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Sayedi, Sayedeh Sara ¹ ; Malekmohammadi, Bahram ² ; Ghandehari, Mehran³

¹ Graduate Faculty of Environment, University of Tehran, Tehran, Iran
² Graduate Faculty of Environment, University of Tehran, Tehran, Iran
³ Department of Geography, University of Colorado-Boulder, Colorado, USA

Humans benefit from the ecosystems in many ways (Millenium Ecosystem Assessment, 2005). Hydrological ecosystem services (HES), i.e., water supply services, are one of the most important ecosystem services and have a significant role in people’s lives. These services have tremendously diminished in the Zayanderood Watershed, which contains the largest river of the Iranian Plateau in central Iran. Changes in climate (precipitation and temperature) and land use have noticeable impacts on the HES. It has been predicted that at the end of the current century, climate change will be the most important driving force of changing ecosystem services (Millenium Ecosystem Assessment, 2005). In this research, the HES is modeled using different hypothetical future climate and land use scenarios. It provides policy makers and managers with water-efficient land management strategies and the best possible information about critical HES issues, as well as future water yield estimates for the Zayanderood Watershed.

This research examined the scenarios of future climate change reported by the Intergovernmental Panel on Climate Change (IPCC) (Carter et al., 2007). Two scenarios A2, and B1 were chosen in this research. In the IPCC’s report, these scenarios are considered as the worst and best case predictions of future climate change, respectively. These scenarios have been defined based upon the assumptions about future technological and economic development. The InVEST (integrated valuation of ecosystem services and tradeoffs) water model was selected for modeling water yield. Models were run for the year 2007 as a benchmark, and a comparison basis for future predictions. The year 2040 were chose for predictions as the ministry of energy of Iran set its long-term goals to meet by this year. Precipitation and temperature are considered the driving forces on the watershed systems. To achieve the best water yield considering these forces, several land use scenarios for the future of the Zayanderood watershed were defined: the continuation of current trend, the development with protection, economic development, and natural resources protection and restoration.

This model was run for the two climate scenarios and the four land use scenarios. Then the results of water yield for the entire watershed and the sub-watersheds were investigated and compared. The results revealed that less water would be supplied by the Zayandehrood watershed due to climate changes, and this reduction is higher for the A2 scenario than the B1 scenario. In addition, the water yield is greatest when the natural resources protection and restoration’s scenario was employed. After dividing the watershed into the upper- and lower- divisions of the Zayandehrood dam, it was concluded that sub-watersheds in the lower division are more sensitive to climate changes. Although the upper division sub-watersheds are less sensitive to climate changes, they are more sensitive to land use changes.

Carter, T.R., Hulme, M. and Lal, M., 2007, General guidelines on the use of scenario data for climate impact and adaptation assessment: Intergovernmental Panel on Climate Change, Version 2

Millennium Ecosystem Assessment (MA), 2005, Ecosystems and Human Well-Being: Synthesis: Island Press, Washington, 155pp