances the convective heat transfer, and the effect of wind speed on dew can be determined using Equation ( 6) [26]. During the observation process, there is an inevitable local airflow difference around the condensation surface, which affects the heat exchange between the condenser and the air [52]. In terms of the wind speed statistics at 200 cm above the ground, the dew frequency and the dew amount were extremely small when the wind speed was greater than 1.1 m•s −1 .…”

“…The Beysens model primarily uses meteorological factors, that is, wind speed, cloudiness, RH, and air temperature. Natural convection and forced (wind) convection cause heat exchange between the condensation surface and the air variable, such that larger dew events tend to be underestimated, whereas smaller dew events tend to be overestimated [24,52].…”

Re-Engineering Dew-Harvesting Cactus Macrostructures to Enhance Water Collection as an Adaptive Climate Change Strategy: An Experimental Comparison

“…Places such as California are trying to address this problem by looking at fog water using mesh-screed fog collectors [5]; this may not be the only solution, however, due to Californian fog being seasonal, and hence, the potential for harvesting dew is an important consideration. It has been predicted, however, that regions such as Northwestern Africa and the broader Mediterranean basin are projected to endure a significant decline in precipitation and dew yields as a result of climate change due to decreasing relative humidity [6,7]. It will thus become even more critical to enhance the performance of airborne moisture harvesters to adapt to the challenges faced due to climate change.…”