INSIGNIFICANT GRACE TOTAL WATER STORAGE SEASONAL CYCLE IN NORTH AFRICA BETWEEN 1980 AND 2014 BASED ON AN ASSOCIATION OF HYDROLOGICAL VARIABLES AND CLIMATE TELECONNECTIONS

The magnitude and spatiotemporal variations of the groundwater (GW) recharge are the least well-known components in the water cycle in the arid and hyper-arid climate zones (e.g., Northern Africa) due to the sporadic occurrences and difficulty of observations. Yet, recent studies based on GRACE (Gravity Recovery and Climate Experiment) satellites and land surface modeling on the Nubian sandstone aquifer system (NSAS) and North-Western Sahara Aquifer (NWSA) concluded a seasonal recharge of the deep aquifers due to precipitation events over the aquifers and surroundings. Such a conclusion is critical in terms of the sustainable management of fossil GW resources and food (in)security in North Africa due to fossil GW- irrigation. In this study, we assess the periodic components (mode of variability) and frequency of the total water storage (TWS) and precipitation (P) over these aquifers and surroundings using wavelet methodology based on GRACE data and global hydrological modeling between 1980 and 2014. Both P and TWS are compared with seven climate teleconnections indices in searching for a causal relationship. The statistically significant periods are reconstructed at a threshold of (p-value=0.05). Preliminary results show that both aquifers have a dominant interannual cycle (>2.5 years (yr)). While the interdecadal period (21 yr) is more pronounced in TWS in NSAS, the seasonal cycle has more power in the TWS of the NWSA. The coherence between the TWS and climate variability indices is mostly between (2-5 yr) in both aquifers. Further analysis is needed to address the phase differences between the climate indices and hydrologic variables and partitioning the precipitations in the Sahara aquifers. Reconstructing the historical TWS based on hydrologic modeling sheds a new insight in understanding the Sahara hydrological cycle.