Climate Change and the Hydrology and Morphology of Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 67

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Grassland Field Heather/peat Forest Urban Other

Figure 4.1 Land-use changes in the river Vecht catchment (the Netherlands) in a
period when climate change has been relatively minor.

present day, there has been only a minor change in climate. In contrast, there
have been major changes in land use and river morphology (canalization) taking
place simultaneously in the periods ±1895-1905, 1925-35 and 1955-65. The
area of heather and moorland peat decreased dramatically as agricultural, urban
and other human uses increased (Fig. 4.1).
The streams in the Vecht catchment show consequent degradation in structure
over the last 100 years. The total stream length was shortened by about 20%;
40% of the connected backwaters were lost; the number of oxbows increased in
the 1930s due to straightening of the major streams but has decreased since then,
with only 38% of the oxbows remaining. Over the last 100 years, an increase in
both temperature and precipitation has been observed, but average annual
discharge has not changed significantly over the last 30 years. In general, most
streams followed meandering channels in 1900; between 1930s and 1960s, some
were still meandering but currently most are straight.

Effects of climate change at the catchment scale

Direct climate impacts on stream hydrology
The effects that changes in climate may have on stream hydrology are illustrated
by the expected changes in discharge for the River Lambourn in southern England
(Fig. 4.2). The Lambourn catchment (265 km 2 ) has a limited river network owing
to its underlying porous chalk geology and is dominated by arable land and
improved pasture. Based on RCAO HadAM3H model outputs under the B2
scenario (see Chapter 3) and a catchment-scale rainfall-stream flow model