T.C. Orman ve Su İşleri Bakanlığı

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Assessment of Climate Change Impacts on Snowmelt and Streamflows of Mountain Region in Eastern Turkey

Introduction

     Climate change causes snow cover to shrink, land and sea ice to melt, sea level to rise, climatic zones to shift, more severe weather events and floods to occur and their impacts to strengthen, and drought, erosion, desertification, epidemic illnesses, and agricultural pests to spread, and thus, it is foreseen that there will be significant consequences of these on human life and health, socioeconomic sectors and ecological systems (IPCC, 2001). 

     Snow cover reduction as a result of climate change could have adverse impacts particularly on the water resources of the snow-fed river basins. Significant portion of the annual runoff comes from snowmelts in Euphrates Basin, which has the highest water potential among Turkey’s rivers. Besides, the basin mainly covers most of the Eastern and Southeastern Anatolia regions.The aim of the "Assessment of Climate Change Impacts on Snowmelt And Streamflows Project" is to assess the effects of climate change on snow loads and its melting and consequently the changes in streamflow in Upper Euphrates Basin for the period of 2020 - 2100. In order to generate the predictions of the climate change effect on the area, projected temperature and precipitation data is gathered from  "Impacts of Climate Change on Water Resources Project" which is conducted to determine the climate scenarios and alterations in the water budget.

     Within the project;
  • Snow observation data will be collected,
  • Naturalized daily streamflows will be estimated,
  • Snow cover characterization will be determined,
  • Snow depletion curves will be generated using satellite images,
  • MPI-ESM-MR general circulation model outputs for RCP4.5 and RCP8.5 scenariosfor the years 2020-2100 were used to project:
  • - Snow-covered areas,
  • - Snow-water equivalent,
  • - Runoff caused by snowmelt,
  • - Projections of snowmelt-induced peak discharge timing and shifts,
  • - Projections of the amount of low-flow period flow and their temporal projections.
Upper Euphrates Basin and Sub-basins

Climate of the Region

The measurements of 154 meteorological observation stations, 111 snow observation stations and 54 discharge observation stations were used in this project.

The climate characterization of the basin for 1971-2000 reference period was determined. Accordingly, the average temperature of the Upper Euphrates Basin is 9.5°C, where the total rainfall is 569 mm. In addition, the average of snow depth and snow water equivalent of the basin for December, January, February and March are found as 40 cm and 11 cm, respectively.

Snow Characterization Process of the Project

     Snow cover characterization of the region is determined by assessing the information such as satellite images, the historical minimum snow elevation, snow depth-altitude relationship, and snow-water equivalence for each subbasin.

    Minimum, average and maximum daily basis snow covered area graphics are prepared by utilizing MODIS and IMS satellite products for Karasu subbasin are given in Figure 1.
 
Figure 1. Karasu Subbasin Snow Depletion Curve

Table 1. Karasu Subbasin Number of Days Specific to Snow Covered Area Analysis

Karasu Subbasin
 
Minimum Mean Maximum
≥ 75% SCA 03 Jan - 05 Mar
(62 Days)
10 Dec - 27 Mar
(108 Days)
21 Oct - 25 Apr
(187 Days)
≥ 50% SCA 23 Dec - 09 Mar
(77 Days)
30 Nov - 09 Apr
(131 Days)
21 Oct - 30 Apr
(192 Days)
≥ 25% SCA 16 Dec - 01 Apr
(107 Days)
09 Nov - 27 Apr
(170 Days)
20 Oct - 11 May
(204 Days)

     In Table 1, 25%, 50% and 75% snow covered areas (SCA) are observed by satellite of Karasu subbasin for long-term period gives the number of days accordingly.

Within the project, snow characterization of the basin for December, January, February and March was carried out by the analysis of snow depth, snow water equivalent, snow density, snow line, and number of days covered with snow using historical snow data (1970-2016).

Snow depth and snow water equivalent values reach to maximum levels in March, where are away from the influence of urbanization. It was observed that snow density increases from December to March and reaches the maximum levels in March.



