Measurement and assessment of water resources carrying capacity in Henan Province,China

* Corresponding author.



Measurement and assessment of water resources carrying capacity in Henan Province,China

Ming Dou*,Jun-xia Ma,Gui-qiu Li,Qi-ting Zuo

College of Water Conservancy and Environment,Zhengzhou University,Zhengzhou 450001,PR China

Received 29 September 2013; accepted 25 December 2014

Available online 7 May 2015

* Corresponding author.

Abstract

As demands on limited water resources intensify,concerns are being raised about water resources carrying capacity (WRCC),which is defined as the maximum sustainable socioeconomic scale that can be supported by available water resources and while maintaining defined environmental conditions.This paper proposes a distributed quantitative model for WRCC,based on the principles of optimization,and considering hydro-economic interaction,water supply,water quality,and socioeconomic development constraints.With the model,the WRCCs of 60 subregions in Henan Province were determined for different development periods.The results showed that the water resources carrying level of Henan Province was suitably loaded in 2010,but that the province would be mildly overloaded in 2030 with respect to the socioeconomic development planning goals.The restricting factors for WRCC included the available water resources,the increasing rate of GDP,the urbanization ratio,the irrigation water utilization coefficient,the industrial water recycling rate,and the wastewater reuse rate,of which the available water resources was the most crucial factor.Because these factors varied temporally and spatially,the trends in predicted WRCC were inconsistent across different subregions and periods.©2015 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords:Water resources carrying capacity; Hydro-economic interaction; Sustainable socioeconomic scale; Water resources carrying level; Henan Province

E-mail address: dou_ming@163.com (Ming Dou).

Peer review under responsibility of Hohai University.

http://dx.doi.org/10.1016/j.wse.2015.04.007

1674-2370/©2015 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.Introduction

The concept of carrying capacity is rooted in demography,biology,and applied ecology (Clarke,2002).In ecology,carrying capacity is defined as the maximum population of a species that a habitat can support without permanent impairment of the habitat's productivity (Rees,1997).Water resources carrying capacity (WRCC)is a new concept that has not yet been clearly defined and described.Some researchers consider WRCC to be the capacity of water resources to sustain a society at a defined good standard of living,while others consider it the threshold level of water resources at which an environment is capable of supporting the activities of human beings (Seidl and Tisdell,1999; Li et al.,2000).Internationally,not many breakthroughs have been achieved in the WRCC research; the topic has only been considered briefly in theories of sustainable development (Ofoezie,2002).Some scholars have used terms such as sustainable water utilization,the ecological limits of water resources,or the natural system limits of water resources to express the meaning of WRCC (Hunter,1998; Falkenmark and Lundqvist,1998).Studies focusing exclusively on WRCC have primarily been conducted in China.The concept of WRCC was first applied to the Urumqi River Basin in China in 1989 (Shi and Qu,1992; Feng et al.,2006).It has been a topic of significant debate since 2001,and represents a new academic frontier (Long et al.,2004).

One definition of WRCC,and the definition used in this study,is the maximum sustainable socioeconomic scale based on available water resources and maintenance of good,defined environmental conditions (Dou et al.,2010).In this concept,the socioeconomic scale is the overall size of a regional socioeconomic system in a certain period,and can be represented by a series of socioeconomic indices (such as total population,urbanization ratio,industrial structure,and grain yield).Good environmental conditions mean a suitable living environment for human beings and the ecological system,in particular good water quality and a healthy aquatic environment.WRCC is an indicator of regional sustainability,and achieving regional sustainability is important because social institutions and ecological functioning are closely linked at this scale (Graymore et al.,2009).Therefore,research on WRCC should be based on two premises: First,it must be possible to sustain the normal operation of a regional socioeconomic system,and as a result researchers must calculate the quantity of water resources required to sustain these social service functions.Second,it is necessary to evaluate the maximum socioeconomic scale that water resources can sustain after meeting the needs of the ecosystem.

