Forecasting low flow conditions months in advance through teleconnection patterns, with a special focus on summer 2018

Abstract

Over the past decades, Europe has been affected by several low flow periods which had substantial impacts on the hydrology of the rivers themselves as well as on the society and economy. Low flow periods have a direct impact on the environment, on the inland waterway navigation, on the hydropower production as well as on the sediment management, among others. Similar to floods, low flows are naturally occurring phenomena which can significantly hinder different uses and functions of the rivers and impact the aquatic system and the water quality. Moreover, it is projected that, in the future, climate change might lead to drier summers over the european region and therefore to more frequent and severe low flow periods. The results presented here show that the summer 2018 low flow situation, over the Rhine and Elbe Rivers basin, could have been predicted up to two seasons ahead by using previous months' sea surface temperature, sea level pressure, precipitation, mean air temperature and soil moisture. the lagged relationship between the predictand (e.g. seasonal streamflow) and the climate and oceanic predictors varies between 1 month (e.g. precipitation) up to 6 months (e.g. sea surface temperature). Taking into account that all predictors are available in realtime, the forecast scheme can be used to provide early warnings for the upcoming low flow situations, thus offering the possibility for better management of the water resources. Drought is among the costliest and damaging disasters in the world and is a naturally occurring phenomenon that can affect large land areas and can prevail over extended periods (e.g. several months up to a few years). Over the last two decades, the European region has witnessed a series of long-lasting dry and hot summers (2003, 2010, 2015, and 2018, among others) 1-3. For example, the year 2018 over the central part of Europe, especially Germany, was extraordinarily hot and dry. For Germany, the period April-July 2018 was the warmest since 1,880 and different meteorological stations have reached all-time maximum temperature records. This situation was also exacerbated by a rainfall deficit since February 2018. Overall, in Europe, the monetary losses caused by hydrological and meteorological extremes, over the period 1980-2017, amounted to ~ 453 billion Euro 4. Prolonged dry periods, such as the ones observed in the last decades (e.g. 2003, 2015, and 2018) have emphasized the degree of vulnerability of society to this natural hazard and alerted different governmental agencies and stakeholders regarding the damaging effects drought can have on the economy and society 5,6. Moreover, the IPCC fifth assessment report 7 concludes that the magnitude and frequency of extreme events (e.g. droughts, floods, heatwaves, compound events) will increase globally in the future and large areas of the European continent will be exposed to increased drought risk and possibly to more frequent and long-lasting low flow periods. Prolonged low flow periods may result in several types of issues for the soc...

Non‐stationary control of the NAO on European rainfall and its implications for water resource management

“…Previous work shows many of these areas to have weak to moderate, yet often significant, NAOI‐P correlations; such as for western and northern England (West et al, 2019), northern Germany (Riaz et al, 2017), southern France (Massei et al, 2007). Indeed, many studies in these regions have found skilful prediction of winter rainfall (and other water resource variables) through use of the historical NAOI‐P relationship, despite the non‐stationary reported here (Ionita & Nagavciuc, 2020; Moreira et al, 2016; Rasouli et al, 2020; Rousi et al, 2020; Scaife et al, 2014; Svensson et al, 2015). This apparent contradiction with our non‐stationary correlation results at decadal timescales and results from other studies for multi‐decadal timescales (Pauling et al, 2006; Vicente‐Serrano & López‐Moreno, 2008) can be explained by the common multi‐decadal periods of relative stability in our results, despite general non‐stationarity throughout the rolling correlation series.…”

“…Some forecasting systems seek to project further into the future to allow long‐term planning of infrastructure and resilience to extremes and climate change (Svensson et al, 2015). These systems can rely directly or indirectly on outputs from Global Climate Models (GCMs; such as gridded reanalysis datasets) to forecast hydrological conditions (Bhatt & Mall, 2015; Ionita & Nagavciuc, 2020). In the North Atlantic region, in particular Western Europe, the North Atlantic Oscillation (NAO) is used as an indicator for hydrometeorological conditions given its leading control on winter rainfall totals (Hurrell & Deser, 2010; Scaife et al, 2008, 2014).…”

On the curious case of the recent decade, mid-spring precipitation deficit in central Europe 

“…The rainfall deficit and the high temperatures over the last decade have also led to extremely low river flows. Some of the most important waterways in Europe have been seriously affected, with enormous economic consequences 14 . April 2020, the driest of the last 140 years, has set a new record for low flows in the Elbe River (north-eastern part of Germany) ( Fig.…”

“…Droughts, which can extend over large areas and last for several years, are amongst the most damaging and expensive natural hazards. Since the beginning of the 21st century, Europe has experienced a series of prolonged summer heatwaves and droughts (e.g., 2003,2010,2013,2015,2018,2019), associated with substantial environmental damage and financial and human losses [9][10][11][12][13][14] . For example, the financial losses due to the 2018 drought were estimated to be~3.3 billion EUR, which made it the costliest single-year event in Europe 15 .…”

“…A similar non-stationary relationship between NAO and European precipitation was found by Vicente-Serrano and López-Moreno 25 . One possible reason for the non-stationary relationship between the European climate and predefined teleconnection indices might arise from the fact that these indices are defined based on sea level pressure or sea surface temperature data over a specific location 14 .…”