Trend and Frequency Analyses of Rainfall in North West Geopolitical Zone of Nigeria

Year 2014, Volume: 4 Issue: 2, 65 - 77, 30.06.2014

Abubakar Ismail Isaiah Adesola Oke

Abstract

The major occupation of people in the North-west geopolitical zone of Nigeria is farming, which
depends on rainfall and other factors. It is well known that climate change has been contributing to change in
amount of rainfall worldwide. In this paper the existence of trend and rainfall frequency analyses were conducted
on rainfall data in North-west geopolitical zone of Nigeria with a particular attention to yearly total rainfalls using
Mann- Kendall and Sen’s slope techniques as well as Pearson log type III distribution. Rainfall data from 1905 –
2008 were collected from ve locations in the region and the test were conducted using standard methods stated in
literature. The study revealed that there are trends in the rainfall in the region and Sen’s test revealed that the trends
are signi cant at 99 % con dence level. Sen’s slopes revealed that there are downward trends in the rainfall for the
last 30 years in all the ve locations. The slopes are -0.94, -6.91; -0.94; -0.84 and -5.66 mm/year for Sokoto, Kano,
Kebbi, Kaduna and Katsina respectively. Rainfall frequency analyses for 2 years return period for these locations
(Sokoto, Kano, Kebbi, Kaduna and Katsina) are 651.08 mm; 844.42 mm 735.68 mm, 1168.47 mm and 669.52 mm
respectively. It was concluded that there are downward trends in the rainfall in last 3 decades for all the locations. 

Keywords

Hydrological data, Rainfall, Sen’s estimator, Trend analysis, Non-parametric tests

Nijerya’nın Kuzeybatı Jeopolitik Bölgesine Düşen Yağış Miktarlarının Eğilim ve Frekans Analizi

Abstract

Nijerya’nın kuzeybatı jeopolitik bölgesinde yaşayan insanların büyük çoğunluğu yağış miktarı ve diğer
faktörlere bağlı olarak tarımla iştigal ederler. İklim değişikliğinin dünya çapında yağıştaki miktar değişimine katkı
sağladığı bilinmektedir. Bu çalışmada mevcut olan yağış frekans ve eğilim analizlerinde Pearson log tip III dağılımı
hem de Mann-Kendall ve Sen’in eğim teknikleri kullanılarak yıllık yağış miktarlarının toplamlarına dikkatle
Nilerya’nın kuzeybatı jeopolitik bölgesindeki yağışlar üzerine odaklanılmıştır. 1905-2008 yılları arasındaki yağış
bilgileri bölgedeki beş yerden toplanmış ve literatürde verilen standart metotlarla test edilmiştir. Çalışma, bölgedeki
yağışlarda eğilimler olduğu, bu eğilimlerin Sen’in testlerine göre % 99 oranında önemli seviyeye sahip olduğunu
ortaya çıkarmıştır. Sen’in eğimleri tüm yerleşim yerlerinde son 30 yılda aşağı doğru eğilimlerin var olduğunu açığa
çıkarmıştır. Eğimler Sokoto, Kano, Kebbi, Kaduna ve Katsina için sırasıyla -0.94, -6.91; -0.94; -0.84 ve -5.66 mm/
yıl şeklindedir. Yağış frekans analizi bu yerleşim yerlerinde 2 yıllık geriye dönük periyotlar için 651.08 mm; 844.42
mm 735.68 mm, 1168.47 mm ve 669.52 mm (Sokoto, Kano, Kebbi, Kaduna ve Katsina) sırasıyla ölçülmüştür. Tüm
yerleşim birimlerinde son 30 yılda yağışta azalma eğilimi olduğu tespit edilmiştir. 

Keywords

Hydrolik veriler, yağış, trend analizi, parametrik olmayan testler

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