Regional carrying capacity depends on water resources.There have been many theoretical studies of carrying capacity based on regional water resources because this concept is most often considered within a larger theoretical context of sustainable development.In particular,severe water shortage problems have forced the Chinese government to initiate a series of studies to determine the carrying capacity based on regional water resources in arid and semi-arid areas,such as western China and the North China Plain (Xia and Zhu,2002; Dou et al.,2010; Zai et al.,2011).In recent years,with increasingly serious water pollution,there have even been some studies conducted in eastern China,where water resources are abundant (Liu and Borthwick,2011; Liu,2012).Furthermore,Falkenmark and Lundqvist (1998)have used estimates of the maximum global use of water resources to study how carrying capacity is determined by regional water resources.The National Research Council (NRC)(2002)studied the Florida Keys Basin's carrying capacity in the United States under different land-use scenarios.Lane et al.(2014)offered a Carrying Capacity Dashboard (QUT,2012)to highlight one way in which some basic resource-based parameters have been utilized.In practice,carrying capacity is often estimated by comparing stress on the environment (e.g.,demand of natural resources)against environmental thresholds (e.g.,available natural resources)(Clarke,2002; Oh et al.,2005).

On the whole,the current studies on WRCC emphasize harmonization of the demands of socioeconomic development with the supply of water resources.Regional socioeconomic systems and water resources systems are often represented using areas such as river basins,which allow researchers to analyze the systems' structures,functions,and processes and determine the WRCC.In China,the regional socioeconomic scale may be determined by the urban population growth rate and economic development goals.Constraints imposed by the availability of water and other natural resources are rarely considered in planning,which may explain why most Chinese cities are facing severe water shortages and experiencing environmental problems (Zhang et al.,2010).Therefore,it is necessary to develop a suitable methodology to effectively describe hydro-economic interaction in highly populated regions and to choose the best strategies to alleviate the conflict between socioeconomic development and water resources exploitation.

Henan Province,China's most populous province and the province with the fifth highest gross domestic product (GDP),has long suffered from an intense conflict between the limited water resources and the rapid growth of water demand.In this study,we developed a method for calculating Henan's WRCC based on available water resources and relevant water environment protection goals,and analyzed spatial and temporal variations of the WRCC.First,considering the spatial differences of the economic development level and water resources conditions,a distributed hydro-economic model was developed to describe the interaction between the socioeconomic and water resources systems.Second,a WRCC quantification model was developed to identify the maximum sustainable socioeconomic scale based on the hydroeconomic interaction relationship and a series of constraint conditions.Finally,on the basis of the models,Henan Province's WRCC was calculated for different development periods,and the change tendency of the water resources carrying level was analyzed.

2.Framework and methodology

2.1.Overview

Research on WRCC involves many disciplines,including hydrology,ecology,environmental sciences,economics,sociology,and management science (Zhang et al.,2010).Many methods can be used,of which the most common are trend analysis (Liu,2012),the fuzzy comprehensive evaluation method (Prato,2009),system dynamics (Feng et al.,2008; Dang and Guo,2012),multi-objective decision-making and analysis (Xu and Cheng,2000),the large-scale system theory,the optimization method,and the projection pursuit approach (Zhang and Guo,2006; Liu and Borthwick,2011).Trend analysis is based on empirical analysis of some socioeconomic indices under water resources constraints.The fuzzy comprehensive evaluation method is a common assessment method based on a set of index systems.System dynamics can reflect the interaction and feedback mechanism between human activities and the water resources system.Multiobjective decision-making and analysis can obtain the maximum sustainable socioeconomic scale under a series of water environmental and resources constraints.The large-scale system theory can use the idea of decomposition and coordination to solve a large-scale system problem.The optimization method finds the global optimal solution for complex problems based on given criteria.Finally,the projection pursuit approach is a newstatistical method solving multidimensional socioeconomic and water resources system problems.From a management perspective,the large-scale system theory and the optimization method are most appropriate because the former shows the interaction between thesocioeconomic and water resources systems,and the latter is convenient for management and decision-making.In this study,we developed a quantitative method for determining WRCC based on these two theories,and synchronously modified it to transform it into a distributed model that considers spatial differences of the economic development level and water resources conditions of the study area.The research framework was as follows:

