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Time series completion using reanalysis data for the investigation of precipitation changes in Greece

Evangelou Panagiotis

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Year 2023
Type of Item Diploma Work
Bibliographic Citation Ευαγγέλου Παναγιώτης, "Συμπλήρωση χρονοσειρών με αξιοποίηση δεδομένων επανανάλυσης για τη διερεύνηση αλλαγών της βροχόπτωσης στον Ελλαδικό χώρο.", Διπλωματική Εργασία, Σχολή Χημικών Μηχανικών και Μηχανικών Περιβάλλοντος, Πολυτεχνείο Κρήτης, Χανιά, Ελλάς, 2023
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The main objective of the thesis is the detection of trends with the aim of investigating the effects of climate change on precipitation for the region of Greece following the ETCCDI (Expert Team on Climate Detection and Indices) protocol. Prior to this, incomplete precipitation time series from the national database "Hydroscope" were verified, infilled, and extended with direct benefit on the consistency of their statistical characteristics and consequently on their usefulness in a number of applications. In the context of the study, the effectiveness of the use of gridded data on the consistency of infilling daily rainfall observations was further investigated. Gridded data from state-of-the-art high spatial resolution datasets (ERA5-Land, CERRA, E-OBS and CHELSA) were used. Hydrological statistical indicators (NSE, KGE) were used to assess the matching skill of each gridded dataset and to evaluate the added value of the data infilling.A pseudo-gaps time series experiment, proved that the use of gridded data consistently, although marginally, improves the accuracy of the filling. The new infill method was applied in twelve (12) representative stations across the different water districts of Greece using data from neighbouring stations and the CERRA reanalysis dataset, which was found to be the most efficient. Data from the filled stations together with data from additional 50 stations across the Greek territory were then used to derive representative statistical indicators on the trend of rainfall characteristics in the recent past, in accordance with the ETCCDI protocol. The aggregate pattern obtained through the study of the trend for each individual indicator is that of a decreasing rainfall trend on average for most areas, however, there are also areas where an increasing trend has been observed, mainly in the northernmost regions of Greece. More specifically, statistically significant trends of the average annual rainfall, at 90% confidence level, were detected for 25% of the stations, which are equally divided between positive and negative.

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