Quality control and homogeneity of annual precipitation data in Büyük Menderes Basin, Turkey

Abstract

Precipitation is one of the most impotant climatic factors affecting agricultural production. Knowledge about spatial variability of precipitation amount over an agricultural area, its temporal change not only throughout a year but also over long-term span, start, end and length of rainy period, risk of wet and dry periods would be needed for appropriate agricultural planning and water management issues. However, analysis of long-term precipitation data for various purposes to be accurate, precipitation data must be homogeneous. It is defined that, as for other climatic time series, a homogeneous precipitation time series is to be affected by only natural weather and climatic conditions. Non-climatological factors such as changes in instrument, relocation of station, changes in observation practices make any climatic time series inhomogeneous. In this study, a quality control process involving outlier trimming and homogeneity checking were applied to 20 annual precipitation time series of various lenghts in Buyuk Menderes Basin, Turkey. Homogeneity analysis were performed using the Pettitt test and the Buishand range test. The results of the tests showed that 8 out of 20 stations can be considered to be inhomogeneous whose change points were found to be significant at 5% level by either one or both tests.