(1)The study area was divided into 60 subregions based on the intersections of 18 administrative divisions of Henan Province and 21 third-level sub-catchments of the four firstlevel river basins.The division of sub-catchments was undertaken according to The Technical Outline of National Comprehensive Planning of Water Resources (GIWRHPD,2006).The reason we divided the study area in this way is that spatial differences among available water resources are determined by the third-level sub-catchments in which rainfall and runoff conditions are different,whereas those of water demand are determined by the administrative divisions and associated with economic development levels.The subregions were then connected by a hydraulic relationship based on the river systems of the study area (Fig.1),demonstrating the transfer processes of water and contaminants between the subregions.

(2)A distributed hydro-economic model,used to represent the interaction between socioeconomic development and water resources exploitation,was developed based on the large-scale system theory.

(3)Based on the hydro-economic model,an optimal model for calculating WRCC was developed.The model seeks to sustain the maximum socioeconomic scale as the optimization objective,maintain ideal water quality of water function areas,and meet basic water supply and livelihood guarantees as the constraint conditions.

(4)An assessment method with a standard water resources carrying level,which reflected the development potential of the subregions in the future,was developed.

(5)The WRCC of 60 subregions in Henan Province was calculated for different development periods,and the main factors restricting socioeconomic development of Henan Province were identified by these models.

2.2.Development of hydro-economic model

A hydro-economic model was developed to describe the interaction between the socioeconomic and water resources systems in Henan Province.This model consists of three calculation modules: the socioeconomic system module,water quantity module,and water quality module.

2.2.1.Socioeconomic system module

This module was developed to simulate the pressure of socioeconomic development on the water resources system inside each subregion,such as socioeconomic development in the future,natural resources consumption,and environmental pollution.This module consists of three components:

Fig.1.Sketch of water resources calculation nodes.

(1)Forecast of socioeconomic development level: This was used to forecast the future socioeconomic scale according to the planning development goals of Henan Province.To describe the hydro-economic interaction,it is essential to select several representative socioeconomic indices to reflect the intensity of human activity and its influence on the environment.In this study,the following indices were selected: (a)indices A: population indices,such as total population,the urbanization ratio,the growth rate of the population,and the floating population; (b)indices B: economic indices,such as GDP,the proportion of the economy made up by the three industries,the increasing rate of GDP,livestock number,and grain yield; (c)indices C: indices that were used to reflect the levels of resource consumption and pollution discharge,such as interbasin water transfer,water use quota,water consumption rate,and the pollutant discharge coefficient of various industries; and (d)indices D: indices that were used to reflect the development level of technology,such as the wastewater treatment efficiency,the wastewater reuse rate,the industrial water recycling rate,and the irrigation water utilization coefficient.In this study,we selected 2010 as the baseline year and 2011 e 2030 as the planning years.Indices A and B were used to forecast the socioeconomic scale of the study area in the planning years,and indices C and D were used to simulate the conditions of water resources supply and use as well as pollutant discharge.In the forecast of the socioeconomic scale,the indices of socioeconomic development level (e.g.,the urbanization ratio,the growth rate of the population,and the proportion of the economy made up by the three industries)of the study area were first analyzed and forecasted on the basis of the statistical data from 1980 to 2000.Then,the values of the socioeconomic scale indices (e.g.,total population,GDP,livestock number,and grain yield)were calculated according to the functional relationship between them and the parameters above.Finally,the forecasted results were verified and adjusted according to the target values.

(2)Calculation of water use (or demand)and consumption: In the baseline year,the productive (including industrial,agricultural,and service industrial),domestic (including urban domestic and rural domestic),ecological,and total water uses were obtained from the statistical data of water conservancy departments; in the planning years,the productive,domestic,ecological,and total water demands were forecasted with the water quota method,which constructs a functional relationship between the socioeconomic or ecological indices and water demand quota.The corresponding water consumption was then calculated by multiplying the water use (or demand)by the water consumption rate.

