International Science Symposium Status: Proceeding Book ISS2016 (September 1-4, 2016) ID : A1PB

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1 International Science Symposium Status: Proceeding Book ISS2016 (September 1-4, 2016) ID : A1PB Halil Ibrahim Burgan Istanbul Technical University, burgan@itu.edu.tr, Istanbul-Turkey AUTOREGRESSIVE MODELS FOR PREDICTION OF RAINFALL DATA IN AFYON REGION ABSTRACT Synthetic hydrologic can be produced from stochastic model techniques. The autoregressive (AR) model specifies that the output variable depends linearly on its own previous values and on a stochastic term (an imperfectly predictable term); thus the model is in the m of a stochastic difference equation. AR models have been extensively used in hydrology and water resources since the early 1960 s modeling annual and periodic hydrologic time series. Afyon region is selected as study area, because the region has erratic rainfalls and has a flat surface in terms of topography, so the flood risk is higher every time. In this study, the relationship of cross correlation coefficients ( ) and distance between the rainfall stations of Turkish State Meteorological Service (MGM) is investigated. The is monthly total rainfall (mm) and the date is January, 2009 to December, months in Statistical properties of rainfall are calculated as mean, median, standard deviation and autocorrelation coefficient. Autocorrelation coefficients 5-lags are acquired. Contour maps were created 5-lags from x, y and z values of rainfall stations. While creating contour maps, Surfer 8 software which has a good visualization to present graphics is used in this study. The rainfall of selected rainfall stations in the study area as Afyon, Aksehir, Bolvadin, Cay and Emirdag is estimated and the results are presented. Estimations are made using AR(1) and AR(2) models. Keywords: Afyon Region, AR(1) Model, AR(2) Model, Cross Correlation, Rainfall AFYON BÖLGESİ NDE YAĞIŞ VERİSİ TAHMİNİ İÇİN OTOREGRESİF MODELLER ÖZ Sentetik hidrolojik veri stokastik modelleme teknikleri yardımıyla üretilebilmektedir. Otoregresif (AR) model, çıkış değişkeninin doğrusal olarak kendi geçmiş değerlerine ve bir stokastik döneme (eksik tahmin edilebilir dönem) bağlı olduğunu belirtir; böylece model, stokastik fark denklemi mundadır. AR modelleri, 1960 lı yılların başından beri yıllık ve periyodik hidrolojik zaman serileri için hidroloji ve su kaynaklarında yaygın bir şekilde kullanılagelmektedir. Çalışma alanı olarak, bölgenin düzensiz yağışlar ve topografik açıdan düz bir ovaya sahip olması nedeniyle her zaman taşkın riski taşımasından dolayı Afyon Bölgesi seçilmiştir. Bu çalışmada, Meteoroloji İşleri Genel Müdürlüğü (MGM) ye ait yağış gözlem istasyonları arasındaki uzaklık ile çapraz korelasyon katsayıları ( ) arasındaki ilişkileri araştırılmıştır. Veri, aylık toplam yağış (mm) olup 2009 yılı Ocak-Aralık arasındaki dönemi kapsamaktadır. Yağış verisinin istatistiksel özellikleri, ortalama, medyan, standart sapma ve otokorelasyon katsayısı şeklinde hesaplanmıştır. Otokorelasyon katsayıları, 5 gecikme zamanı adımı için elde edilmiştir. Eşyükselti eğrisi haritaları, yağış gözlem istasyonlarının x, y ve z değerlerinden 5 gecikme zamanı adımı için oluşturulmuştur. Bu çalışmada, eşyükselti eğrisi haritaları oluşturulurken grafiklerin sunumunda iyi bir görselleştirme imkanı sunan Surfer 8 yazılımı kullanılmıştır. Çalışma bölgesinde, Afyon Çay, Bolvadin, Akşehir ve Emirdağ yağış gözlem istasyonları seçilmiştir. Tahminler, AR(1) ve AR(2) modelleri kullanılarak yapılmıştır. Anahtar kelimeler: Afyon Bölgesi, AR(1) Model, AR(2) Model, Çapraz Korelasyon, Yağış 43

2 1. INTRODUCTION Hydrological estimation is complex system. The components of hydrological cycle are basically evaporation, precipitation, groundwater, transpiration and runoff. Estimation of all these steps is too difficult because of system complexity. For example, physical models are based on continuity equations. Operational hydrological ecasting and water resource management require efficient tools to provide accurate estimates of future river level conditions and meet real world demand (Abrahart and See, 2000). The use of autoregressive representation of a stationary time series (or the innovations approach) in the analysis of time series has recently been attracting attentions of many research workers (Akaike, 1969). In this study AR(1) and AR(2) model are used to estimate rainfall in Afyon region. The is monthly total rainfall (mm) and the date is January, 2009 to December, months in Statistical properties of rainfall are calculated as mean, median, standard deviation and autocorrelation coefficient. 2. RESEARCH SIGNIFICANCE Forecasting of streamflow is vital important flood caution, operation of flood-control-purposed reservoir, determination of river water potential, production of hydroelectric energy, allocation of domestic and irrigation water in drought seasons, and navigation planning in rivers (Bayazit, 1988). Also rainfall plays important role to estimate streamflow. Afyon region is important place in terms of thermal waterstourism and agricultural and farming economy. Afyon is located in Central Anatolia and its city neighbors are Eskisehir, Konya, Isparta, Denizli, Usak and Kutahya. Afyon region looks like bowl and it has a big plain which is surrounded high mountains. Theree, in response to flood risk in Afyon in region estimation of rainfall is important. 3. METHOD 3.1. Autoregressive (AR) Model General equation of AR model can be written as below. y i = p å j=1 f j y j-1 + e i f : regression coefficients of model, e : independent variable. AR model can be given as the following matrix (Dogan et al., 2007). é r 1 r 2... r ë p ù = û é ë 1 r 1... r p-1 r r p r 1 r p ù é û ë f 1 f 2... f p-1 ù û (1) (2) 44

