Periodic variations of karstic spring discharge and precipitation from the perspective of wavelet analysis techniques: a case study of tacin spring (Kayseri, Türkiye)

Abstract

Global climate change is just one of the pressures which water resources and their management will face in the upcoming years. To evaluate the impacts of climatic pressure on Tacin karstic spring in water management, this research aims to understand between the role of precipitation on the spring discharge using wavelet analysis techniques. Here, advanced wavelet analysis techniques such as Continuous Wavelet Transform (CWT), Cross Wavelet Transform (XWT), Wavelet Power Spectrum (WPS) and Wavelet Transform Coherence (WTC) were used. This research is the first application of these wavelet techniques in the region and provides new insights into the hydrological dynamics of the karstic system. In addition to Principal Component Analysis (PCA) and Thiessen Polygon Method (TPM), which have been used in many studies in the literature to identify the dominant patterns of variability in multiple rainfall time series, we also used dimensionality reduction techniques such as the Median-Based Reduction (MBR) method, which we introduced to the literature for the first time in this study. In this study, we leveraged 57 years of concurrent monthly data covering precipitation and spring discharge across Kayseri, Pınarbaşı, Gemerek, and Şarkkışla (1965–2022). The results show that the karstic spring discharge (2–6-year scale, 7–10-year scale, 10–15-year scale, 15–24-year scale and 25–30-year scale) and precipitation (3–6-year scale, 5–12-year scale, 13–21-year scale and 21–30-year scale) all have multi-year periodic variations, which might be controlled by climate. During the short-term interval, precipitation exhibited variations occurring over a span of 9–15 months, while the discharge rate demonstrated changes on a scale of 8–16 months. The hydraulic response time of the spring to precipitation is nearly at 78–82 days. Based on the findings of the analysis, it can be inferred that the distinct periods and time series of precipitation and discharge correlate with the heterogeneous structure of the karstic spring and the reservoir volume.