(3)Calculation of pollutant discharge: The pollutant discharges arising from point sources (including industrial and urban domestic pollutant discharges)and non-point sources were calculated with the pollutant-discharging coefficient method,which constructs a functional relationship between the socioeconomic indices and pollutant-discharging coefficients.The determination of the pollutant-discharging coefficients was based on comprehensive consideration on the industrial source,domestic lifestyle,and pollution source treatment level.The river pollution load was then calculated by multiplying pollutant discharge quantities into rivers by the river load coefficients derived empirically on the basis of the degradable characteristic of pollutants,distance from the pollution source to rivers,and canalization level of drainage channels.

2.2.2.Water quantity module

First,the hydraulic connection among the subregions was established,and a sketch of the water resources calculation node was made (Fig.1).All of the variables pertaining to water resources in a subregion,such as the volume of inflow and outflow,self-produced and transferred water,and water consumption,were determined during a certain period of time.According to the relationships between the unknown variables and the given variables,the unknown variables were expressed by the approximate functions of the given variables and then input into the model.The unknown parameters were identified and inserted into the model.According to the calculated multiple correlation coefficients,the regression results were evaluated,and the identified parameters were input into the model.The values of all the water volumes were calculated and checked to determine whether the calculations conformed to the law of mass conservation.In this study,the precipitation and inflow data of 33 hydrological stations in Henan Province were used in the calculation of water quantity.For any time period Dt,there is a water balance equation as follows: where P is the volume of precipitation,in m3; QTis the volume of transferred water,in m3; Qinis the volume of water inflow,in m3; E is the volume of evapotranspiration (including water surface and land surface evaporations),in m3; Ei,Ea,Eud,and Erdare the volumes of industrial,agricultural,urban domestic,and rural domestic water consumptions,in m3; Qoutis the volume of water outflow,in m3; and DV is the volume change in water storage,in m3.

2.2.3.Water quality module

Along with the water quantity module,a module for water quality was also developed based on the law of mass conservation.Because organic pollution was the most outstanding problem of surface water pollution in Henan Province,the permanganate index (CODMn)was selected as the only water quality index in the following calculation process.In this study,the CODMnconcentrations at 21 monitoring sections in Henan Province were used in the calculation of water quality.For any time period Dt,the following pollutant balance equation was satisfied: where Qsiand Qsoare inflow and outflow volumes of surface water,respectively,in m3; Cinand Coutare CODMnconcentrations of inflow and outflow,respectively,in mg/m3; DC is the change in CODMnconcentrations over the time period Dt,in mg/m3; Spsand Snsare river pollutant loads from point sources and non-point sources,respectively,in mg; Vsis the volume of surface water storage,in m3; Wuis the volume of total water use,in m3; and b is the comprehensive reduction rate of CODMn,which is related with river length,flow velocity,and pollutant characteristics,and determined by a onedimensional steady-state pollutant migration and transformation equation,which is dimensionless (Dou et al.,2010): where x1is the river length from the inflow section to the outflow section of a subregion,in m; x2is the river length from the sewage outfall section to the outflow section,in m; u is the average flow velocity,in m/s; and k is the degradation coefficient of CODMn,in d1.

2.2.4.Coupling of modules

The modules of the water quantity,water quality,and socioeconomic system are correlated and interdependent,and they must be coupled to simulate and forecast the interaction between the socioeconomic and water resources systems.The coupling relationship of the modules is illustrated in Fig.2.In the analysis of the entire study area,based on the inputeoutput relationship of each subregion shown in Fig.1,all subregions were combined.

2.3.Development of WRCC quantification model

The objective of the WRCC quantification model is to find the maximum socioeconomic scale of Henan Province.The socioeconomic scale is usually represented by a series of indices,i.e.,urban population,rural population,GDP,industrial added value,agricultural added value,and grain yield.If these indices are included in the objective function,solution of the model will become one solution of the multi-objective optimization problems.For the sake of a convenient solution,all of these indices change proportionally with one another during the search for optimal values.Therefore,the objective function is simplified as a single-objective function based on a change ratio a and can be expressed as follows: where QWRCCis the value of WRCC; a is the change ratio,which is a percentage used to minimize or magnify the socioeconomic scale when solving the WRCC quantifying model; Ppopis the population; and RGDPis the value of GDP,in RMB.The constraints of the WRCC quantifying model are as follows.