Figure 2. Average of SWE, SD and Density

Future Projection 

The changes throughout the projection period related to deviations from reference period (anomalies) were calculated for the parameters of snow-covered area, snow water equivalent and surface runoff.


Climate Projections

In the Upper Euphrates basin, mean temperature is estimated to increase gradually by the end of the century and to rise up to 4.5 °C in the last 30-years period. Furthermore, precipitation simulations indicate a decrease up to 7% in the downstream basins for the same projection period.




Figure 3. Anomaly Changes of Temperature (above) and Precipitation (below) for (2020-2100) - (1971-2000)

In the future period, it is estimated that the Upper Euphrates Basin will be fed by mainly rainfall rather than snow cause by increasing temperature.

Projection of Snow Covered Areas

The percentage of snow-covered area and the number of snow-covered days will decrease in all sub-basins for each period.


Figure 4. SCA Changes under RCP8.5 Scenario in 2071-2100 period

Particularly in the last 30-years of the century, a reduction up to 44% in snow-covered area has been predicted in high elevated regions. Furthermore, snow accumulation and melting periods have been estimated to shorten.

It is predicted that the number of days where the snow-covered area is above 50% will decrease by 25 days in the upstream sub-basins and a decrease of 50 days in the downstream sub-basins.


Figure 5. SC Day Changes under RCP8.5 Scenario in 2071-2100 according to 1971-2000

Snow Water Equivalent Projection 

The Snow Water Equivalent, which represents the total water content of the snow cover, is estimated to decrease by 44% in the upstream basins of Upper Euphrates Sub-Basins (Karasu 1, Karasu 2, Murat 1, Murat 2 Sub-Basins), a decrease of 54% in Karasu 3, Munzur and Peri Sub-Basins and a decrease of 63% is foreseen in Murat 3 and Çaltı Sub-Basins. Ara Havza which is located in the downstream is projected to decline by 67%.


Figure 6. SWE Changes under RCP8.5 Scenario in 2071-2100 period

Projections also show that snow water equivalent reaches peak levels around March and snow melt starts earlier due to the temperature increase .

Surface Runoff Projection 

The surface runoff of sub-basins are estimated to decrease by 8% to 12% for Murat 1, Murat 2 and Murat 3, by 5% for Munzur Suyu and Peri Suyu, by 9% to 20% for Çaltı Suyu, and up to 12% for Ara Havza in the projection period of 2071-2100.

Figure 7. Surface Runoff Changes under RCP8.5 Scenario in 2071-2100 period

The dates that total runoff passes the center of time (50%) in the projection period of 2071-2100, the time shifts are estimated to move 10 days earlier for Karasu Çayı Sub-Basins, 13 days earlier for Munzur Suyu, 15 days earlier for Çaltı Suyu, and up to 14 days earlier for Murat Çayı Sub-Basins.


Figure 8. Number of Lagged Days during Melting Period Under RCP8.5 Scenario in 2071-2100

During the melting period, the total runoff is predicted to decrease by 8% in the projection period compare to reference period in the Upper Euphrates Basin.

Conclusion

In the Euphrates Sub-Basin, where snowfall is crucial source of water, the predicted temperature increases and the streamflow decreases will adversely affect the water intensive sectors throughout to century.

Because of the shifts in snow line towards the higher altitude, both snow-covered area and water volume is projected to decrease. These changes are expected to damage the winter tourism sector the most.

As a result of the effects of climate change on the snow cover, it is predicted that changes in flora and fauna in the ecosystem might have a harmful affect on all human-centered systems.

Changes in snow potential and the runoff regime may have negative effects on water management in terms of flood control, irrigation, and energy production. In order to deal with those results, reservoir operation strategies may need to be revised and improved to adapt to the adverse consequences of climate change.

>> Executive Summary of "Assesment of Climate Change Impact on Snowmelt and Steamflows Project's Final Report" will be published soon.

Further Readings:

>> Previous study of the department which is; Impact of Climate Change on Water Resources Project:

 

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