Download Impacts of Human Intervention and Climate Change on Water

Impacts of Human Intervention and Climate Change on Water Resources
H.P. Nachtnebel
IWHW-BOKU
[email protected]
Water resources systems are simultaneously exposed to direct human intervention and
impacts of possible climate change. The objective of this paper is to present a methodology to
discriminate among these different sources of impacts and to quantify the responses observed
in water resources systems. This analysis should assist in the development of revised
management practices and design principles of hydraulic structures.
Most of the simulations of the future climate are based on different emission scenarios of
greenhouse gases, dependent on different global economic and technological development
paths. In this study the A1B scenario is used that refers to a mix of a strong globally linked
technological development with social compatibility. It can be considered as an “optimistic
scenario” and it constitutes one of the key scenarios in the IPCC (2007) report. The scenario
simulations cover a long time period from which the period from 1960-1990, being called the
1*CO2 case, and the period from 2070-2100, which is named as the 2*CO2 case, are
compared. This terminology refers to the historic greenhouse gas concentration and a
doubling of total greenhouse concentration by the end of this century.
The climate models used in climate change studies are mostly based on a coarse spatial grid
each element covering several thousands of square kilometres. Only a few nested climate
simulations are available for Central and South Eastern Europe using a spatial resolution of a
few hundred square kilometres for a grid element. Therefore their outputs cannot be directly
used for local to regional impact studies and downscaling approaches are required to generate
local climate features and outputs, such as time series of daily precipitation and temperature.
Utilising these time series from different time periods, as indicated above, as an input to
hydrological models or to water management models the impacts can be studied at the
catchment scale to investigate the impacts on existing water management strategies. In a
similar way statistical estimates of quantiles are obtained for recent and future climate
conditions which provide the basis for design procedures.
Some recent investigations, such as the PRUDENCE and the CECILIA project, indicate that
climate change impacts will be regionally quite heterogeneous. Some general conclusions can
be drawn for Central and South-Eastern Europe. The temperature will go up until 2020 by
about 2,0 - 3,0 0C and annual rainfall seems to decrease in Southern Europe although different
models yield different and even contradicting outputs. Obviously these changes will have
severe impacts on water management strategies and the demand for enlarging irrigation areas
will pose new problems. Groundwater recharge is expected to decrease because of higher
evaporative losses and perhaps lower rainfall amounts. This implies that the drinking water
resources will be under increasing pressure and efficient water use will be an urgent task.
With respect to hydropower generation some studies conclude that the annual power
generation will stagnate or even decrease while the winter production might benefit due to an
increased runoff. All the statements about changes in the frequency of extremes are subjected
to large uncertainty. In Bavaria the design of levees has been already changed by adding a
15% climate change safety margin. The re-design of spillways of larger reservoirs is under
discussion and some countries have already started initiatives to enlarge the capacity of such
structures.