(1)Simulation of hydro-economic interaction: The hydroeconomic model described above is embedded in the WRCC quantifying model as an important constraint.It plays an important part in constructing the relationship between the objective function and other constraints,realizing the transmission and feedback of data between the socioeconomic and water resources systems.

(2)Water supply constraint: Total water use of each subregion must be less than or equal to its available water supply.where Wp,We,and Wdare,respectively,the volumes of productive,ecological,and domestic water use,in m3,and Wasis the volume of available water supply,including available surface water,available groundwater,transferred water from outside subregions,and wastewater reuse,in m3.

Fig.2.Coupling of modules.

(3)Water quality concentration constraint: The calculated value of CODMnconcentration in representative water function areas in each subregion must be less than or equal to the corresponding control objective value:where C is the calculated value of CODMnconcentration,and CSis the control objective value of CODMnconcentration,in mg/L.In this study,there were 60 water function areas selected as the representative concentration control nodes,according to the following principles: (a)these water function areas were the major stream segments in the subregions; (b)these water function areas received the greatest mass of flow and pollutant afflux in the subregions where they were located; and (c)for subregions in which hydraulic connections were very complex,the number of representative water function areas was increased appropriately.

(4)Socioeconomic development level constraint: Per capita GDP and per capita share of grain in each subregion must be greater than or equal to a certain living standard: where Raand RSare the calculated values and the minimum living standards of per capita GDP,respectively,in RMB; and Faand FSare the calculated values and the minimum living standards of per capita share of grain,respectively,in tons.The minimum living standards were obtained from The Future Development Outline of Henan Province (PGHP,2010).

The WRCC quantifying model is composed of the objective function and constraints.Applying the numerical iteration method (NIM),an approximate optimal solution that meets all of the constraints is obtained.When searching for the optimum value with the NIM,the actual (or forecasted)socioeconomic data input as the initial value is enlarged or reduced by adjusting a in a certain proportion and judging whether the result can satisfy the constraints.The search process is repeated until the difference in the a value of two adjacent searches is less than a certain error coefficient (the value is 0.01 in this study).At this time,the adjusted socioeconomic scale is the WRCC.

When solving the WRCC quantifying model,there arises a situation in which the QWRCCof a downstream subregion is zero or very small due to the severe pollution of inflow from upstream.The reason is that,because all the subregions in the study area are closely linked through hydraulic relationships,water use and pollutant discharge of a subregion will have a certain impact on downstream subregions,especially those in urban districts.Hence,for downstream subregions,this further diminishes the socioeconomic scale of adjacent upstream subregions,in addition to allowing them to adjust their own scale.Finally,a balance point,which takes into account the coordinated development between the upstream and downstream subregions,may be obtained.

2.4.Assessment of water resources carrying level

The water resources carrying level is used to express the degree of socioeconomic development pressure on water resources systems (Dou et al.,2010).The water resources carrying level is the ratio of the actual (or forecasted)socioeconomic scale in the baseline (or planning)year to the WRCC.When the water resources carrying level is greater than 1.0,the actual (or forecasted)socioeconomic scale has exceeded the WRCC,and the overload becomes more severe as it increases; when it is equal to 1.0,the socioeconomic scale is at the threshold value of WRCC; and when it is less than 1.0,the socioeconomic scale is within the WRCC range,and the development potential becomes greater as it decreases.Furthermore,the water resources carrying level is divided into five categories: when it is less than or equal to 0.6,it falls into the fully loaded category; between 0.6 and 1.0,it falls into the suitably loaded category; between 1.0 and 1.5,it falls into the mildly overloaded category; between 1.5 and 2.0,it falls into the moderately overloaded category; and when it is greater than or equal to 2.0,it falls into the severely overloaded category.

