WATER QUANTITY AND FLOW CHANGES
Although precipitation is one of the main factors determining water availability and
flow, other factors such as evaporation, soil moisture, groundwater recharge, and glacial
and snowmelt are also critical. Evaporation is generally expected to increase due to increasing
mean temperatures. However, the exact amount of evaporation that will occur
at a given site is determined by a host of other factors, including soil characteristics, the
amount of water available, vegetation cover, and plant transpiration (which is affected
by temperature and atmospheric carbon dioxide concentrations; Arnell et al., 2001). Soil
moisture will depend on soil characteristics and the magnitude of local precipitation
changes, and soil infiltration and water-holding capacity will in turn determine the volume
of run-off. For example, drier soils often shows reduced water infiltration, and less
extreme freezing events can reduce water infiltration in limestone soils (Boix-Fayos et
al., 1998); reduced water infiltration could lead to greater run-off and an increase in
flooding events. Groundwater recharge is affected by both the amount of precipitation
and the duration of the recharge season, as well as by evaporation and soil moisture (Arnell
et al., 2001). Although climate change is likely to lead to some changes in groundwater
recharge, freshwater ecosystems that primarily receive input from groundwater
are likely to experience smaller changes in water temperature and quantity than those
dominated by precipitation