7997

• UCREFRP Catalog Number: 7997
• Author: Nash, L. L. and P. H. Gleick.
• Title: The Colorado River Basin and Climatic Change, The Sensitivity of Streamflow and Water Supply to Variations in Temperature and Precipitation.
• USFW Year: 1993.
• USFW - Doc Type: EPA 230-R-93-009,
• Copyright Material: NO

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Table 9: Changes in runoff generated by GCMs and the NWSRFS
hydrologic model

" Runoff (%)

GCM

NWSRFS

Equilibrium [1]

GISS 1
GISS2
GFDL

+20
+5
+5

+10
-8 to -14
-13 to -16

Transient [2]

GISS 1
GISS2

-5
+30

+4
+10 to +12

Noles: 11) Equilibrium GCM runs, in which greenhouse gas concentrations have stabilized at
roughly twice current levels.
12) The GISS transient run, in which greenhouse gases are increasing gradually. The
numbers presented here represenllhe avearge over the decade 2030 to 2039.

GCM Runoff Scenarios

GCM runoff scenarios are compared with the NWSRFS modeling results in Table 9. GCM

runoff predictions do not necessarily agree even in direction with those suggested by the hydrologic

modeling of GCM changes in temperature and precipitation. In the GISS equilibrium runs, runoff increases

by 20% at the more northern grid point (GISS 1) and by 5% at the more southern grid point (GISS 2).

Hydrologic modeling results that used the GISS temperature and precipitation inputs suggest that runoff

would increase by 10% in the White River basin (GISS 1) and decrease between 8 and 14% in the GISS 2

region. For the GFDL model, the runoff outputs indicate a increase of 5%, while hydrologic modeling

suggests runoff decreases between 16 and 23%. For the GISS transient scenario. GCM runoff decreases

by 5% at the more northern grid point. while the White River model suggests that equivalent temperature

and precipitation changes would result in a 4% increase in runoff. In the lower basin, represented by the

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