Water resources need to be managed on a watershed basis and in harmony with other natural resources, while they also need to be consistent with the principle of sustainable development. The basic mean of achieving these conditions is a continuously updated and adaptable watershed information system. In our country, the concept and philosophy of “watershed information system” is not yet established. Therefore, even in the initial stage of watershed management, there is a significant shortage [1] . The main target in watershed management is; conservation of natural resources, bringing the environment into a state where it can renew itself, and sustainable management of resources. Geographical Information Systems (GIS) are seen as a technological and indispensable tool for the preparation of the environments necessary for the collection of the data for the basin and its storage in the digital environment [2] .

In basin management planning, spatial distributions of climate data can be produced in different layers by using point observation values with the aid of GIS. This situation has made the use of GIS inevitable. If the spatial distribution of climate parameters is to be determined and the corresponding climate layers are produced, it is possible to encounter multiple methods. However, the method suitable for one region is not suitable for another region. For this reason, it is necessary to apply similar studies to each region with different methods depending on the characteristics of the region and the structure of the data [3] . That being the case, the determination of the method which is best suitable for each region or basin becomes a problem.

Evaporation, temperature, precipitation climate data are spotted at meteorological observation stations. Since the data are obtained in this way, they are point-shaped in the basin. Therefore, spatial distributions using point data and climate data need to be generated in different layers in the GIS environment. Thus, relationships between data layers can be investigated and interrogation possibilities can be achieved. In studies on the development of water resources, the average areal precipitation depth over a given area is used instead of point precipitation values [4] .

In the survey, 250 raster maps (scanned and positioned) and vector (digital map) maps, 106 geological digital maps (with European Datum 1950 (ED50)-UTM 35N - 36N, with 1/25,000 scale covering the Porsuk basin and neighboring basins around the basin Zone coordination system) have been obtained from the III. Regional Directorate of General Directorate of State Hydraulic Works (DSI). From these maps, Digital Elevation Model (DEM) was created. Digital Elevation Models (DEMs) are a type of raster GIS layer. Raster GIS represents the world as a regular arrangement of locations. In a DEM, each cell has a value corresponding to its elevation. The slope, elevation, elevation and relief maps of the basin are derived using the digital elevation model. With hydrological models, hydrological boundaries of the basin and synthetic drainage network have been obtained. The data required to determine the long-run magnitudes of the meteorological characteristics of the basin (evaporation, temperature, precipitation) were obtained from the General Directorate of State Meteorology Affairs (DMI). The Meteorological Observation Station (MOS) data are taken as monthly averages covering the years 1991-2011. In the Microsoft Excel environment, the data were analyzed and arranged according to the MOS data of each province. Coordinates of each province are transferred to GIS environment. To be able to predict correctly with a dataset, the dataset must have a normal distribution. When the obtained meteorological data were examined, it was found that they did not show statistically normal distribution. For a normal distribution of a data set, it is necessary that the Skewness coefficient is zero (0) and the Kurtosis coefficient is close to (3). In addition, mean and median values should be close to each other. Some transformations such as log, ln, sin, cos, tan, and square root have been applied to normalize the data set to make predictions. These values are used in the estimation process based on the transformations that approximate the normal distribution. However, since the temperature distribution is close to the normal distribution in the original values, no transformation is needed. It is aimed to compare these methods using two distance-dependent methods (IDW, Ordinary Kriging).

The research area is Porsuk Creek Basin. Porsuk Basin is a sub-basin of the Sakarya basin and has an area of 11,113.66 km² in northwest Anatolia. The basin lies between 29˚38' - 31˚59' East longitudes and 38˚44' - 39˚99' North latitudes. The basin is 202 km long in the east-west direction and 135 km long in the north-south direction (Figure 1). More than 60% of the basin is mountainous. The surface waters of the Porsuk Basin are collected by the Porsuk Stream and discharge into the Sakarya river at 660 m elevation, after having traveled 436 km in the basin.

Basin-based meteorological data for Porsuk basin requires estimation of the hydrological boundaries of the basin and analysis of the basin surface for estimation and surface analysis. For this purpose, the characteristics of the basin have been determined with the help of digitized maps. Basin’s Digital Elevation Model (DEM) was extracted using 1/25.000 scaled digitized vector maps. The digital elevation model was analyzed by cutting it according to the hydrological basin boundary. The digital elevation model of Porsuk basin and the lower basins are given in Figure 2(a) and Figure 2(b).

The lower basins which make up the main basin have been created from the hydrological analysis based on the digital elevation model. Also by using the digital elevation models, the slope, height and the three dimensional maps have been

derived from CBS environment. Again by using the numerical height model, the drainage area and the boundaries of the lower basins and the flow direction have been determined. Thus, the drainage network and area caused by the precipitation on each sub-basin has been obtained and given in Figure 2(b). Furthermore, main stream for each sub-basin have also been determined in the study.

In this study, important data such as the number of the main streams and secondary streams in each lower basin, total stream lengths, slope of each stream were obtained. The longitudinal sections of main streams have been removed. The total area of the Porsuk Basin is 11,113.66 km² from the hydrological point of view.

Using the digital elevation model of the Porsuk basin, spatial features related to the basin have been derived by obtaining more data and maps of the basin height, slope, view, shaded relief map and so on. Each dataset is an important piece of information in basin planning. The spatial properties of the basin are classified and given in Figures 3(a)-(d).

When the topographic maps of Porsuk basin are examined, it is observed that the basin has elevations ranging between 500 m and 2250 m elevations. 50% of

the Porsuk basin is more than 1200 m in height (Figure 3(a)). The basin generally has a lower gradient than the 15 degree slope. The slope of the area of approximately 72.81 km², which is 0.66% of the Porsuk basin, and it has a topography above 30˚ (Figure 3(b)). Aspect analysis is the geographical angle of the surface to the north. Approximately 3790.96 km² of the survey area is the slopes facing south, southeast and southwest (Figure 3(c)). From the shaded relief map given in Figure 3(d), it is generally possible to see clearly the structure and flat areas of the basin.

The Porsuk basin reflects the regional climatic characteristics of the Central Anatolian Region. However, it is also under the minor influence of the Aegean region. There are climatic differences between the western and eastern parts of the basin. In general, the summers of the Porsuk basin are arid and hot, and the winters are cold and rainy. The meteorological data in the basin is measured by Meteorological Observation Stations (MOS) located in the provinces of Eskişehir, Kütahya, Afyon, Bilecik, Sakarya and Ankara. Data such as measured rainfall (mm), temperature (˚C) and evaporation (mm) of the basin are obtained from the DMI between 1930-2010 (70 years) [5] . These raw data were edited to obtain averages of the monthly average, minimum and maximum values.

The distribution parameters of the data sets were statistically examined before estimating the distance by using the data obtained from the DMI and DSI and by using the distance-based estimation methods. The data set should show normal distribution, so that a reliable estimation can be made. Estimates made with non-normal data sets will not yield reliable results. For this reason, the distribution parameters of precipitation, temperature and evaporation data sets are evaluated statistically. This assessment is shown in Table 1.