تغير المناخ واستخدام المياه للري
في منطقة القصيم المملكة العربية السعودية
رسالة دكتوراه
مقدمة في جامعة إيست أنقليا بمدينة نورج بريطانيا
عبد الله عبدالرحمن المسند
1426هـ
قسم الجغرافية كلية العلوم العربية والاجتماعية
CLIMATE CHANGE AND WATER USE
FOR IRRIGATION: A CASE STUDY IN
THE GASSIM AREA OF SAUDI ARABIA
Abdullah Almisnid
July 2005
A thesis submitted to the School of Development Studies at the University of East Anglia in fulfilment of the requirements
for the degree of Ph.D.
CLIMATE CHANGE AND WATER USE FOR IRRIGATION: A CASE STUDY IN THE GASSIM AREA OF SAUDI ARABIA
Abdullah Almisnid
2005
Abstract
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 ( ETo ) 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 1°C 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 Gassim.
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.
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