3.Results and discussion

3.1.Calibration and validation

In the simulation of the hydro-economic interaction process,the twenty sensitive parameters listed in Table 1 were selected for Henan Province's hydro-economic model,including seven socioeconomic parameters,seven water quantity parameters,and six water quality parameters.

In order to demonstrate the simulation effect of the hydroeconomic model,three indices,average relative error,the correlation coefficient,and the efficiency coefficient (Zhang et al.,2013),were used to measure the simulation precision.Both discharge and CODMnconcentration were simulated using this model,and the applicability of the model was evaluated by investigating the processes of change in the variables.The simulation results are summarized in Table 1.In the water quantity simulation,there were 21 stations whose absolute value of average relative error values were less than 15%,accounting for 64% of all the stations.The average correlation coefficient was 0.72,and the average coefficient of efficiency was 0.45.In the water quality simulation,there were 13 sections,whose absolute value of average relative error values were less than 45%,accounting for 62% of all the sections,and 15 sections whose correlation coefficients were greater than 0.40,accounting for 71% of all the sections.According to the results of the simulation,we concluded that the model was a satisfactory and reasonably representative of the hydro-economic interaction.

3.2.WRCC in baseline year

We selected 2010 as the baseline year,when the WRCC of 60 subregions in Henan Province under actual conditions was determined using the WRCC quantification model.The calculation conditions applied in the WRCC quantification model in the baseline year were as follows: (a)hydrological conditions were adopted based on statistical precipitation,evaporation,and runoff data from 2010; (b)socioeconomic conditions were adopted based on statistical socioeconomicindices,such as population,GDP,livestock number,and grain yield,from 2010; (c)water resources conditions were adopted based on statistical data on water resources exploitation and utilization from 2010; and (d)water environmental conditions were adopted based on monitored water quality concentrations of the rivers and statistical pollutant discharge and pollutant load amounts of rivers from 2010.

Table 1　Calibrated parameters of hydro-economic model in Henan Province.

Based on these calculation conditions,the WRCC of each subregion was calculated using the model,and the water resources carrying level was determined.Then,the WRCC of 18 cities and of the entire province were aggregated according to the calculation results.The results are shown in Table 2,and the spatial distribution of the water resources carrying level is shown in Fig.3.

The results in Table 2 indicate that the water resources carrying level of Henan Province was 0.98 in 2010,which falls into the suitably loaded category.The loaded total population wasand the loaded GDP value wasRMB.These were 102.5% of the actual values of the province (the actual total population was4and the actual GDP value was108RMB in 2010).There were 33 overloaded subregions,accounting for 55% of the total subregions.Of these 33 overloaded subregions,nine subregions fell into the severely overloaded category,seven subregions fell into the moderately overloaded category,and 17 subregions fell into the mildly overloaded category.Despite the fact that 2010 was a wet year and water resources in that year were correspondingly abundant,the actual socioeconomic scale of some subregions was nonetheless found to exceed their WRCC.

The subregions with higher water resources carrying levels included some subregions in the headwaters of the Huaihe River and its major branches,such as subregion 13 (Luoyang City),subregion 32 (Nanyang City),subregion 35 (Nanyang City),subregion 49 (Xinyang City),and subregion 51 (Xinyang City).These subregions lie in the southern part of Henan Province,where there is abundant precipitation as well as low water consumption and pollutant discharge,and the high water resources carrying level of these subregions was due to their slower production.The others were the subregions along the main stream of the Yellow River,such as subregion 2 (Zhengzhou City),subregion 7 (Kaifeng City),subregion 9 (Luoyang City),subregion 19 (Xinxiang City),and subregion 60 (Puyang City).These subregions have abundant water flowing through them even though they generate less water because of scarce precipitation and small catchment areas.In the meantime,water consumption and pollutant discharge in these subregions are low due to their small socioeconomic scale.

