Climate variability is important to understand as its effects on groundwater are complex than surface water. Climate association between Groundwater Storage (GWS) and sea level changes have been missing from the Intergovernmental Panel on Climate Change, demanding a requisite study of their linkage and responses. The current dissertation is primarily focused on the ongoing issues that have not been focused on the previous literatures. Firstly, the study evaluated the effects of short-term persistence and abrupt shifts in sea level records along the US coast by utilizing popular robust statistical techniques. Secondly, the study evaluated the variability in groundwater due to variability in hydroclimatic variables like sea surface temperature (SST), precipitation, sea level, and terrestrial water storage. Moreover, a lagged correlation was also analyzed to obtain their teleconnection patterns. Lastly, the relationship between the groundwater rise and one of the most common short-term climate variability, ENSO was obtained. To accomplish the research goals the current dissertation was subdivided into three research tasks.The first task attempted to answer a major question, Is sea level change affected by the presence of autocorrelation and abrupt shift? This question reflects the importance of trend and shift detection analysis in sea level. The primary factor driving the global sea level rise is often related to climate change. The current study investigates the changes in sea level along the US coast. The sea level records of 59 tide gauge data were used to evaluate the trend, shift, and persistence using non-parametric statistical tests. Mann-Kendall and Pettitt’s tests were utilized to estimate gradual trends and abrupt shifts, respectively. The study also assessed the presence of autocorrelation in sea level records and its effect on both trend and shift was examined along the US coast. The presence of short-term persistence was found in 57 stations and the trend significance of most stations was not changed at a 95% confidence level. Total of 25 stations showed increasing shift between 1990–2000 that was evaluated from annual sea level records. Results from the current study may contribute to understanding sea level variability across the contiguous US. The second task dealt with variability in the Hydrologic Unit Code—03 region. It is one of the major U.S. watersheds in the southeast in which most of the variability is caused by Sea Surface Temperature (SST) variability in the Pacific and Atlantic Ocean, was identified. Furthermore, the SST regions were identified to assess its relationship with GWS, sea level, precipitation, and terrestrial water storage. Temporal and spatial variability were obtained utilizing the singular value decomposition statistical method. A gridded GWS anomaly from the Gravity Recovery and Climate Experiment (GRACE) was used to understand the relationship with sea level and SST. The negative pockets of SST were negatively linked with GWS. The identification of teleconnections with groundwater may substantiate temporal patterns of groundwater variability. The results confirmed that the SST regions exhibited El Niño Southern Oscillation patterns, resulting in GWS changes. Moreover, a positive correlation between GWS and sea level was observed on the east coast in contrast to the southwestern United States. The findings highlight the importance of climate-driven changes in groundwater attributing changes in sea level. Therefore, SST could be a good predictor, possibly utilized for prior assessment of variabilities plus groundwater forecasting. The primary goal of the third task is to better understand the effects of ENSO climate patterns on GWS in the South Atlantic-Gulf region. Groundwater issues are complex and different studies focused on groundwater depletion while few emphasized, “groundwater rise”. The current research is designed to develop an outline for assessing how climate patterns can affect groundwater fluctuation, which might lead to groundwater rise. The study assessed the effect of ENSO phases on spatiotemporal variability of groundwater using Spearman Rank Correlation. A significant positive correlation between ENSO and GWS was observed. An increasing trend was detected in GWS where most grids were observed in Florida by utilizing the non-parametric Mann-Kendall. A positive magnitude of the trend was also detected by utilizing Theil-Sen’s Slope method with high magnitude in the mid-Florida region. The highest GWS anomalies were observed in the peak of El Niño events and the lowermost GWS was observed during La Niña events. Furthermore, most of the stations were above normal groundwater conditions. This study provides a better understanding of the research gap between groundwater rise and ENSO.

