Geoscience Reference
In-Depth Information
studies of global and regional climate change, climate models are the current operational
tools. Although the ability of climate models to simulate the various characteristics of the
climate or Earth system has considerably improved within the past decades, gaps or large
uncertainties in the representation of some specific processes still exist. Consequently,
there is a lot of room for improvement. In the following, we will focus on climate-
hydrology interactions and provide two major perspectives for their modelling within the
framework of Earth system models (ESMs). Here, only those interactions that are relevant
on scales utilized in the current or forthcoming global and regional climate modelling
exercises are considered.
Harding et al. ( 2011 ) give a general overview of current knowledge of the terrestrial
global water cycle. Here, they consider aspects of state-of-the-art global hydrology mod-
elling, past and projected future hydrological change in means and extremes, as well as
uncertainties in our understanding of the current global water cycle and how it will develop
in the future. But in those aspects, the feedback of terrestrial hydrology to the climate is
mostly not considered. In order to investigate the interactions between climate and
hydrology and how they may behave under climate change conditions, a coupled frame-
work is necessary where both components are adequately represented. Strong interactions
between the climate, hydrology and land use occur (Claussen 2004 ; Falloon and Betts
2010 ). The snow-climate feedback is well known and described (e.g., Cess et al. 1991 ).
However, feedbacks between CO 2 , vegetation, soil moisture, groundwater recharge and
climate are less well understood and are not well described in most climate and hydro-
logical models.
Soil moisture controls the partitioning of the available energy into latent and sensible
heat flux and conditions the amount of surface runoff. By controlling evapotranspiration, it
is linking the energy, water and carbon fluxes (Koster et al. 2004 ; Dirmeyer et al. 2006 ;
Seneviratne and St ¨ckli 2008 ). Seneviratne et al. ( 2006 ) stated that a northward shift of
climatic regimes in Europe due to climate change will result in a new transitional climate
zone between dry and wet climates with strong land-atmosphere coupling in central and
eastern Europe. They specifically highlight the importance of soil-moisture-temperature
feedbacks (in addition to soil-moisture-precipitation feedbacks) for future climate changes
over this region. A comprehensive review of soil moisture feedbacks is given by
Seneviratne et al. ( 2010 ). Their general principles are known (e.g., Koster et al. 2004 ,
2006 ; Teuling et al. 2009 ), even though there is still room for model improvement.
Soil moisture shows a high variability from daily to interannual timescales. An
appropriate knowledge of soil moisture conditions is important for the initialization and
quality of seasonal to yearly climate predictions. Fischer et al. ( 2007 ) indicated that the
record-breaking European heat wave in 2003 was enhanced by the large soil moisture
anomalies that were caused by a large precipitation deficit together with early vegetation
green-up in the months preceding the extreme summer event. Loew et al. ( 2009 ) showed
that these soil moisture anomalies were observable using remote sensing sensors. Conse-
quently, the impact of soil moisture memory on the climate is an important scientific topic
(e.g., Seneviratne et al. 2006 ) and is addressed specifically in the BMBF project MiKlip
PastLand where its value for seasonal to decadal prediction is investigated.
From the hydrological perspective, two major challenges for modelling climate-
hydrology interactions have currently arisen where we will shed some light on in the
following. On a more short-term perspective, these comprise anthropogenic land use and
especially irrigation. The coupling of hydrology to carbon cycle and vegetation is
important on the long-term perspective, specifically the dynamics of permafrost and
wetlands.
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