Uydu (Grace) gravimetri yöntemi ile belirlenen su kütlesi değişimlerinin ölçülmüş hidrometeorolojik verilerle karşılaştırılması
Comparison of total water storage changes by grace (Gravity recovery and climate experiment) with satellite gravimetry method and hydrometeorological data
Yazar: MEHMET ANIL KIZILASLAN
Danışman: PROF. DR. BİHRAT ÖNÖZ ; DOÇ. DR. ORAL YAĞCI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Hidrolik ve Su Kaynakları Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Su yeryüzündeki tüm canlılar için hayati önemi olan doğal bir kaynaktır. Su kaynaklarının etkin bir şekilde değerlendirilmesi, suyun öneminin giderek arttığı bu günlerde ülkemizin pek çok bölgesinde çalışma konusudur. Bir ülkede su seviyesinin değişimini gözlemlemek, ülkemiz gibi tarımsal faaliyetlerin yapıldığı yerlerde önem arz etmektedir. Seviye değişimleri pek çok uydu tarafından gözlemlenmekte ve pek çok çalışmada veri olarak kullanılmaktadır. Uydudan elde edilen veriler ile hidrometeorolojik olarak ölçülmüş değerleri kıyaslamak ise verilerin güvenilirliğini artırmaktadır.
Bu çalışmada, 2002 yılının mart ayında fırlatılan GRACE (Gravity Recovery And Climate Experiment) uydusu ölçümlerinden yararlanılarak Türkiye'de seçilen  dokuz adet gridin seviye değişimleri incelenmiştir. Seçilen bölgeleri temsil etmesi adına her bir grid içerisinde kalan meteoroloji istasyonlarından aylık toplam yağış, buharlaşma, kar su eş değeri verileri ile akım gözlem istasyonlarından aylık ortalama akım verileri elde edilmiştir. Değerlendirmeler; Mart 2003 ile Mayıs 2008 arasında aylık olarak yapılmıştır. 
Her bir griddeki seviye değişimlerine, meteorolojik verilere ve ortalama akım verilerine zaman içerisindeki artış veya azalışlarını belirlemek adına Mann- Kendall trend analizi testi ve regresyon analizi yapılmıştır.
Sonuç olarak, 0.05 anlamlılık düzeyinde L1B çözünürlüğünde dokuz gridden üçünün seviye değişimlerinde anlamlı bir azalma, L2 çözünürlüğünde ise 1 gridde anlamlı bir azalma görülmüştür. Aynı anlamlılık düzeyinde yağış ve buharlaşma ölçümlerinde anlamlı bir artış ya da azalış görülmemekle birlikte; yağışlarda bir azalma buharlaşma da ise bir artma görülmektedir. Ortalama akım ölçümlerinde ise 4 akım gözlem istasyonu verilerinde anlamlı bir azalma belirlenmiştir. 
Uydu verileri ile meteoroloji ve akım gözlem istasyonlarından ölçülmüş veriler kullanılarak kutu grafikleri ile çizilmiş ve yer altı suyu değişimleri  incelenmiştir.
Yapılan çalışmanın, su kaynaklarının kullanılmasına ilişkin yapılacak olan çalışmalara yardımcı olması ve bölgenin genel su değişimi ile ilgili referans bilgi vermesi öngörülmektedir.

Abstract:
Water is a vital resource for every living thing on the Earth. The definition by Scientific Hydrological Committee of the US Federal Council for Science and Technology in 1962 is as follows:"Hydrology is a basic and an applied science that treats the waters of the Earth, their occurrence, circulation, and distribution, their chemical and physical properties, and their reaction with their environment, including their relation to living things". Thanks to this definition, hydrology has become a subject matter studies by many other scientific disciplines. Hydrology has a interdisciplinary nature and is in close relation to such sciences as mathematics, physical, and chemistry.
Global warming caused serious problems concerning water resources, which is thought to result in a decrease in agricultural and forestry products, energy shortage, a populations flow from coastal to central areas. 

For the preservation of eco-balance and a sustainable development of human communities, water resources should be exploited in the wisest way possible so as to satisfy the present and future need for water.
Recently, due to the increasing importance of water, efficient use of water resources has been drawing more attention in Turkish academic milieu. It is crucial to monitor the fluctuations in the water levels in agricultural countries like Turkey. These variations are monitored via satellites and used as data in numerous studies. Comparing satellite data with hydrometeorologically obtained data increases the reliability the processed data.
The present study analyses the variations in nine grid levels in Turkey relying on data obtained from GRACE (Gravity Recovery And Climate Experiment), which was launched in March 2002. The satellite is intended to determine the static gravity field of the Earth and its temporal changes. With this satellite, variations in the terrestrial water storage, tidal and atmospheric mass, and glacial mass can be monitored by means of temporal changes in the globe's gravitational force. The measurement of earth's gravitational force and its temporal variations and the determination of their interrelation to climatic changes are among the missions of GRACE. 
GRACE mission consists of two identical satellites orbiting about 220±50 km apart in a circular trajectory 460 km above the Earth at inclination of 89º to the equator. Intersatellite distances which are recalculated every 5 seconds and variations in these distances allow the researchers to monitor temporal mass variations. 
