Attribution analysis for water yield service based on the geographical detector method:A case study of the Hengduan Mountain region

Ecosystem services,which include water yield services,have been incorporated into decision processes of regional land use planning and sustainable development.Spatial pattern characteristics and identification of factors that influence water yield are the basis for decision making.However,there are limited studies on the driving mechanisms that affect the spatial heterogeneity of ecosystem services.In this study,we used the Hengduan Mountain region in southwest China,with obvious spatial heterogeneity,as the research site.The water yield module in the InVEST software was used to simulate the spatial distribution of water yield.Also,quantitative attribution analysis was conducted for various geomorphological and climatic zones in the Hengduan Mountain region by using the geographical detector method.Influencing factors,such as climate,topography,soil,vegetation type,and land use type and pattern,were taken into consideration for this analysis.Four key findings were obtained.First,water yield spatial heterogeneity is influenced most by climate-related factors,where precipitation and evapotranspiration are the dominant factors.Second,the relative importance of each impact factor to the water yield heterogeneity differs significantly by geomorphological and climatic zones.In flat areas,the influence of evapotranspiration is higher than that of precipitation.As relief increases,the importance of precipitation increases and eventually,it becomes the most influential factor.Evapotranspiration is the most influential factor in a plateau climate zone,while in the mid-subtropical zone,precipitation is the main controlling factor.Third,land use type is also an important driving force in flat areas.Thus,more attention should be paid to urbanization and land use planning,which involves land use changes,to mitigate the impact on water yield spatial pattern.The fourth finding was that a risk detector showed that Primarosol and Anthropogenic soil areas,shrub areas,and areas with slope<5°and 250-350 should be recognized as water yield important zones,while the corresponding elevation values are different among different geomorphological and climatic zones.Therefore,the spatial heterogeneity and influencing factors in different zones should be fully con-sidered while planning the maintenance and protection of water yield services in the Hengduan Mountain region.

Spatially-explicit quantitative relationship for a potential PES mechanism:Cascade hydropower development in Yarlung Zangbo River Basin, China

Payment for ecosystem services(PES) is of great importance for the sustainable development of mountain areas, key hotspot regions for the provisioning of ecosystem services. At present, PES researches mainly focus on forest protection, carbon sink trading, and water protection. As an important industry in mountainous areas, cascade hydropower development has generated substantial economic benefits accompanied by social and ecological impacts. However, efficient PES mechanisms to deal with hydropower generation in mountain areas are still unavailable. Therefore, the lacking of PES in mountain systems limits the development of those areas, and compromise the sustainability of hydropower development. The critical reason lies in the lack of a scientific method that can quantitatively analyze the relationship of hydropower stations with a geographical scope at county level(i.e., quantifying the water yield service provided by each county within the cascade hydropower development basin), and with different hydropower enterprises. We use the Yarlung Zangbo River Basin of China as case study area, one of the major hydropower development basins in China. First, we used Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST) model to map water yield service. Then, we calculated the value of water yield service by relating the water yield to the gross output value of hydropower stations. We revealed the relationship(e.g., hydropower stations and identified counties) between the payers and the payees of ecosystem services through mapping and quantifying the provisioning regions in the supply of water yield service and the users(hydropower enterprises). Finally, we discussed the current situation of benefit distribution in cascade hydropower development basin based on the supply and use of the water yield service. The results showed that 1) the spatial distribution of the value of water yield service is uneven: the upper reaches are highvalue areas;the eastern region is higher than the western region;and the maximum value(USD 119.2$/km2) is 34 times higher than the minimum value(USD 3.5 $/km2). 2) We found that four state-owned enterprises are the direct beneficiaries of water yield service, and 37 counties are suppliers, among which Gongbogyamda, Lhari and Damxung are the first level of supply. 3) Each hydropower station is provided with water yield service by several counties, and the value of water yield service varies greatly in each county, showing spatial differences. 4) Most counties are only partially involved in the process of water yield service being used by hydropower stations(i.e.,the boundary of water yield service is inconsistent with the administrative boundary). 5) Huaneng Tibet Yarlung Zangbo River Hydropower Development and Investment Co., Ltd. gets the greatest value(USD 1.8million $) from the use of water yield service, while China Energy Tibet Electric Power Co., Ltd. gets the smallest(USD 389.1 thousand $). 6) Counties near the lower reaches have gained more economic benefits, while the water yield service they provide have the lowest contribution to hydropower production. Our approach linked water yield ecosystem service and hydropower development effectively, and revealed their complex eco-economic relationship between producers and beneficiaries of ecosystem services, which provides key insights for the designing of a potential PES mechanism.