Economic Value Produced By River Ecological Base Flow And Its Temporal-spatial Variations In Water Shortage Area

For perennial rivers,river ecological base flow keeps water in river channel all year round,maintains continuity and integrity of river and holds health for river ecosystem.It is a hotspot of water resources management.In water shortage area,dry season is critical for river ecological base flow protection,and in this period the contradiction between river ecological base flow and local production water use is serious.Human gradually realizes the importance of river ecological base flow,but it is often at a disadvantage in river water resources distribution,and hard to protect.The reason for this is that the economic value produced by river ecological base flow is difficult to quantify.Therefore,scientific and accurate establishment of quantitative calculation method of economic value produced by river ecological base flow,and research of economic value produced by river ecological base flow and its temporal-spatial variations are an important basis for coordinating the contradiction between supply and demand of river water resources and optimizing the allocation of water resources by means of economics.It also provids theoretical support for long-term protection mechanism of river ecological base flow.Economic value produced by river ecological base flow is the role of river ecological base flow in avoiding river shrink or dry up,and maintaining ecosystem health and natural process of river.Firstly,we took river ecological base flow in water shortage area as research object,and identified its functions and value composition based on the theory and method of resource and environment economics.Secondly,we established calculation method of economic value produced by river ecological base flow,calculation method of temporal-spatial variation of economic value produced by river ecological base flow on reach scale,and calculation method of temporal-spatial variation of economic value produced by river ecological base flow on watershed scale,respectively.Thirdly,we studied temporal-spatial variation characteristics and its driving forces of economic value produced by river ecological base flow from reach scale and watershed scale,respectively.Finally,we took the Wei River as an example to apply and verify these theoretical methods.The main conclusions were as follows:(1)Functions and value composition of river ecological base flow.Economic value produced by river ecological base flow was composed of natural value,eco-environmental value and social value by referring to functions classification of river.Natural value divided into avoiding dried up value,hydrologic cycle value,geology value and sediment transport value.Eco-environmental value divided into sustaining floodplain wetland ecosystems value,nutrient transport value,water purification value and increasing soil organic content value.Social value divided into fishery production value,recreation value and improving quality of life value.A certain amount of river ecological base flow can support multiple sub-values simultaneously.(2)Calculation method of economic value produced by river ecological base flow.We established quantitative calculation method for each sub-value using the assessment techniques of resource and environment economics.On the basis of calculation results of sub-values and the relationship between sub-values,we determined the maximum economic value supported by each kind of water requirements of river ecological base flow respectively,and we can obtain its total economic value by summing up the independent parts.This method can remove repeated calculation and realize quantitative calculation of economic value produced by river ecological base flow as accurately as possible.(3)Calculation method of temporal-spatial variation of economic value produced by river ecological base flow on reach scale.We proposed temporal-spatial variation coefficient of economic value produced by river ecological base flow.It can represent influence of factors,such as precipitation,river flow,water quality,human water consumption and capability to pay,on economic value produced by river ecological base flow.On this basis,combined calculation method of economic value produced by river ecological base flow,we established calculation method of temporal-spatial variation of economic value produced by river ecological base flow on reach scale.We used total economic value and unit economic value to represent temporal-spatial variation of economic value produced by river ecological base flow on reach scale.(4)Calculation method of temporal-spatial variation of economic value produced by river ecological base flow on watershed scale.According to the opportunity cost theory,we can assess economic value produced by river ecological base flow in water shortage area based on the maximum loss caused by other uses of river water resources due to water scarcity.Therefore,we evaluated water scarcity assessment on watershed scale by introducing assessment method of water scarcity that incorporates ecological base flow.Then,we established calculation method of temporal-spatial variation of economic value produced by river ecological base flow on watershed scale by combining assessment results of water scarcity and the opportunity cost method.We used unit economic value to represent temporal-spatial variation of economic value produced by river ecological base flow on watershed scale.(5)Case study.We took the Wei River as an example to apply and verify these theoretical methods.The Guanzhong Section of the Wei River was the study range of reach scale,and the Wei River Basin was the study range of watershed scale.(a)The minimum total economic value produced by river ecological base flow in the Guanzhong Section of the Wei River was 4.5 billion yuan in 2017.(b)From 1980 to 2017,annual variation range of total economic value produced by river ecological base flow in each section of the Wei River in non-flood season was 0.30—0.42 billion yuan,and annual variation range of unit economic value produced by river ecological base flow was 0.86—6.40 yuan per cubic meter.In the typical years,monthly variation range of total economic value produced by river ecological base flow in each section of the Wei River was 0.04—0.08 billion yuan,and monthly variation range of unit economic value produced by river ecological base flow was 0.94—14.34 yuan per cubic meter.There existed significant negative correlations between economic value produced by river ecological base flow and precipitation,river flow or comprehensive pollution index(water quality),and precipitation,river flow and water quality were main driving forces of economic value produced by river ecological base flow on reach scale.(c)We established prediction model of economic value produced by river ecological base flow of the Wei River,and simulation results were relatively satisfied(R2=0.95).(d)Variation range of unit economic value produced by river ecological base flow in the Wei River Basin was 0.15—3.09 yuan per cubic meter using scenario analysis.The areas with higher economic value produced by river ecological base flow of the Wei River Basin were mainly distributed in the Loess Plateau and the Guanzhong Plain.There existed significant spatial difference characteristics between economic value produced by river ecological base flow and climate represented by precipitation,and significant spatial agglomeration characteristics between economic value produced by river ecological base flow and land use intensity.Climate and land use were main driving forces of economic value produced by river ecological base flow on watershed scale.(e)Compared with similar research,the calculation results were relatively reasonable.It indicated that the theoretical methods proposed in this paper were relatively scientific and reliable to some extent.These methods can better provide theoretical support for quantitative research of economic value produced by river ecological base flow and scientific management of limited water resources coming from river.