3.5. Future trends in virus concentrations considering climate
projections for the Mediterranean river catchment
The risk associated with waterborne viral infections would be
influenced by the exposure (concentration of virus in water) and
stability of the viruses in water. Thus, the temporal pattern and
population burden of several infectious diseases may shift and
human exposure may differ under future scenarios (Morse et al.,
2012). To study future trends in viral concentrations in the
selected river catchment, we generated climate projections to 2100
with the suite of climate models contained in the CMIP5þ project
database (see Methods). Due to the large uncertainty associated
with detailed spatial resolution simulations, a grid of 5 5 degrees
was preferred and applied. The results for the trend in the seasonality
of temperature and precipitation are presented in Fig. 4
together with the observed values for the same region derived
from the European Centre for Medium-Range Weather Forecasts
(ECMWF) interim re-analysis (ERA) (http://data-portal.ecmwf.int/
data/d/interim_daily/). A bias between current climate conditions
compared to those simulated with the ensemble of climate models
is clearly evident when compared to the observations (derived from
the ERA interim reanalysis). While it is true that there may be a
noticeable difference between station data and reanalysis fields for
a small region, we thought it convenient to highlight these disparities
to better define the scope of our study. Projections for
regional precipitation yield an estimate of a slight increase in total
amounts between the simulated winter months of 2070e2100 and
1980e2010 (on average approximately 1e3 mm/month) and
persistent decreases between May and October (on average
2.5 mm/month) (Fig. 4A). While these differences might be deemed
low, values rise considerably in relative terms when compared to
current observations (a general increase throughout the year with
localised maximum increases of approximately 30% in the main
winter months). Temperature projections for the region are presented
in Fig. 4B. In this case, systematic differences between observations
and simulations for the common 1980e2010 interval are
much lower than for the rainfall described above. The overall
change in temperature between the two intervals (2070e2100 vs
1980e2010) indicates a general warming trend throughout the
year, with an increase in the minimum winter temperatures that is
positive when compared to observations. Increases are above 13%
in summer months and approximately 11% in winter.
Globally, climate change is expected to shrink potable water
availability. In the Mediterranean climate regions it is predicted to
increase the intensity and/or frequency of floods and droughts.
Faecal contamination by means of viral concentrations may increase,
but at the same time environmental factors producing viral
inactivation could also increase in intensity. For example, UVB radiation
and the biotic activity indirectly associated with higher
temperatures (Carratala et al., 2013) could reduce viral viability,
compensating for the increasing viral loads. Where climate change
scenarios predict more frequent floods, the pollution events caused
by sewage overflows will increase, posing a challenge for water
managers. It is likely that the predicted reduction in the number of
summer rainfall events in the Mediterranean climate regions will
produce more frequent low river flows with greater proportions of
treated effluents entering surface water bodies, possibly increasing
viral pathogen concentrations in river water and the impacted
beaches (Figueras and Borrego, 2010; Cann et al., 2013).