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Figure 5.5 Relationship between snow cover depletion and cumulative degree-days (CDD) at Kaza (3639 m) station

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© Observed SCA

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Figure 5.6 (a) Establishment of snow cover depletion trend for 1990 using cumulative degree-days (CDD) of Kalpa for the initial part of the summer. (b) Simulation of depletion of snow covered area (SCA) for the rest of summer using CDD data, and its comparison with observed SCA

Such a procedure is illustrated in Figures 5.6 and 5.7. The two unknowns (a and b) can easily be determined by plotting SCA on log scale and CDD on linear scale. This approach was applied for two years, 1990 and 1991, for simulating daily SCA in the study basin. Simulated SCA was compared with observed SCA in the later part of the melt season. As shown in Figure 5.6 and 5.7, for both years daily SCA was well simulated using this approach. The average error between observed and estimated SCA was about 6% and 8% for the year 1990 and 1991, respectively. The expected error can be further reduced if the data points used to parameterize the exponential curve

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Figure 5.7 (a) Establishment of snow cover depletion trend for 1991 using cumulative degree-days (CDD) of Kalpa for the initial part of the summer. (b) Simulation of depletion of snow covered area (SCA) for the rest of summer using CDD data, and its comparison with observed SCA

are increased. Error in predicting SCA will also depend on the error in predicting the CDD. Thus, following this approach, one can reduce the number of images for the later part of the season. However, for such applications, a setting of depletion trend with CDD is essential.

(c) Impact of climate change on SCA. Important impact of climate change is expected on the hydrological cycle and water management systems (Askew 1991). A temperature increase is expected in the next decades (Schneider 1989). Climate change effects on the hydrological behavior of snowfed rivers has been studied by various researchers (Rango 1992; Singh 1996; Singh and Kumar 1997). Singh and Kumar (1997) carried out detailed study on the effect of different climatic scenarios on different components of runoff for a highly snowfed river in the western Himalayas. Limited studies have been carried out to study the depletion of snow cover under the warmer climatic conditions. Rango and Martinec (1994) examined the influence of changes in temperature and precipitation on snow cover using snow melt runoff model (SRM).

In this study, depletion of SCA has been correlated with temperature, which enables studying the impact of warmer climatic scenarios on SCA. Effect of increase in temperature from 1 to 3°C has been studied on the depletion trend of SCA for the study basin. Depletion of SCA under different climatic scenarios for 1988 ablation period is shown in Figure 5.8. As expected, under warmer climate snow disappears from basin at faster rate, resulting in reduction in extent of SCA after melt season; extent of melting area during summer is increased under warmer climatic conditions. Similar trends were observed for all the years. Figure 5.9 shows that for all the years increase in melting area after the melt season was linearly correlated with increase in temperature. Because the initial SCA in the basin and distribution of temperature over the melt period vary from year to year, the impact of climate change would be different for different years. For the study basin, on average, an increase of temperature by 1,2, and 3°C increased the melting area by 2.7, 5.1, and 7.2%, respectively. Thus, following the present methodology, one can generate SCA in the basin under new climatic scenarios, which can be used as input to the modeling studies and other applications related to SCAs.

These results are based on the assumption that relationship between SCA and CDD does change under warmer climatic scenario. In fact, initial snow cover conditions and distribution of temperature govern the equation. Because initial snow cover itself will change under climatic conditions, equation between SCA and CDD may also change. Thus, results for the warmer climate may vary as given in this example.

5.7 CONCLUSIONS

Satellite-derived SCA is used for various hydrological and climatological studies. Such information is of practical significance in operational water resources

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