The subregions with lower water resources carrying levels included some subregions in the Haihe River Basin,such as subregion 4 (Zhengzhou City),subregion 20 (Jiaozuo City),subregion 30 (Jiyuan City),subregion 43 (Anyang City),subregion 44 (Anyang City),subregion 45 (Anyang City),subregion 57 (Puyang City),and subregion 59 (Puyang City).The Haihe River Basin is one of the areas that suffers from severe water shortage,in which precipitation and generated water amount are both low.At the same time,these subregions are relatively isolated,and replenishment of water and transferred water both remain at low levels.The others are the subregions in the central urban areas of Henan Province,such as subregion 1 (Zhengzhou City),subregion 6 (Kaifeng City),subregion 17 (Xinxiang City),subregion 24 (Xuchang City),subregion 53 (Zhoukou City),subregion 54 (Zhumadian City),subregion 46 (Shangqiu City),and subregion 47 (Shangqiu City).Although these subregions have certain available waterresources,their water consumption and pollutant discharge are large because of their large socioeconomic scale and unreasonable industrial structure.For example,the dominant industries are energy,machinery,and raw material industries in subregion 1 (Zhengzhou City); modern industry in subregion 17 (Xinxiang City); and machinery manufacturing and fur processing industries in subregion 24 (Xuchang City).

Table 2　WRCC in baseline year under actual conditions.

3.3.WRCC in planning years

Fig.3.Assessment of water resources carrying level in baseline year.

The planning years were from 2011 to 2030,and 2030 was selected as a key time node to be introduced and compared with the baseline year in this study.The calculation conditions in the planning years were as follows: (a)hydrological conditions based on statistical data on precipitation,evaporation,and runoff at the hydrological frequency of 50%; (b)socioeconomic conditions based on forecasted socioeconomic index values from 2011 to 2030,according to future development goals from the Central Plains Economic Zone Development Planning (PGHP,2012); (c)water resources conditions based on the planning water resources utilization level from 2011 to 2030 according to the Henan Province Water Resources Integrated Planning (HWPECC,2008); and (d)water environmental conditions based on the controlled water qualityconcentration in rivers and forecasts of pollutant discharge and load amounts of rivers from 2011 to 2030,according to environmental protection goals from the Henan Province Environmental Protection Planning (HPEPB,2012).

Based on the calculation conditions described above,the WRCC of each subregion was calculated and the water resources carrying level was determined.The aggregated results for the entire province from 2011 to 2030 are shown in Table 3,and spatial distribution of the water resources carrying level in 2030 is shown in Fig.4.

The results in Table 3 indicate that the water resources carrying level of Henan Province will be 1.31 in 2030,which falls into the mildly overloaded category.The loaded total population of the province in 2030 will be 8 589.1 104,which is a decrease of4from 2010 with a decrease rate of 16.33%.The loaded urban population was predicted to increase byover that in 2010,with an increase rate of 41.84%.The loaded rural population was predicted to decrease by 3 271.3 104from that in 2010,with a decrease rate of 50.70%.This is due to the rapid urbanization ratio predicted to occur from 2010 to 2030,which will result in significant migration from the countryside to the city.The loaded GDP value of the province was predicted to be8RMB in 2030,which is an increase ofRMB over that in 2010,with an increase rate of 75.65% from 2010 to 2030.The proportions of agricultural,industrial,and service industrial added values were predicted to change dramatically,from 13.9: 51.5: 34.6,in 2010 to 4.5: 42.4: 53.1,in 2030.In the future,the service industry will be the dominant industry rather than traditional industry.

There are 38 subregions predicted to be overloaded,accounting for 63% of total number of subregions.Of these 38 subregions,12 subregions were predicted to be severely overloaded,nine subregions were moderately overloaded,and 17 subregions were mildly overloaded.For 29 subregions,the water resources carrying level was predicted to decrease from 2010 to 2030.However,there were also 16 subregions in which the water resources carrying level was predicted to improve from 2010 to 2030.For example,subregion 20 (Jiaozuo City),subregion 29 (Jiyuan City),subregion 30 (Jiyuan City),subregion 38 (Hebi City),and subregion 39 (Sanmenxia City)will move into the suitably loaded category.