By means of the energy conservation principle, the difference between gravitational forces of the two satellites on the orbit can be measured on the basis of the evaluation of the variations in intersatellite distance, the satellites' positions and velocity and accelerometric data. 
Two types of data are obtained from the satellites; i.e. monthly L2 harmonic gravity field model and L1 satellite on-orbit data. L1B data refers to a sub-set of GRACE data used for the calculation of spherical harmonic coefficient, called L2 data.
The present study primarily focuses on Southeastern Anatolia (in Turkey), where numerous dams were constructed within the framework of GAP (Southeasten Anatolia Project), on which there is little but hard-to-process data, and which neighbours transborder rivers. 
To create a highly representative data set, the study relies on monthly data on total precipitation, evaporation, snow water equivalent from meteorology stations within the grid and monthly average flow estimates from flow observation stations. Measurements and evaluations were performed from March 2003 till May 2008. 
Whether a statistically continuous variation (increase-decrease) occurs in the value of a random variable in a time series (trend) can be revealed via statistical tests. The Mann-Kendall is one of the common trend test, a non-parametric test. 
Mann-Kendall is often times used to analyze and describe such hydrometeorological data as precipitation, temperature, evaporation, and flow. If the data from an observation station continuously increase or decrease over time, then it can be suggested that there is a pattern, i.e. trend. 
Regression analysis is used to estimate whether a statistically significant relationship exists among variables in the system. If so, it is used to obtain the regression equation of this relationship, to produce estimations, and to calculate reliability range of these estimations. 
The level variations in each grid, meteorological data and average current data were analyzed via Mann-Kendall trend analysis and regression analysis to discover probable increases and decreases in these variables over time. 
In conclusion, out of nine grids the analyses of L1B and L2 resolution data revealed a significant (p<0.05) decrease in three grids and in one grid, respectively. No significant increase or decrease was observed in measurements concerning precipitation and evaporation (p<0.05); but an increase in evaporation and a decreasing trend in precipitation were observed. Average flow measurements revealed a statistical significance in four flow monitoring stations.
As indicated in Chapter 3, GRACE is able to remotely sense total vertical variations in water masses; that is, variations in groundwater, soil humidity, surface water, snow and glaciers. It was calculated via the equation;
ΔSHYDROMETEOROLOGIC = monthly total precipitation – monthly total evaporation + monthly total snow water equivalent + monthly average surface flow
The data on groundwater (GW) were not included in the calculation of the ΔSGRACE variable obtained with the hydrometeorological data. So the difference between level variations obtained from ΔSGRACE and ΔSHYDROMETEOROLOGIC would yield significant data on the use of groundwater. 
Box plots established and estimated groundwater changes with satellite data and hydrometeorological data.
Climatic features of the region indicate that the area receives some amount of precipitation in winter. It was also observed that at this time of the year more groundwater is saved in the regions where less irrigation is conducted and less water is used for daily activities. On the contrary, in spring more water is used for irrigation and daily routines due to the reduction in precipitation, which in return causes groundwater depletion. 
Moreover, groundwater is used more in the south grids than the north because less snow melts in the south grids. The least amount of groundwater was observed in summer since at that time of the year the area receives a very little amount of precipitation, groundwater is overused for irrigation, and the need for water to drink and for daily routines is higher than the rest of the year. 
However, in autumn precipitation rates increase again, which means the oscillation between the peak and the bottom values goes back to normal and more groundwater is accumulated, particularly in the north grid.
As a result; for grid 38; ΔSGRACE, precipitation, evapotranspration, surface flow, snow water equivalent increase; for grid 39; ΔSGRACE, evapotranspration, surface flow, snow water equivalent increase, precipitation decrease; for grid 40; precipitation, surface flow, snow water equivalent decrease, ΔSGRACE, evapotranspration increase; for grid 53; precipitation, surface flow, snow water equivalent decrease, ΔSGRACE, evapotranspration increase; for grid 55; precipitation, surface flow (significant), decrease, ΔSGRACE, evapotranspration, snow water equivalent increase; for grid 68; ΔSGRACE (significant), precipitation, surface flow decrease, evapotranspration (significant), snow water equivalent increase; for grid 69; ΔSGRACE (significant), precipitation, surface flow decrease, evapotranspration (significant), snow water equivalent increase and for grid 70; ΔSGRACE (significant), precipitation, surface flow, snow water equivalent decrease, evapotranspration (significant), increase.
For groundwater change; in grid 38, 39, 40, 53, groundwater increase in January, February, March, April, November and December; decrease in May, June, July, August, September and October. In grid 54, 55, 68, 69 and 70 groundwater increase in January, February, March, November and December; decrease in April, May, June, July, August, September and October
Although Turkey is surrounded by water on three sides, wrong irrigation techniques, it is most likely to face water shortage due to the increase in the demand and need for water to drink and for daily use. The current study is intended to investigate the fluctuations in the water storage in the Southeastern Anatolia, which is quite an important region for Turkey. The determination of the variations in the region's groundwater levels has notably helped better understand the variations of an important water resource.
The study is expected to contribute to future research on the exploitation of water resources and to serve as a reference work on variations in the amount of water supplies.