Shade cloth above the waves will facilitate evaporation

Without nets:
Often the wind blows almost saturated air along the surface of the sea. Because the air is almost saturated not much evaporation occurs into the air. The spray is blown along with the wind - the wind does not blow over the spray and the velocity of the wind relative to the spray is small because they are travelling at about the same speed. So there is not much evaporation of the spray. Also, the spray falls to the sea surface fairly quickly if the droplets are large and then little evaporation occurs.
With nets:
The spray will be caught in the coarse sail cloth nets. The wind will blow through the stationary nets and the wind will therefore have a high speed relative to the wet nets (the water is not blowing along with the wind) and this will facilitate evaporation.
The nets will hold water above the sea surface for a long time, enhancing evaporation.
The nets will provide a large wet surface, with air that is drier than the air being blown along the sea surface, blowing through them, enhancing evaporation,
The nets will be heated in the sun, enhancing evaporation.
Air pressure will build up at the nets and spray will be lifted over the top of the nets, increasing spray area.
Wind speed at the height of the nets will be greater than the wind speed at the surface of the sea, enhancing evaporation.
NOTE: With sea and land breezes the same air tends to move back and forth from land to sea and sea to land. So air could be blown back and forth through the wet nets and humidification could increase every day with each blowing of air through the wet nets. See https://pdfs.semanticscholar.org/4756/b65ef5715dc4bf4ce1b9ab4287c0fbe89cbb.pdf

Cooling air using vegetation

Spekboom could cool the ground in dry areas and enhance rainfall. Sand has air between the grains and this causes sand to act as an insulator concentrating the solar energy in the top few cm of dry sandy soil. So sand gets very hot and heats the air above it by contact and infrared radiation. While sand could reach a temperatures of 60 deg C or so I think Spekboom would be a lot cooler. Leaves of trees and Spekboom, etc, act like "convection machines" because there is a large leaf area at the top of trees, etc, (where leaves are heated in the sun) in contact with the air. So the tree is air-cooled.
If you cool the ground you cool the air above it and the lifted condensation level (LCL) is reduced making rain more likely when the air is lifted by blowing up mountains, etc. The equation is LCL=125(Tair-Tdew) where LCL is in m, Tair is the air temperature in deg C and Tdew is the dew point temperature in deg C.
If you just heat or cool air the dew point temperature remains the same, so cooling air reduces the LCL (height to which air must be lifted for clouds to form). The dew point temperature depends only on the water vapour pressure in the air. Since the atmospheric pressure remains the same and the mole fraction of water vapour remains the same when air is heated or cooled and vapour pressure in the air is (mole fraction of water vapour)x(atmospheric pressure), the dew point remains the same.
Cooling air reduces vapour pressure deficit.

Lambert's Bay Tues 3 Sept 2019, 13:00

Lambert's Bay Tues 3 Sept 2019, 13:00
From weather report: T=23 deg C and RH=41%. 
For all the following calculations the atmospheric pressure is assumed to be 101.325 kPa and the efficiency of evaporative cooling is 30% ( see https://en.wikipedia.org/wiki/Evaporative_cooler#Performance ):
With evaporative cooling of 30% efficiency the air will be cooled to 20.59 deg C. 
RH after evaporative cooling will be 54.08%. 
Volumetric heat capacity of air before cooling is 1.2026 kJ/(m^3.degC)
Using Espy's equation for lifted condensation (LCL):
LCL before evaporative cooling is 1744 m
LCL after evaporative cooling is 1200 m.
The mass of water required to do the evaporative cooling is 1181 tonnes per cubic km.
Dew Point:
Dew point before evaporative cooling is 9.05 deg C
Dew point after evaporative cooling is 10.98 deg C
Danger of fire. The greater the Chandler Burning Index the greater the danger of fire:
Before evaporative cooling: Chandler burning index is 32.86 (fire is unlikely)
After evaporative cooling: Chandler burning index is 14.62 (fire is unlikely)
Saturated adiabatic lapse rate (SALR):
Before evaporative cooling initial SALR is 5.36 deg C per km rise.
After evaporative cooling initial SALR is 5.17 deg C per km rise.
Absolute humidity:
Before evaporative cooling the absolute humidity is 8.43 grams of water vapour per cubic metre.
After evaporative cooling the absolute humidity is 9.67 grams of water vapour per cubic metre.
Discomfort Index (DI). Above 110 is hazardous to health.:
Before evaporative cooling the DI is 79.4
After evaporative cooling the DI is 76.3
Water from air from condensation by cooling air:
Before evaporative cooling you can get 0.38 kg of water per kWh of cooling
After evaporative cooling you can get 0.49 kg of water per kWh of cooling
Vapour pressure deficit (VPD). Usually VPD should be between 0.45 kPa and 1.25 kPa:
Before evaporative cooling VPD is 1.66 kPa
After evaporative cooling VPD is 1.11 kPa

