# Long-Term and Decadal Sea-Level Trends of the Baltic Sea Using Along-Track Satellite Altimetry
## 6 Discussion
When compared to the global mean sea level (GMSL) trends obtained from TG and SA data, which exhibited rates ranging from 3.2 mm/yr over the period 1993-2015 to 3.6 mm/yr over the period 2006-2015 [5], the long-term sea-level trend calculated for the Baltic Sea appeared consistent. Importantly, this trend seemed unaffected by the considered time span or the specific data source examined. This study also explored the long-term RSL and ASL derived from TG hourly data spanning 1995-2022. The findings indicate the significance of accounting for VLM in accurately quantifying trend rates (Section 5.1). For instance, in this analysis, the RSL trends ranged from \(-2\) to 4.5 mm/yr, while the ASL trends varied between 2 and 5.4 mm/yr. Notably, given the spatial variability of VLM rates, the most substantial disparities between the RSL and ASL were observed in locations significantly affected by pronounced VLM. Consequently, in the northern and eastern regions of the Baltic Sea, a distinct pattern emerged, where the ASL displayed an increasing trend from south to north, while the RSL exhibited a decreasing trend from north to south, as evidenced, for instance, at the Pori station (#13). This discrepancy highlights the impact of VLM on sea-level measurements in these specific areas. Moreover, the ASL trend derived from satellite altimetry (SA) data can be effectively compared to the RSL trend derived from TG data. This comparison serves the purpose of either refining or validating the models designed to account for VLM. The analysis revealed a spatial variation in sea-level trends within the Baltic Sea region, indicating larger values (ranging from 4 to 5 mm/yr) in the north-eastern section compared to stations situated in the south-west (between 2 and 4 mm/yr). Previous studies, such as by [63], suggested that this discrepancy could be attributed to an escalation in the frequency and intensity of westerly winds. Additionally, an increase in cyclones occurring above 52\({}^{\circ}\)N has exposed the Baltic Sea to more vigorous westerly storms, potentially contributing to these observed trends. Supporting these findings, a recent report by [84] noted a general pattern of rising water temperatures, a reduced ice extent, and an overall uptick in annual mean precipitation across the northern region. Specifically, in the northern Baltic Sea and the Gulf of Finland, there is a statistical association between larger river runoff and warmer air temperatures coupled with increased precipitation. Conversely, in more westerly regions, a decline in annual runoff corresponds with rising air temperatures. These observations collectively support the notion of varied influences impacting sea-level trends across different sections of the Baltic Sea. The long-term trends consistently highlight larger rates in the northern section, aligning with findings from earlier studies. Interestingly, these results reveal an anomaly in certain south-western stations, specifically at Rodvig (#8) and Kungsholmsfort (#10), where higher-than-normal trends of approximately 5.1 mm/yr and 4.8 mm/yr, respectively, were calculated using TG hourly data. These rates notably exceed the trends observed at other south-western stations, which typically range within 2 to 4 mm/yr. These unexpected findings require further investigations for a deeper understanding of the main drivers behind this. Understanding the main drivers behind these discrepancies is crucial for a comprehensive and accurate interpretation of sea-level trends in these specific south-western stations. Examining sea-level trend values at decadal scales revealed notable circumstances. During the period from 2000-2009, a majority of stations (9 out of 13) exhibited an increase in sea-level trends compared to the subsequent decade, 2010-2019. While some stationsmight have been affected by data gaps during this period (Table 4), others remained unaffected.