3 [ r] = P [ ] [ f] f = P -1 r (3) f values are obtained from eq. (3) and by substituting the following equation, general equation of model can be obtained (Haan, 2002). p y i = åf j y i- j + e i = f 1 y i-1 +f 2 y i-2 + +f p y i- p + e i j=1 (4) 3.2. Data The rainfall observations are Emirdağ, Afyon, Çay, Bolvadin and Akşehir. The is monthly total rainfall (mm) and the date is January, 2009 to December. Station numbers, name and places of stations, coordinates and altitudes of stations are at below table (Table 1). Table 1. Inmations about stations Coordinates(UTM) Station Station Coordinates Altitude X Y No Name-Place (WGS84) (m) Afyon ' N/ ' E Cay ' N/ ' E Bolvadin ' N/ ' E Aksehir ' N/ ' E Emirdag ' N/ ' E RESULTS There are the observations at the stations and mean, standard deviation, median and auto-correlation numbers at the table (Table 2). Table 2. Statistical properties of rainfall at year Station Month Afyon Cay Bolvadin Aksehir Emirdağ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean St. Deviation Auto Correlation C Median There are distances between stations, elevation differences of stations and cross correlations between stations at below table (Table 3). 45

4 Table 3. Cross correlation calculations Stations Distance (km) Elevation Diff. (m) Cross Correlation And in the graphs which are below the x-axis shows distance and elevation difference and y-axis shows cross-correlation coefficients (Figure 1-2). Figure 1. The scatter points of cross correlation coefficient and distance Figure 2. The scatter points of cross correlation coefficient and elevation difference The contour maps versus auto-correlation coefficients (Table 4) were created by Surfer 8 mapping program (Figure 3-7). 46

5 Table 4. Auto-correlation coefficients calculations Auto-correlation Coefficients Station X Y z 1 z 2 z 3 z 4 z Figure 3. The contour map of x, y and z 1. Figure 4. The contour map of x, y and z 2. 47

6 Figure 5. The contour map of x, y and z 3. Figure 6. The contour map of x, y and z 4. 48

7 Figure 7. The contour map of x, y and z AR(1) Model To make AR(1) model the following equation is used, AR(1) yi 1 yi 1 i (5) 11 is generated by AR(1) model and the synthetic is presented with observed (Table 5). All synthetic has =0 and standard deviations are given in Table 6. Obs. Afyon Table 5. Generation of AR(1) model all stations Obs. Synt. Obs. Synt. Obs. Synt. Obs. Cay Cay Bolv. Bolv. Aksehir Aksehir Emird. Synt. Afyon Synt. Emird. Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

8 Table and values AR(1) model Station 1 Afyon Cay Bolvadin Aksehir Emirdag AR(2) Model To make AR(2) model the following equation is used, AR y y y (6) (2) i 1 i1 2 i2 i , 2 2, is generated by AR(2) model and the synthetic is presented with observed (Table 7). All synthetic has =0 and standard deviations are given in Table 8. Obs. Afyon Table 7. Generation of AR(2) model all stations Obs. Synt. Obs. Synt. Obs. Synt. Cay Cay Bolv. Bolv. Aksehir Aksehir Synt. Afyon Obs. Emird. (7) Synt. Emird. Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Table 8. 1, 2, 1, 2 and values AR(1) model Station 1 Afyon Cay Bolvadin Aksehir Emirdag CONCLUSION AND RECOMMENDATIONS Some conclusions are presented below: Black-box models are widely used because of their practicality. But more sensitive studies are required white-box models with more and inmation about study area especially ungauged sites. In this study, only rainfall is estimated. In the following studies, rainfall-runoff models and estimations can be used. 50

9 GIS technology has ongoing developments. So, usage of GIS in hydrological studies will be useful. Afyon region is important in terms of animal and agricultural farming and thermal tourism. So, hydrological estimations are also important in terms of economic and social issues. REFERENCES Abrahart, R.J. and See, L., (2000). Comparing neural network and autoregressive moving average techniques the provision of continuous river flow ecasts in two contrasting catchments. Hydrological Processes, 14, Akaike, H., (1969). Fitting autoregressive models prediction. Annals of the Institute of Statistical Mathematics, 21(1), Bayazit, M., (1988). Hidrolojik modeller. ITU Matbaasi, Istanbul (in Turkish). Dogan, E., Isik, S., Toluk, T., and Sandalci, M., (2007). Daily streamflow ecasting using artificial neural networks. International Congress on River Basin Management, Antalya. Haan, T., (2002). Statistical Methods in Hydrology, Lowa State Pres. 51