**2.4. Water-use evaluation in Africa**

of each 30 minutes, and the change in soil heat storage (dS) above the heat flux plates can be

dS = VC × ((T final − T initial)/1800) × D (2)

where VC = apparent volumetric heat capacity of the soil; T final and T initial = final and initial temperatures for a 30 minute period, and D = 0.04 m = depth of the heat flux plate. The value 1800 is the number of seconds for each 30 minutes. The VC is calculated as the product of the apparent soil density and the specific heat. The soil heat flux density at 0.04 m depth (G0) is calculated as the mean of the two heat flux plate measurements. Then the soil heat flux

G = dS + Go (3)

Temperature data was collected at a frequency of 4 Hz and the time lags of r = 0.25 and 0.5 s were used in a structure function to determine the temperature ramp amplitude (Ar) and inverse ramp frequency (D + S) as described [8]. The uncalibrated sensible heat flux density (H′).

H′ = q × Cp × ((Ar)/D + S)) × Z (4)

and Z is measurement height (m). A calibration factor (f) was used to account for uneven heating below the temperature measurement height and other potential issues [9] and to convert

H = f × H′ (5)

The 'f' values depend on the thermocouple size, sampling frequency, height above the ground, and the underlying vegetation [8–10]. A calibration factor was be determined using a linear regression of sonic anemometer H readings versus H′ data collected over a one-week period

Reference evapotranspiration (ETo) was based on FAO-penman Montheith [11, 12]. Determination of crop coefficient (kc) and actual and maximum evapotranspiration (ETa and ETc):

kc = ETc/ETo (6)

); Cp = specific heat at constant pressure (J kg−<sup>1</sup> K−<sup>1</sup>

) of the air;

computed as in Eq. (2):

80 Soil Moisture

density at the surface (G) was calculated as:

where q is air density (kg m−<sup>3</sup>

on the site.

**2.3. Calculating surface renewal sensible heat flux**

the uncalibrated H′ to the actual sensible heat flux density.

from Eq. (1), LE can be related to ETc or ETa;

Water applied at each site was evaluated based on water held in the soil and data from production and harvest. Water-use efficiency is used as an important parameter to evaluate the performance of this technology. The water-use efficiency is calculated using harvest yield (kg) per m<sup>3</sup> of water applied to the crop. Water consumed (m3 ) is obtained from the analysis of the hydrologic balance, and real evapotranspiration is calculated from measurements using the technique of surface renewal. Rainfall data were measured using a rain gauge installed at the site. Irrigation water was measured and applied using a gauged watering bucket. In the article "Evaluating water productivity of tomato, pepper and Swiss chard under clay pot and furrow irrigation technologies in semi-arid areas of northern Ethiopia" more detail about the agronomic data was presented [13]. A comparative study has been undertaken between bar shaped clay pot and furrow irrigation on tomato, pepper and Swiss chard plots in Mekelle University Campus, Tigray, Ethiopia. Plant height for both tomato and pepper was measured every week using a ruler starting from 30 days of transplanting until maturity. The number of fruits per plant and yield were measured during the cropping season, and the results showed that there were five successive harvests of tomato and Swiss chard whereas there were only two harvests from the pepper crop.
