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Speaker: Sara Vassolo
s.vassolo<at>bgr.de
Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany
Title of the talk: Model-Based Scenarios of Drought in Europe (pdf: 13,5 Mb)
Summary of the talk by a student: Students´
summary (pdf)
Abstract
Model-based scenarios of droughts in Europe
Society generally considers floods as a much more relevant natural disaster than droughts. This may be due to the slow development of droughts as well as its less intensive although more prolonged effects, compared to the sudden and devastating effects of a flood. However, droughts regularly cause serious damage to humans, economies, societies, and environment not only in the directly affected regions but also further away. In the early 1990s, Europe experienced a prolonged period of severe drought with the ensuing economic and environmental costs. The damage in Spain, where the drought period lasted from 1990 to 1995 and affected mainly the southern half of the country, was estimated at several billion Euro. Also Italy, whose southern part was tremendously affected by a drought period between 1988 and 1990, recorded losses that summed up to several billion Euro. Presently, various regions in Europe (for example the northern Italy, and the Rhine and the Elbe basins in Germany) are suffering of drought, where almost no rainfall since beginning of the year 2003 have been experienced. Various studies conclude that the drought events in many European regions have worsened in the last decades, due to either an increase in frequency, duration, or intensity. And a further worsening as a result of climate change impacts is expected, particularly in the southern European regions.
Low flows and droughts generally cover large areas and extend for long periods of time, thus they should be investigated within a regional context using a spatially consistent methodology. In this paper, a comprehensive concept on how to analyse the impacts of global change (climate and socio-economic changes) on future low flow and hydrological drought frequencies on the European scale is presented. The aim of the paper is not to exactly quantify future droughts and low flow throughout Europe, but to answer the following question: in which European basin can we expect a significant increase of drought events or severity due to climate change? The analysis is based on the global integrated water model WaterGAP, which computes runoff and river discharge in a spatial resolution of 0.5º latitude by 0.5º longitude. The river discharge is directed along a river network based on a flow direction map. The model is also capable to calculate consumptive water use (fraction of withdrawal that is lost by evapotranspiration) in each cell, which is subtracted from the river discharge. Results are generally given at drainage basin or country scales. Therefore, WaterGAP is a spatially consistent methodology to arrive at comparable results throughout Europe.
The impact of climate change on droughts is analysed using two different global emission scenarios from the Intergovernmental Panel of Climate Change (IPCC), A2 and B2, such that a large range of possible future emissions is covered (Fig. 1). These emission scenarios are based on two scenarios of the future development of society. Scenario A2 assumes a strong economic growth, while B2 puts a stronger emphasis on the protection of the environment. Both scenarios represent a world in which the differences between developed and developing countries remain strong, and globalisation is restricted. Due to the uncertainties in the calculation of the precipitation of the global climate models, it is necessary to examine the results of at least two of them to illustrate the wide range of simulated precipitation changes. Here, we use the climate scenarios computed by the global climate models ECHAM4/OPYC3 (MPI for Meteorology, Hamburg) and HadCM3 (Hadley Center, UK) These models provide WaterGAP with changes in temperature and precipitation.
To complete the evaluation, the human impact on water resources must also be
investigated. This is done by means of water use scenarios, which are based
on assumptions for population growth and economic development that are consistent
to the IPCC scenarios A2 and B2 (Fig. 1). Here scenarios for 4 sectors of water
use are defined: households, industries, irrigation, and livestock.
As a result, both the change in magnitude of droughts and the change in frequency
of 100-year droughts throughout Europe, for the time slices 2020s and 2070s
(compared to the climate normal 1961-1990), is presented. Drought in this study
is defined as the lack of discharge to cover the water demand. The influence
of emission scenarios and applied climate models is discussed.
The main findings of this drought risk assessment, in which two different climate models and two different emission scenarios are combined, can be summarized as follows:
However, the limitations of drought risk analysis on a global scale should be kept in mind at the time of qualifying the presented findings. The calculations are inherently uncertain, as the involved processes are complex and difficult to predict, especially those anthropogenic influences (urbanisation, effluents, extractions) that affect the flow processes.
Animation of the development of the "Deficiency Index calculated by Water GAP 2.1" for Europe, Africa and the Near East from January 1961 to December 1990 (avi: 27MB)|
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