Links between GRACE water storage and NAO-EA-SCAND climate patterns in Iberia

Neves, Maria C.; Neves, Rui G. M.

http://hdl.handle.net/10400.1/26846

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Authors

Neves, Maria C.

Neves, Rui G. M.

Abstract(s)

Groundwater drought develops as a smoothed and delayed response to persistent or frequent deficits in rainfall, or as result of a continued negative balance between recharge and extraction. Although not as accurate as in-situ observations, remote sensing has the advantage of providing near real-time and spatially continuous data. GRACE satellite data has been used to show evidence of groundwater depletion in aquifers all over the world (Rodel et al. 2018), and NASA currently generates weakly groundwater and soil moisture drought indicators based on GRACE-FO as part of the United States drought monitoring program. In Europe the Copernicus Global Drought Observatory also uses GRACE total water storage (TWS) anomalies as a proxy of groundwater drought. The use of GRACE satellite data for water resources management, particularly for groundwater systems in the Iberia Peninsula, looks promising (Neves et al. 2020), but its suitability to monitor drought requires further research. On the other hand, large scale atmospheric circulation patterns also known as teleconnections control the interannual to interdecadal natural variability of the climate system. In the Iberian Peninsula, the North Atlantic oscillation (NAO), the East Atlantic (EA) and the Scandinavian (SCAND) patterns are the three main modes of variability driving winter precipitation, river flow and therefore surface and subsurface water storage. These patterns or modes of variability are characterized by indices which measure the strength of atmospheric pressure anomalies. Positive and negative phases of the indices, defined by values above or below given thresholds(e.g. NAO+ is defined for aggregates of winter month indices above 0.5), are generally associated with either wet or dry conditions. Previous studies have shown that wintertime NAO+ and EAphases potentiate droughts in Iberia, the opposite occurring for NAO- and EA+ phases. However, few studies have recognized the importance of interactions amongst climate patterns and only recently did we become aware that their combinations or superpositions, as well as the temporal shifts in their synchronization, may lead to major anomalies in groundwater storage (Neves et al. 2019). The purpose of the present study is to address the question: Do combined NAO-EA-SCAND phases also produce noticeable extremes in GRACE TWS observations? This question is relevant for two main reasons. First, GRACE offers a unique opportunity of fast and reliable large-scale monitorization of groundwater and can be used as an early warning system for groundwater drought or aquifer depletion. Second, the NAO-EASCAND indices provide a potential source of seasonal forecast since their wintertime value determines the availability of water in the following summer. Teleconnections may also be a source of long-term forecasting as they exert periodic controls on groundwater level and are linked to recurrent droughts.