The water resources condition (i.e.,available water resources)is a crucial factor restricting socioeconomic development of water-deficient areas,such as the northern and central areas of Henan Province.According to the calculation results,both the water resources amount and the WRCC value in 2010 are greater than those predicted in 2030.The main reason is that the hydrological conditions for 2010 are based on actual data,and 2010 was a wet year,while the hydrological conditions for 2030 are based on designed data,and 2030 is predicted to be a normal year.In addition,the influences of future socioeconomic development and technological progress on the WRCC are significant in the following ways: (a)The increase of the urbanization ratio and GDP will lead to the growth of water demand quota and total water demand (Fig.5(a)and (c)),which will contribute to a decrease in the WRCC.(b)The irrigation water utilization coefficient,industrial water recycling rate,and wastewater reuse rate will improve with the progress of science and technology (Fig.5(d)),which will contribute to an increase in the WRCC.(c)Total water supply and interbasin water transfer will increase due to the construction of various water transfer projects (Fig.5(b)),which will contribute to an increase in the WRCC.Because the indices of the increasing rate of GDP,urbanization ratio,irrigation water utilization coefficient,industrial water recycling rate,wastewater reuse rate,and interbasin water transfer will vary temporally and spatially,and the trends in the WRCC vary among the subregions and over time.From the temporal perspective,the number of overloaded subregions exhibits an increasing trend over the period from 2011 to 2016,and a decreasing trend over the period from 2017 to 2030 (Fig.6(a)),and the loaded population exhibits an opposite trend,decreasing at first and then increasing (Fig.6(b)).In the former period,the negative factors (e.g.,the increasing rate of GDP and urbanization ratio)are more influential than the positive factors (e.g.,the irrigation water utilization coefficient,industrial water recycling rate,wastewater reuse rate,and interbasin water transfer)when the water resources conditions are consistent,but in the later period,the positive factors are more influential on the WRCC than the negative factors.A significant reason is that the middle route of the South-to-North Water Transfer Project of China will be completed and begin transferring water in 2017.With the construction of this project,Henan Province could increase additional freshwater byeach year,accounting for 14.2% of the province's available water supply in 2017.Basically,the water demand of 11 large and medium-sized cities in Henan Province along the middle route will be met,but the water demand of other cities will remain the same.Meanwhile,the loaded GDP value exhibits a consistently increasing trend over the period from 2011 to 2030 (Fig.6(c)).On the whole,the indices of socioeconomic development and urbanization show increasing trends,but those of the rural population and the proportion of agricultural added value show decreasing trends (Fig.6(d)).

Table 3　Henan Province's WRCC in planning years under forecasted conditions.

Fig.4.Assessment of water resources carrying level in 2030.

Fig.5.Trends of socioeconomic development and water resources indices in planning years.

4.Conclusions

In this paper,the concept of WRCC was discussed,and some calculation and evaluation methods for WRCC were presented.Using these methods,the WRCC of Henan Province was determined for the baseline and planning years,and the following conclusions are drawn:

(1)A distributed quantitative model for WRCC based on the large-scale system theory and optimization method was developed,and Henan Province's WRCC was calculated for different development periods.

(2)According to the simulation results of the model,there were 33 overloaded subregions in 2010; the loaded total population wasand loaded GDP value wasRMB.The province's water resources carrying level is suitably loaded.

(3)Based on the planning development goals,the WRCC from 2011 to 2030 was calculated.According to the simulation results,there will be 38 subregions overloaded in 2030,the loaded total population will beand the loaded GDP value will be8RMB.The province's water resources carrying level will be mildly overloaded.

Fig.6.Trends of socioeconomic indices and number of overloaded subregions in planning years.

(4)WRCC is influenced by many factors,of which available water resources is the most crucial.The main factorsaffecting the WRCC are different from 2011 to 2030.In the period from 2011 to 2016,the negative factors (e.g.,the increasing rate of GDP and urbanization ratio)that contribute to a decrease of the WRCC are more influential than the positive factors (e.g.,the irrigation water utilization coefficient,industrial water recycling rate,wastewater reuse rate,and interbasin water transfer)that contribute to an increase of the WRCC when the water resources conditions are consistent,and the converse is true for the latter period from 2017 to 2030.

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