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US. Globall Change e wear,::[° IPirogirarr
<br />46
<br />Trends in Peak Streamflow Timing
<br />Observed Tr nds
<br />1948 to 202
<br />q
<br />x&200 saw 0 1,0,46d Wboo
<br />-100 ealft, - 20d alt
<br />fid
<br />00" 20" 240' 260,
<br />Projected Trends
<br />by 2080, to 2099
<br />200, 220` 240" 260"
<br />Stewart et al 157
<br />Top map shows changes in runoff timing in snowmelt- driven streams
<br />from 1948 to 2002 with red circles indicating earlier runoff, and blue
<br />circles indicating later runoff. Bottom map shows projected changes
<br />in snowmelt- driven streams by 2080 -2099, compared to 1951 -1980,
<br />under a higher emissions scenario 91
<br />runoff, in some cases up to 60 days earlier. 157,159 For
<br />the Northeast, projections indicate spring runoff
<br />will advance by up to 14 days .151 Earlier runoff
<br />produces lower late - summer streamflows, which
<br />stress human and environmental systems through
<br />less water availability and higher water tempera -
<br />tures.145 Scientific analyses to determine the causes
<br />of recent changes in snowpack, runoff timing, and
<br />increased winter temperatures have attributed these
<br />changes to human - caused climate change .14,160,161
<br />Global Climate Change Impacts in the United States
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<br />Changes in water quality
<br />Increased air temperatures lead to higher water
<br />temperatures, which have already been detected in
<br />many streams, especially during low -flow periods.
<br />In lakes and reservoirs, higher water temperatures
<br />lead to longer periods of summer stratification
<br />(when surface and bottom waters do not mix).
<br />Dissolved oxygen is reduced in lakes, reservoirs,
<br />and rivers at higher temperatures. Oxygen is an
<br />essential resource for many living things, and its
<br />availability is reduced at higher temperatures both
<br />because the amount that can be dissolved in water
<br />is lower and because respiration rates of living
<br />things are higher. Low oxygen stresses aquatic
<br />animals such as coldwater fish and the insects and
<br />crustaceans on which they feed .14' Lower oxygen
<br />levels also decrease the self - purification capabili-
<br />ties of rivers.
<br />The negative effects of water pollution, includ-
<br />ing sediments, nitrogen from agriculture, disease
<br />pathogens, pesticides, herbicides, salt, and ther-
<br />mal pollution, will be amplified by observed and
<br />projected increases in precipitation intensity and
<br />longer periods when streamflows are 10w.146 The
<br />U.S. Environmental Protection Agency expects the
<br />number of waterways considered "impaired" by
<br />water pollution to increase .16' Heavy downpours
<br />lead to increased sediment in runoff and outbreaks
<br />of waterborne diseases .161,164 Increases in pollution
<br />carried to lakes, estuaries, and the coastal ocean,
<br />especially when coupled with increased tempera-
<br />ture, can result in blooms of harmful algae and
<br />bacteria. However, pollution has the potential
<br />of being diluted in regions that experience
<br />increased streamflow.
<br />Water - quality changes during the last century were
<br />probably due to causes other than climate change,
<br />primarily changes in pollutants .149
<br />Changes in groundwater
<br />Many parts of the United States are heavily de-
<br />pendent on groundwater for drinking, residential,
<br />and agricultural water supplies .164 How climate
<br />change will affect groundwater is not well known,
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<br />200, 220` 240" 260"
<br />Stewart et al 157
<br />Top map shows changes in runoff timing in snowmelt- driven streams
<br />from 1948 to 2002 with red circles indicating earlier runoff, and blue
<br />circles indicating later runoff. Bottom map shows projected changes
<br />in snowmelt- driven streams by 2080 -2099, compared to 1951 -1980,
<br />under a higher emissions scenario 91
<br />runoff, in some cases up to 60 days earlier. 157,159 For
<br />the Northeast, projections indicate spring runoff
<br />will advance by up to 14 days .151 Earlier runoff
<br />produces lower late - summer streamflows, which
<br />stress human and environmental systems through
<br />less water availability and higher water tempera -
<br />tures.145 Scientific analyses to determine the causes
<br />of recent changes in snowpack, runoff timing, and
<br />increased winter temperatures have attributed these
<br />changes to human - caused climate change .14,160,161
<br />Global Climate Change Impacts in the United States
<br />Srwurlauu: aut;rwur qua1ity auuriur°1111 giirwarwuuuiur °1111 aut;rwur
<br />qtjiaiinutity wflli Ill rw afft�ct( :NJ111 by au
<br />r: ulliauuriilgiiiuuriug r:n111iiiinaut;r .
<br />Changes in water quality
<br />Increased air temperatures lead to higher water
<br />temperatures, which have already been detected in
<br />many streams, especially during low -flow periods.
<br />In lakes and reservoirs, higher water temperatures
<br />lead to longer periods of summer stratification
<br />(when surface and bottom waters do not mix).
<br />Dissolved oxygen is reduced in lakes, reservoirs,
<br />and rivers at higher temperatures. Oxygen is an
<br />essential resource for many living things, and its
<br />availability is reduced at higher temperatures both
<br />because the amount that can be dissolved in water
<br />is lower and because respiration rates of living
<br />things are higher. Low oxygen stresses aquatic
<br />animals such as coldwater fish and the insects and
<br />crustaceans on which they feed .14' Lower oxygen
<br />levels also decrease the self - purification capabili-
<br />ties of rivers.
<br />The negative effects of water pollution, includ-
<br />ing sediments, nitrogen from agriculture, disease
<br />pathogens, pesticides, herbicides, salt, and ther-
<br />mal pollution, will be amplified by observed and
<br />projected increases in precipitation intensity and
<br />longer periods when streamflows are 10w.146 The
<br />U.S. Environmental Protection Agency expects the
<br />number of waterways considered "impaired" by
<br />water pollution to increase .16' Heavy downpours
<br />lead to increased sediment in runoff and outbreaks
<br />of waterborne diseases .161,164 Increases in pollution
<br />carried to lakes, estuaries, and the coastal ocean,
<br />especially when coupled with increased tempera-
<br />ture, can result in blooms of harmful algae and
<br />bacteria. However, pollution has the potential
<br />of being diluted in regions that experience
<br />increased streamflow.
<br />Water - quality changes during the last century were
<br />probably due to causes other than climate change,
<br />primarily changes in pollutants .149
<br />Changes in groundwater
<br />Many parts of the United States are heavily de-
<br />pendent on groundwater for drinking, residential,
<br />and agricultural water supplies .164 How climate
<br />change will affect groundwater is not well known,
<br />
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