Ali M. Subyani

Geostatistical study of annual and seasonal mean rainfall patterns in southwest Saudi Arabia / Distribution géostatistique de la pluie moyenne annuelle et saisonnière dans le Sud-Ouest de l’Arabie Saoudite

Abstract Abstract The spatial and temporal variability of rainfall is a major problem in its description and prediction. Saudi Arabia has an extremely dry climate, but in the southwest region comparatively more rainfall events occur within the effects of topography and seasonality. Sixty-three representative stations were selected for a 21-year period covering different micro-climate conditions. Geostatistical methods were used to reflect the regional and seasonal rainfall patterns throughout the southwest region. The results indicate that high variations in regional rainfall estimation occur in the mountainous areas, while the variance decreases in shadow areas in all seasons. The variation of the rainfall estimation accuracy decreases from winter to autumn.

Digital elevation model and multivariate statistical analysis of morphometric parameters of some wadis, western Saudi Arabia

In arid regions, the analysis of wadi morphometric parameters and their interrelationships are fundamental for describing the topographic, geologic evolution, structures and hydrologic potential efficiency of the watershed. Unfortunately, the spatial characteristics and the analyses of these variables are not taken into consideration in an efficient way, especially in arid regions. In this paper, digital elevation model, geographic information system and multivariate statistical techniques are integrated for the identification and the assessment of main morphometric parameters. For this purpose, Q and R modes of cluster analyses and principal component analysis (PCA) are applied to ten different-size watersheds in the western region of Saudi Arabia utilizing 18 morphometric descriptors (variables). The results show that the R-mode cluster analysis classifies the variables into three groups, whereas the Q-mode cluster analysis classifies watersheds according to the similarities in their major variables such as area, perimeter, total stream length and peak discharge. The first three components of PCA accounted for 86% of the total variance in the data and show more details concerning the parameter loadings and the degree of variable significance.الملخصإن تحليل المعاملات المورفومترية وعلاقتها ببعضها البعض في أودية المناطق الجافة تعتبر من الأساسيات لشرح وتفسير الخصائص الطبوغرافية والنشأة الجيولوجية والتركيبية وكذلك الفعالية الهيدرولوجية لأحواض هذه الأودية. وللأسف فإن أودية المناطق الجافة لم تأخذ هذه الخصائص وتوزيعها المكاني بعين الإعتبار. وفي هذا البحث تم استخلاص المعاملات المورفومترية الرئيسية والفرعية لعشرة اودية غرب المملكة العربية السعودية باستخدام نماذج الإرتفاعات الرقمية وتحليل المخرجات باستخدام نظم المعلومات الجغرافية، ومن ثم إستخدام التحليل الإحصائي لمتعدد المتغيرات وذلك لملاحظة العلاقات الداخلية بين عدد 18 من المعاملات أو بين خصائص الأودية نفسها بما يسمي بالتحليل التجميعي Q and R-mode . أظهرت النتائج ان التحليل التجميعي R-mode قد وضع المتغيرات في ثلاثة مجاميع، بينما اظهر التحليل التجميعي بواسطة Q-mode يناءا علي التشابه بين الأحواض المائية من ناحية المساحة والمحيط ومجموع اطوال الأودية وقمة الصريف المائي. أما تحليل المركبات (التحليل العاملي- Factor analysis) في الثلاث مركبات الأول فقد شرحت حوالي 86% من إجمالي التباين في قيم المتغبرات وكذلك اوضحت العلاقة العاملية لكل مركب ودرجات الترجيح للمتغيرات المرتبطة بكل مركب.

Geostatistical modelling of the Wasia aquifer in Central Saudi Arabia

Abstract Aquifers in sedimentary basins provide a regional domain for the spatial variabilities in geologic, hydrologic, geomorphologic and hydrochemical phenomena. Their study should account for this spatial variability within the study area prior to any formal modelling. A cumulative semivariogram scheme is adopted in this paper for the spatial variability, which is then incorporated with the kriging technique to provide maps of regional variation concerning variables such as storativity, transmissivity, piezometric levels, total dissolved solids and groundwater flow velocity. It is shown that the classical semivariogram models are not capable of accounting for the spatial variability of the Wasia aquifer. Comparison between the cumulative and classical semivariograms are given on the basis of hydrogeologic variables observed in the field. It is concluded, in general, that the cumulative semivariogram modelling of the spatial variability is more effective and yields realistic regional variables.