Walvis Bay Sunday 1 Sept 2019, 14:00

Also see https://www.facebook.com/Vapour-Pressure-Deficit-104605390919823/
Walvis Bay, Wednesday 1 Sept 2019 at 14:00.
T=19 deg C and RH=41%. 
For all the following calculations the atmospheric pressure is assumed to be 101.325 kPa and the efficiency of evaporative cooling is 30%:
With evaporative cooling of 30% efficiency the air will be cooled to 16.85 deg C. 
RH after evaporative cooling will be 54.34%. 
Volumetric heat capacity of air before cooling is 1.2186 kJ/(m^3.degC)
Using Espy's equation for lifted condensation (LCL):
LCL before evaporative cooling is 1692 m
LCL after evaporative cooling is 1158 m.
The mass of water required to do the evaporative cooling is 1066 tonnes per cubic km.
Dew Point:
Dew point before evaporative cooling is 5.46 deg C
Dew point after evaporative cooling is 7.59 deg C
Danger of fire. The greater the Chandler Burning Index the greater the danger of fire:
Before evaporative cooling: Chandler burning index is 31.68 (fire is unlikely)
After evaporative cooling: Chandler burning index is 13.66 (fire is unlikely)
Saturated adiabatic lapse rate (SALR):
Before evaporative cooling initial SALR is 5.78 deg C per km rise.
After evaporative cooling initial SALR is 5.56 deg C per km rise.
Absolute humidity:
Before evaporative cooling the absolute humidity is 6.68 grams of water vapour per cubic metre.
After evaporative cooling the absolute humidity is 7.79 grams of water vapour per cubic metre.
Discomfort Index (DI). Above 110 is hazardous to health.:
Before evaporative cooling the DI is 69.8
After evaporative cooling the DI is 66.9
Water from air from condensation by cooling air:
Before evaporative cooling you can get 0.271 kg of water per kWh of cooling
After evaporative cooling you can get 0.405 kg of water per kWh of cooling
Vapour pressure deficit (VPD). Usually VPD should be between 0.45 kPa and 1.25 kPa:
Before evaporative cooling VPD is 1.296 kPa
After evaporative cooling VPD is 0.876 kPa

Walvis Bay 28 Aug 2019, 15:00

Walvis Bay, Wednesday 28 August 2019 at 15:00.
T=18 deg C and RH=58%. Atmospheric pressure is assumed to be 101.325 kPa. 
With evaporative cooling of 30% efficiency the air will be cooled to 16.57 deg C. 
RH after evaporative cooling will be 68.48%. 
Using Espy's equation for lifted condensation (LCL):
LCL before evaporative cooling is 1047 m
LCL after evaporative cooling is 727 m.
The mass of water required to do the evaporative cooling is 711 tonnes per cubic km.
Dew Point:
Dew point before evaporative cooling is 9.62 deg C
Dew point after evaporative cooling is 10.75 deg C
Danger of fire. The greater the Chandler Burning Index the greater the danger of fire:
Before evaporative cooling: Chandler burning index is 10.75 (fire is unlikely)
After evaporative cooling: Chandler burning index is 4.29 (fire is unlikely
Saturated adiabatic lapse rate (SALR):
Before evaporative cooling initial SALR is 5.327 deg C per km rise.
After evaporative cooling initial SALR is 5.215 deg C per km rise.
Absolute humidity:
Before evaporative cooling the absolute humidity is 8.909 grams of water vapour per cubic metre.
After evaporative cooling the absolute humidity is 9.657 grams of water vapour per cubic metre.
Discomfort Index (DI). Above 110 is hazardous to health.:
Before evaporative cooling the DI is 70.4
After evaporative cooling the DI is 68.5
Water from air from condensation by cooling air:
Before evaporative cooling you can get 0.479 kg of water per kWh of cooling
After evaporative cooling you can get 0.556 kg of water per kWh of cooling
Vapour pressure deficit (VPD). Usually VPD should be between 0.45 kPa and 1.25 kPa:
Before evaporative cooling VPD is 0.867 kPa
After evaporative cooling VPD is 0.594 kPa