EFFECTS OF CLIMATE-CHANGE ON INLAND WATERS OF THE PACIFIC COASTAL MOUNTAINS AND WESTERN GREAT-BASIN OF NORTH-AMERICA

The region designated as the Pacific Coastal Mountains and Western Gre at Basin extends from southern Alaska (64 degrees N) to southern Calif ornia (34 degrees N) and ranges in altitude from sea level to 6200 m. Orographic effects combine with moisture-laden frontal systems origina ting in the Pacific Ocean to produce areas of very high precipitation on western slopes and dry basins of internal drainage on eastern hanks of the mountains. In the southern half of the region most of the runo ff occurs during winter or spring, while in the northern part most occ urs in summer, especially in glaciated basins, Analyses of long-term c limatic and hydrological records, combined with palaeoclimatic reconst ructions and simulations of future climates, are used as the basis for likely scenarios of climatic variations. The predicted hydrological r esponse in northern California to a climate with doubled CO2 and highe r temperatures is a decrease in the amount of precipitation falling as snow, and substantially increased runoff during winter and less in la te spring and summer. One consequence of the predicted earlier runoff is higher salinity in summer and autumn in San Francisco Bay. In salin e lakes, the incidence of meromixis and the associated reduction in nu trient supply and algal abundance is expected to vary significantly as runoff fluctuates. In subalpine lakes, global warming will probably w ill lead to increased productivity. Lacustrine productivity can also b e altered by changes in wind regimes, drought-enhanced forest fires an d maximal or minimal snowpacks associated with atmospheric anomalies s uch as Fl Nino-Southern Oscillation (ENSO) events. Reduced stream temp erature from increased contributions of glacial meltwater and decrease d channel stability from changed runoff patterns and altered sediment loads has the potential to reduce the diversity of zoobenthic communit ies in predominately glacier-fed rivers. Climatic warming is likely to result in reduced growth and survival of sockeye salmon in freshwater , which would, in turn, increase marine mortality. Further research ac tivities should include expanded studies at high elevations and of gla cier mass balances and glacial runoff, applications of remote sensing to monitor changes, further refinement of regional climatic models to improve forecasts of future conditions and continued analyses of long- term physical, chemical and biological data to help understand respons es to future climates. (C) 1997 by John Wiley & Sons, Ltd.