Le niveau de la mer est une des variables climatiques essentielles dont la variabilité résulte de nombreuses interactions complexes entre toutes les composantes du système climatique sur une large gamme d'échelles spatiales et temporelles. Au cours du XXème siècle, les mesures marégraphiques ont permis d'estimer la hausse du niveau de la mer global entre 1,6 mm/an et 1,8 mm/an. Depuis 1993, les observations faites par les satellites altimétriques indiquent une hausse du niveau de la mer plus rapide de 3,3 mm/an. Grâce à leur couverture quasi-globale, elles révèlent aussi une forte variabilité du niveau de la mer à l'échelle régionale, parfois plusieurs fois supérieure à la moyenne globale du niveau de la mer. Compte tenu de l'impact très négatif de l'augmentation du niveau de la mer pour la société, sa surveillance, la compréhension de ses causes ainsi que sa prévision sont désormais considérées comme des priorités scientifiques et sociétales majeures. Dans cette thèse, nous validons d'abord les variations du niveau de la mer mesurées par la nouvelle mission d'altimétrie satellitaire, SARAL-AltiKa, en comparant les mesures avec celles de Jason- 2 et des marégraphes. Un autre volet de cette première partie de thèse a consisté à estimer les parts respectives des facteurs responsables des variations du niveau de la mer depuis 2003 en utilisant des observations issues de l'altimétrie satellitaire (missions altimétrique Jason-1, Jason-2 et Envisat), de la mission GRACE, et des profils de température et salinité de l'océan par les flotteurs Argo. Une attention particulière est portée à la contribution de l'océan profond non 'vue' par Argo. Nous montrons que les incertitudes dues aux approches du traitement des données et aux erreurs systématiques des différents systèmes d'observation nous empêchent encore d'obtenir des résultats précis sur cette contribution. Dans la deuxième partie de la thèse, en utilisant les données de reconstruction du niveau de la mer dans le passé, nous étudions la variabilité régionale du niveau de la mer et estimons sa hausse totale (composante régionale plus moyenne globale) de 1950 à 2009 dans trois régions vulnérables: l'océan Indien, la mer de Chine méridionale et la mer des Caraïbes. Pour les sites où l'on dispose de mesures du mouvement de la croûte terrestre par GPS, nous évaluons la hausse locale du niveau de la mer relatif (hausse du niveau de la mer totale plus mouvement de la croûte locale) depuis 1950. En comparant les résultats de ces trois régions avec une étude précédente sur le Pacifique tropical, nous constatons que le Pacifique tropical présente la plus forte amplitude des variations du niveau de la mer sur la période d'étude. Dans la dernière partie de la thèse, nous nous concentrons par conséquent sur le Pacifique tropical. Nous analysons les rôles respectifs de la dynamique océanique, des modes de variabilité interne du climat et du forçage anthropique sur les structures de la variabilité régionale du niveau de la mer du Pacifique tropical depuis 1993. Nous montrons qu'une partie importante de la variabilité régionale du niveau de la mer du Pacifique tropical peut être expliquée par le mouvement vertical de la thermocline en réponse à l'action du vent. En tentant de séparer le signal correspondant au mode de variabilité interne du climat de celui de la hausse régionale du niveau de la mer dans le Pacifique tropical, nous montrons également que le signal résiduel restant (c'est-à-dire le signal total moins le signal de variabilité interne) ne correspond probablement pas à l'empreinte externe du forçage anthropique. / Sea level is an integrated climate parameter that involves interactions of all components of the climate system (oceans, ice sheets, glaciers, atmosphere, and land water reservoirs) on a wide range of spatial and temporal scales. Over the 20th century, tide gauge records indicate a rise in global sea level between 1.6mm/yr and 1.8 mm/yr. Since 1993, sea level variations have been measured precisely by satellite altimetry. They indicate a faster sea level rise of 3.3 mm/yr over 1993-2015. Owing to their global coverage, they also reveal a strong regional sea level variability that sometimes is several times greater than the global mean sea level rise. Considering the highly negative impact of sea level rise for society, monitoring sea level change and understanding its causes are henceforth high priorities. In this thesis, we first validate the sea level variations measured by the new satellite altimetry mission, SARAL-AltiKa by comparing the measurements with Jason-2 and tide gauge records. We then attempt to close the global mean sea level budget since 2003 and estimate the deep ocean contribution by making use of observational data from satellite altimetry, Argo profiles and GRACE mission. We show that uncertainties due to data processing approaches and systematic errors of different observing systems still prevent us from obtaining accurate results. In the second part of the thesis, by making use of past sea level reconstruction, we study the patterns of the regional sea level variability and estimate climate related (global mean plus regional component) sea level change over 1950-2009 at three vulnerable regions: Indian Ocean, South China and Caribbean Sea. For the sites where vertical crustal motion monitoring is available, we compute the total relative sea level (i.e. total sea level rise plus the local vertical crustal motion) since 1950. On comparing the results from these three regions with already existing results in tropical Pacific, we find that tropical Pacific displays the highest magnitude of sea level variations. In the last part of the thesis, we therefore focus on the tropical Pacific and analyze the respective roles of ocean dynamic processes, internal climate modes and external anthropogenic forcing on tropical Pacific sea level spatial trend patterns since 1993. Building up on the relationship between thermocline and sea level in the tropical region, we show that most of the observed sea level spatial trend pattern in the tropical Pacific can be explained by the wind driven vertical thermocline movement. By performing detection and attribution study on sea level spatial trend patterns in the tropical Pacific and attempting to eliminate signal corresponding to the main internal climate mode, we further show that the remaining residual sea level trend pattern does not correspond to externally forced anthropogenic sea level signal. In addition, we also suggest that satellite altimetry measurement may not still be accurate enough to detect the anthropogenic signal in the 20 year tropical Pacific sea level trends.