Identifying the hydrochemical processes of groundwater in Wadi Na'man, Western Saudi Arabia using factor analysis

The groundwater of Wadi Na’man, located in the western Saudi Arabia, is subject to intense exploitation to accommodate all the water demands of this arid area. The groundwater of its shallow aquifer undergoes significant decline in water level, increasing salinity due to long time of aridity and irregular rainfall. A multivariate statistical technique, factor analysis, was used to identify and understand hydrochemical association and processes leading to the variability of groundwater quality without losing any information of input pattern and avoid limitations that are associated with classical methods. R- and Q-modes of factor analysis were applied to 63 groundwater samples and 21 variables. This analysis revealed that three factors accounted for 55.9% of the total data variability. Factor 1 was dominated by Ca2+, Mg+, Na+, Cl−, and SO42−, as well as trace elements such as phosphorus and boron, suggesting effects from possible water–soil/rock interaction and agricultural activities. Factor 2 represented high aluminum loading as a result of the weathering of aluminum silicate minerals. Factor 3 revealed negative loading of dissolved CO3 and Zn, indicating long-term aridity. Plots of Factor 1 versus Factor 2 and Factor 3 demonstrated that the samples clustered into one group with good separation from outliers. In addition, assessment of the drinking quality suggested that salinity increases with SO42−–Cl−–Ca2+.الملخصتعتبر المياه الجوفية في وادي نعمان الواقع غرب المملكة العربية السعودية من المصادر الأساسية للمياه في المنطقة حيث تتعرض لإستنزاف شديد يتسبب في إنخفاض منسوب المياه وزيادة الملوحة خاصة ان الوادي يقع في منطقة جافة وقليلة الأمطار. ويعتبر تحليل المتغيرات المتعددة، التحليل العاملي للمركبات، من الوسائل المفيدة في تفسير وفهم العمليات الهيدروكيميائية للمياه الجوفية وتغير كيمائيتها باستبعاد محدودية الطرق التقليدية لتفسير تلك العمليات.أظهرت طريقة تحليل المركبات (التحليل العاملي- Factor analysis) لعدد 63 عينة من المياه الجوفية لوادي نعمان وعدد 21 متغير (عنصر رئيسي ونادر) في الثلاث مركبات الأول التي شرحت حوالي 55.9% من إجمالي التباين في قيم المتغبرات وكذلك اوضحت العلاقة العاملية لكل مركب ودرجات الترجيح للمتغيرات المرتبطة بكل مركب.أظهر العامل الأول سيادة المتغيرات الرئيسية مثل الصوديوم واالمغنسيوم والكالسيوم والكلور والكبريت وكذلك الفوسفور والبورن نتيجة التفاعل بين المياه والتربة وكذلك النشاط الزراعي. أما العامل الثاني فقد تمثل في سيطرة الألمنيوم نتيجة تعرية معادن الألمنيون السليكاتية. وأما العامل الثالث فقد كشف الجانب السلبي للكربونات مما يؤكد طول فترة الجفاف في المنطقة. واظهرت العلاقات بين هذه العوامل وجود مجموعتين مع وضوح العينات الشاذة عنهما.

Flood vulnerability assessment in arid areas, Western Saudi Arabia

In arid regions, flash floods often occur as a consequence of excessive rainfall. Occasionally causing major loss of property and life, floods are large events of relatively short duration. Western Saudi Arabia is an extremely arid region where rainfall is characterized by extremely high spatial and temporal variability. This area is subject to environmental hazards such as flood risks because most of the infrastructure is located on wadis and flood plains. In this paper, an integrated approach was adopted in which geographic information system and rainfall–frequency analysis using annual maximum 24-h rainfall were utilized to identify, assess and mitigate hydrological and environmental flood hazards in the study area. The study shows that the prediction of annual maximum 24-h duration rainfall along with prediction of 25-, 50-, 100- and 200-year return periods for the best fit of Gumbel pdfs. In addition, probable maximum precipitation was also estimated for 50- and 100-year return periods, which will aid decision-making for future project designs and flood protection studies.

Generation of Rainfall Intensity Duration Frequency (IDF) Curves for Ungauged Sites in Arid Region

ObjectiveWe developed a method for Intensity Duration Frequency (IDF) curves in ungauged locations in arid region.BackgroundThe arid climate which covers most of Saudi Arabia is typically characterized by large temporal and spatial variations in rainfall distribution. The availability of long-term records of rainfall-runoff series would be useful to better estimate effective rainfall depth. The development process for an IDF curve for a remote, ungauged site is addressed through the use of rainfall record.MethodThe analyses focused on the application of two distributions: the Gumbel and Log Pearson III functions combined, to estimate the maximum rainfall for the various return periods in three stations in Al-Madinah region.ResultsThe empirical intensity frequency equation is used to estimate rainfall intensity for design purposes for the ungauged location. The results of this research contribute to the development of IDF-based design criteria for water projects in ungauged sites located in arid and extreme arid regions.