River flow drought

Change in the severity of river flow droughts in Europe 1962-1990

Note: The map shows change in the severity of river droughts

Data source:

Hisdal, H.; Stahl, K.; Tallaksen, L. M. and Demuth, S., 2001. Have droughts in Europe become more severe or frequent? International Journal of Climatology 21: 317333.

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Change in the severity of river flow droughts in France 1960-2000

Note:

Data source:

Lang, M.; Renard, B.; Sauquet, E.; Bois, P.; Dupeyrat, A.; Laurent, C.; Mestre, O.; Niel, H.; Neppel, L. and Gailhard, J., 2006. Climate Variability and Change Hydrological Impacts. IAHS Publ. 308.

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Projected change in mean annual and summer minimum 7-day river flow between 2071-2100 and the reference period 1961-1990

Note: Red indicates more severe droughts, blue less severe droughts

Data source:

Feyen, L. and Dankers, R., 2008. River flow drought in Europe in a future climate. Manuscript submitted to Global Environmental Change.

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Past trends

Over the past 30 years, Europe has been affected by a number of major droughts, most notably in 1976, 1989, 1991, and more recently, the prolonged drought over large parts of the continent associated with the 2003 summer heatwave. The most serious drought in the Iberian Peninsula in 60 years occurred in 2005, reducing overall EU cereal yields by an estimated 10 %. The drought also triggered forest fires, killing 15 people and destroying 180 000 ha of forest and farmland in Portugal alone (UNEP, 2006). However, there is no evidence that river flow droughts have become more severe or frequent over Europe in general in recent decades (Hisdal et al., 2001), nor is there conclusive proof of a general increase in summer dryness in Europe over the past 50 years due to reduced summer moisture availability (van der Schrier et al., 2006).
Despite the absence of a general trend in Europe, there have been distinct regional differences. In particular, more severe river flow droughts have been observed in Spain, the eastern part of eastern Europe and large parts of the United Kingdom (Hisdal et al., 2001). However, in the United   Kingdom there is no evidence of a significant increase in the frequency of occurrence of low river flows (Hanneford and Marsh, 2006). In large parts of central Europe and in the western parts of eastern Europe droughts have become less severe (Hisdal et al., 2001). In France, a majority of stations showed a decreasing trend in the annual minima of 30-day mean river flows over the past 40 years, but no such trend was found for drought severity or duration (Lang et al., 2006). In southern and eastern Norway there has been a tendency towards more severe summer droughts (Hisdal et al., 2001). On the other hand, several stations in Europe have shown trends towards less severe low flows over the 20th century, consistent with an increasing number of reservoirs becoming operational in the catchments over the period for which there are records (Svensson et al., 2005).

Projections

River flow droughts are projected to increase in frequency and severity in southern and south-eastern Europe, the United Kingdom, France, Benelux, and western parts of Germany over the coming decades. In snow-dominated regions, where droughts typically occur in winter, river flow droughts are projected to become less severe because a lower fraction of precipitation will fall as snow in warmer winters. In most of Europe, the projected decrease in summer precipitation, accompanied by rising temperatures which enhances evaporative demand, may lead to more frequent and intense summer droughts (Douville et al., 2002; Lehner et al., 2006; Feyen and Dankers, 2008). As a result of both climate change and increasing water withdrawals, more river basins will be affected by severe water stress, resulting in increased competition for water resources. The regions most prone to an increase in drought risk are the Mediterranean and south-eastern parts of Europe, which already suffer most from water stress (Alcamo et al., 2003; Schroter et al., 2005).