|Martinec, Jaroslav - CONSULTING HYDROLOGIST|
Submitted to: Hydrological Sciences Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 1999
Publication Date: April 1, 2000
Interpretive Summary: Assessing the future hydrologic effects of climate change with calibrated hydrologic models is problematic because they cannot be calibrated for a future climate. Additionally, different watersheds in different climates will respond uniquely to a climate change. The noncalibrated Snowmelt Runoff Model (SRM) was used to evaluate the response of three different snowmelt basins in different climate zones to an increase in temperature and a subsequent decrease in snow cover. In response to a 4 degrees Centigrade warming winter, runoff is as much as doubled at the expense of summer runoff, and the decline of snow covered area is accelerated by about one month in all basins. The Kings River basin in California experiences the greatest decline in snowpack. The Rio Grande in Colorado is the coldest basin so that the effect of warmer temperatures is not so pronounced on winter streamflow. There is an annual runoff increase in the eIllecillewaet basin in British Columbia due to enhanced glacier melt. The results of this study, which shows the merits of using noncalibrated hydrologic models, should be valuable to Federal water resource agencies (such as NRCS), state water agencies, hydropower companies, and irrigation districts.
Technical Abstract: The effect of a hypothetical temperature increase of +4 degrees Centigrade on snow cover and on year-round runoff is evaluated for the very humid basin Illecillewaet (1155 square km, 509-3150 m a.s.l., British Columbia, Canada), the semi-humid basin of Kings River (3999 square km, 171-4341 m a.s.l., California,USA), and the semi-arid basin of Rio Grande at Del Norte e(3419 square km, 2432-4215 m a.s.l., Colorado, USA). In contrast to current methods of evaluating the climate effect, a realistic seasonal snow cover from satellite monitoring is used to represent the present climate. The noncalibrated SRM model is applied to transform this snow cover under conditions of a warmer climate and to compute the climate-affected runoff. The winter snow accumulation is particularly reduced in the Kings River basin which has the greatest elevation range. In absolute terms, the smallest snowpack reduction occurred in the semi-arid basin of Rio Grande at Del Norte. The decline of snow covered area in the snowmelt season in accelerated by about one month in all basins. The runoff in the winter half year is about doubled at the expense of the summer half year in the basins of Illecillewaet and Kings River. This effect is smaller in the basin of Rio Grande at Del Norte. Because the climate change was limited to a temperature increase, there is no significant change in the yearly runoff volume in the basins of Kings River and Rio Grande. There is a yearly runoff increase in the Illecillewaet basin due to enhanced glacier melt.