Jökull - 01.01.2013, Blaðsíða 71

Reviewed research article
Sensitivity of Icelandic river basins to recent climate variations
Philippe Crochet
Icelandic Meteorological Office, Bústaðavegur 9, IS-150 Reykjavík, Iceland
Corresponding author: philippe@vedur.is
Abstract – Variations in 22 hydrological variables were considered for 8 watersheds in Iceland to analyse the
quantitative impact of variations in climate on hydrology during the period 1971–2006. Observed streamflow
characteristics were examined together with information about rain/snow fraction, snow storage, snow and
glacier melting derived from gridded precipitation and temperature data using a simple temperature-index melt
model. The effect of the observed temperature and precipitation variations was examined by comparing subsets
of the data containing the 25% coldest and warmest and the 25% wettest and driest years of each series. The
seasonality of streamflow of all catchments and timing of hydrological events were found to be sensitive to
differences of 1.1–1.4 ◦C in the annual temperature between the warm and cold data subsets. Snow storage
was smaller and depleted earlier and the onset of spring snowmelt was shifted several weeks earlier in warm
years, while glacial melt volumes increased by 20–40%. These changes caused greater discharge in winter and
spring and less discharge in summer, except for glacierized catchments where summer flow was maintained
by glacier melt. Annual precipitation was 40–58% greater in the wet compared with the dry data subsets,
resulting in substantial seasonal and annual increases of rain, snow storage and snowmelt, streamflow volumes
and flood occurrence rate. The seasonal distribution and timing of hydrological events were, however, usually
not systematically different. Snow storage and glaciers are found to exert a strong influence on streamflow
in Icelandic river catchments, making them sensitive to climate variations. The nature of the hydrological
response is not spatially uniform but depends on location, altitude distribution and catchment type.
INTRODUCTION
The impact that climate changes may induce on hy-
drological processes and water resources has been of
growing concern in various parts of the world. Ex-
amples of climate impact studies include analysis of
historical hydrological time series (Westmacott and
Burn, 1997; Robson et al., 1998; Whitfield, 2001;
Burn and Hag Elnur, 2002; Labat et al., 2004; Lind-
ström and Bergström, 2004; Zhang et al., 2005, 2006;
Hannaford and Marsh, 2008; Peterson et al., 2008;
Jónsdóttir et al., 2006, 2008; Wang et al., 2008; Jóns-
dóttir and Uvo, 2009; Kumar et al., 2009; Petrow
and Merz, 2009; Stahl et al., 2010; Wilson et al.,
2010) and hydrological simulations based on future
climate scenarios (Dettinger et al., 2004; Stewart et
al., 2004; Dankers and Christensen, 2005; Beldring et
al., 2006; Bergström et al., 2007; Fowler and Kilsby
2007; Hagg et al., 2007; Huss et al., 2008; Leander et
al., 2008; BACC author team, 2008; López-Moreno
et al., 2009). These studies, and many others, show
that climate variations and changes, either natural or
human induced, influence various aspects of the hy-
drological cycle.
In many mountain and high latitude regions,
snow-covered areas and glaciers exert a strong influ-
ence on runoff generation and seasonal runoff dis-
tribution by storing and releasing water over a wide
range of time scales (Jansson et al., 2003). For some
watersheds, glaciers, in particular, provide a buffer-
ing effect on streamflow and act as stream regulators
(Young, 2009). These hydrological systems are par-
ticularly sensitive to climate variations as snow and
ice respond quickly to variations in temperature and
precipitation.
JÖKULL No. 63, 2013 71