Page 97 - Climate Change and Food Systems

adaptation interventions will involve water resource management.
Bates et al.(2008) summarizes the interactions of climate change with water. Observed warming over recent decades has been linked to changes in the large-scale hydrological cycle, including increasing atmospheric water vapor content; changing precipitation patterns, intensity and extremes; reduced snow cover and widespread melting of ice; and changes in soil moisture
and runoff. Over the 20th century, precipitation
has mostly increased over land in high northern latitudes, while decreases have dominated from 10°S to 30°N since the 1970s. Globally, dry land has doubled since the 1970s and water storage in mountain glaciers significantly contracted. Climate model simulations for the 21st century consistently show precipitation annual average river runoff
and water availability increases in high latitudes and parts of the tropics, and decreases in some subtropical and lower mid-latitude regions. Outside these areas, there remains substantial uncertainty in precipitation projections.
Increased precipitation intensity and variability are projected to increase the risks of flooding and drought, while water supplies stored in glaciers and snow cover are projected to decline, thus reducing water availability during warm and dry periods in regions supplied by melt water from major mountain ranges. Higher water temperatures and changes in extremes, including floods and droughts, are projected to affect water quality and exacerbate water pollution. In addition, sea-level rise is projected to extend areas of salinization
of groundwater and estuaries, resulting in a decrease in available freshwater for humans and ecosystems in coastal areas. By the 2050s, the area of land subject to increasing water stress due to climate change is projected to be more than double that with decreasing water stress. While quantitative projections of changes in precipitation, river flows and water levels at the river-basin scale are uncertain, it is very likely that hydrological characteristics will change in the future.
There is well-established literature describing the hydrological processes and their links to
climate change. Watershed and macro-scale hydrological models describe the effects of projected changes in precipitation, temperatures and evapotranspiration on water runoff and stream flow, taking into account the moisture-holding capacity of soils. Some IAMs are beginning to incorporate water into their analyses. Since water management is fairly localized, it raises important issues of scale in relation to global hydrological cycles and a major challenge in linking climatic to hydrologic processes shaping water resources (Bell et al., 2014). The gap between GCMs and
the needs of hydrological models can be filled through downscaling (Benestad, 2010). Still the challenge of data remains, as the information required to develop water management data inputs to IAMs typically lies with local water management institutions, posing challenges for thorough and consistent data collection (Olmstead, 2013).
Hydrology model results are used in economic assessments of climate change to describe the effects of water stress on crop yields, the effects of floods on road infrastructure, changes in irrigated crop area, and changes in the stream flow used for hydropower and irrigated water supply. McCluskey and Qaddumi (2011), and Strzepak and McClusky (2010) provide useful overviews of three types
of hydrological models used to produce these results for economic analyses. Firstly, there are the distributed and gridded models, which describe water run-off at small spatial scales, and can
take into account variations among spatial grids
in soil qualities and topography. Second are the watershed or water basin models that describe water runoff that occurs over the entire basin area, without describing any interior spatial variations. Third, macro-scale hydrological models simulate runoff and stream flow at very large scales
of continents or large river basins. Projected hydrological impacts are derived by using the models to simulate the results from GCMs for future changes in temperature and precipitation.
Still, hydrologic modelling is not a necessary starting point for any model to study climate– water interactions, as relevant climate and water processes can be represented by bounding
chapter 3: economic modelling of climate impacts and adaptation in agriculture: a survey of methods, results and gaps
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