Climate change and water use for irrigation : a case study in the Gassim area of Saudi Arabia
This thesis describes an assessment of the sensitivity of water use in irrigation to
climate change in the Gassim area of Saudi Arabia. The thesis examines
observed climate variability (1971 2000). Estimates of crop water requirements
(CWR) for wheat under current climate conditions are presented along with results
of field studies of irrigation water use on both traditional and commercial farms.
Outputs from three General Circulation Models (GCMs) HadCM3, CGCM2 and
ECHAM4 for current (control) and future (2020s and 2080s) are analysed.
Changes in temperature, relative humidity, wind speed and sunshine duration are
used to calculate future changes in evapotranspiration (P-7 ) and CWR for wheat.
Observed temperature in Gassim (1971-2000) shows a positive trend with a rate
of warming of 0.55°C/decade and an increase in Diurnal Temperature Range
(DTR) (0.30°C/decade). The average annual rainfall is 92 mm, there is a slight
positive trend in rainfall, and the average rate of increase is 3 mm/decade.
Records of groundwater levels in the region highlight a sustained rapid decline
during the last 20 years. Fieldwork results examine the actual water applied (AWA)
and the relative productivity for wheat. ETO, and CWR are estimated based on the
FAO approach for the observed climate, and comparisons are made between
these and AWA.
Climate change scenarios are presented for Saudi Arabia, and Gassim, using the
outputs of the three GCMs with two emissions scenarios (A2, high, and B2, low).
Warming by the 2020s, in comparison to the baseline climate, is between VC and
1.5°C, and by the 2080s, the range is between 3.2°C and 4.9°C. In terms of
rainfall, there is no significant change (annual changes range from -1.7 to 14.9%
and from -9.4 to 17.4% in the 2020s and 2080s, respectively).
ETO, and CWR are projected to increase by about 3% by the 2020s, and by about
12% (A2) and 9% (B2) by the 2080s. A small increase in temperature such as 1 "C
could result in an increase in CWR of about 103 m3/ha/season for wheat in
This is the first integrated study into the possible impacts of climate change on
agricultural water use in the region. Gassim, given no significant increase in
rainfall, will have higher irrigation needs than under even the current climate
conditions, which will put water use for irrigation under greater pressure. Results
from interviews with farm owners and labourers on water use and climate change
highlighted the importance of non-climate factors such as water management