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<br />hydrologic evaluations need to incorporate the complexities of snowfall and snowmelt, topography, soil <br /> <br />characteristics, natural and artificial storage, and monthly or seasonal variations. <br /> <br />Table 2: Changes in temperature and precipitation in the Colorado River <br />Basin predicted by general circulation models (GCMs). [1] <br /> <br />t:. Temperature (oC) <br /> <br />t:. Precipitation (0/0) <br /> <br />Equilibrium [2] <br /> <br />GISS 1 <br />GISS2 <br />GFDL <br />UKMO 1 <br />UKMO 2 <br /> <br />+4.8 <br />+4.9 <br />+4.7 <br />+6.8 <br />+6.9 <br /> <br />+20 <br />+10 <br />o <br />+30 <br />+10 <br /> <br />Transient [3] <br /> <br />GISS 1 <br />GISS2 <br /> <br />+3.2 <br />+2.5 <br /> <br />+10 <br />+20 <br /> <br />Notes: (1) For the GISS and UKMO GCMs. the upper Colorado River basin was intereseoted by two <br />different grid points. The more northern grid point is labeled "1"; the more southern is labeled "2". <br />(2] Equilibrium GCM runs. In whloh greenhouse gas oonoentrations have stabilized at roughly twioe <br />ourrent levels. <br />(3) The GISS transient run. In whioh greenhouse gases are Inoreasing gradually. The numbers <br />presented here represent the avearge over the deoade 2030 to 2039. <br /> <br />The use of hydrologic models, rather than GCMs, for assessing the regional Impacts of climatic <br /> <br />changes has several attractive characteristics. First, diverse modeling techniques exist. This permits <br /> <br />flexibility In identifying and choosing the most appropriate approach for evaluating any specific region. <br />Second, hydrologic models can be chosen to fit the characteristics of the availabfe data. Third, hydrologic <br /> <br />models are regional In scale and are far easier to manipulate and modify than are GCMs. Fourth, regional <br /> <br />models can be used to evaluate the sensitivity of specific watersheds to both hypothetical changes In climate <br />and to changes predicted by large-scale GCMs or climatic analogues. And finally. methods that Incorporate <br />both detailed regional characteristics and output from GCMs can take advantage of the continuing <br />Improvements In the resolution. regional geography, and hydrology of global climate models (Glelck. 1989). <br /> <br />10 <br />