2016 International Conference on Mathematical, Computational and Statistical Sciences and Engineering (MCSSE 2016) ISBN: 978-1-60595-396-0
Water Resource Demand Analysis in the Loess Plateau Area Based on
Food Security: A Case Study of Changwu County in Shaanxi Province
You-yang YOU
International Business School, Yunnan University of Finance and Economics, Kunming, 650221, Yunnan China
Keywords: Water resources, Food security, Gray relational analysis, Water production function, Loess plateau, Changwu county.
Abstract. The shortage of water resources has been a major problem in the Loess Plateau. Under the situation of a steady increase in population, cultivated land gradation and rapid development of regional economy, how to achieve food security has been becoming an important issue in this region. Thus, a typical case study of Changwu County in Shaanxi Province was conducted. With the help of grey correlation analysis method, it concluded that the water resource is the leading factor in limiting the local food safety. Furthermore, the water consumption and water demand at various sectors are compared and analyzed. Then, the crop-water production function was introduced to optimize the irrigation water allocation. The paper finally discussed the development strategy on water resources utilization and food security, which would provide a scientific basis for the water resources exploitation and be a guarantee for the food security in Changwu County.
Introduction
Lester R. Brown, Head of the World Watch Institute, pointed out that “The sharp shrinkage of China's agricultural water supply constitutes an increasing threat to the world’s food security” in his paper entitled China's Water Shortage Could Shake World Food Security [1]. Loess Plateau is an important birthplace of the Chinese agricultural civilization and the world's major agricultural area, with the most concentrated population, resource and environmental contradictions, the highest difficulty in governance and the largest number of impoverished population. As the cultivated land occupies 12.2% nationwide, whereas the water resources occupy merely 2.2%, how to achieve the food security in the area is correlated with the security issue of the whole country and even the world. In response, many scholars have conducted in-depth and intensive studies on the production efficiency of water resource [2] and the restrictions on natural, social and economic factors and other comprehensive factors on the food production [3] in terms of ecological rationality of water resources [4], threshold of crop water demand and optimal allocation of irrigation water quota. However, previous studies are comprehensive ones for optimal allocation with a lack of analysis and determination of factors restricting grain production. In this case study, Changwu County, Shaanxi Province, is taken for example.
Overview of Study Area
Changwu County, which is located in the hilly-gully area of Loess Plateau in the northwest of Shaanxi Province, is a national pilot cultivated land preservation and modern sustainable and
efficient agriculture county, with a total cultivated area of 11520 hm2, irrigated area of 5070 hm2
Study Method
Grey Correlation Analysis
Grey Correlation Analysis a method for analyzing the correlation degree among factors in the
system. It has been widely applied in practice[5]. The calculation formulas are shown in formulas
(1) and (2).
εi(k)=minimink|X0(k)-Xi(k)|+ρmaximaxk|X0(k)-Xi(k)|
|X0(k)-Xi(k)|+ρmaximaxk|X0(k)-Xi(k)| . (1)
γi=1 n∑ εi
N
k=1 (k) (i =1,2,…,m) .
(2)
In the formulas, εi(k) is the correlation coefficient; (k) and Xi(k)respectively represent
reference sequence and comparative sequence, namely the time sequence and the grain production
and the time sequence of its corresponding impacting factor; γi is the correlation degree; ρ is the
resolution coefficient, and valuated between 0 and 1, usually 0.5; n is the time sequence length.
Quota Method
The quota method defines the water demand of the object by multiplying the area of the regional study object with the water demand quota[6].
W = ∑Airi. (3)
In formulas (3), W is the total water demand (m3), Ai is the area of the study object i (m2); ri is the
water demand quota of the study object I (m3/m2).
Crop Water Demand Method
The calculation formula is shown as follows:
ET = EP + EI = ·P + δ·I. (4) In the formula, ET—evapotranspiration, EP—effective precipitation, refers to the part of precipitation that is reserved in leaves or infiltrated in soil to reduce the equal amounts of soil and water lost, and is obtained by multiplying the homochronous precipitation (P) with converted
coefficient (); the value is usually correlated with precipitation characteristics (such as rain
intensity and duration) and crop growth. EI—effective irrigation amount; I—actual irrigation amount; δ—irrigation water utilization coefficient.[7].
Optimal Allocation of Irrigation Water
The specific calculation procedures and methods are as follows[8]:
(1) Determination of optimized irrigated area at the maximum total production
Based on a given higher or appropriate nutrient supply and optimized irrigation system, the maximum production corresponding to each irrigation quota M (including when M = 0) is used to build the ideal or mostly ideal water production function Y=Y (M). The specific formula is shown as follows:
Y = 6273 + 13.8M - 0.0263M2 . (5)
Its general manifestation is a quadratic parabola, namely Y = a + bM + cM2. In the formula, Y is
the ideal or mostly ideal production per unit cultivated area after the optimization of irrigation quota in the study area; M i the study area irrigation quota (mm) of the study area. In formula (5), when M=0, Y refers to the production per unit area without irrigation condition, namely the production
per unit area in non-irrigated land, Y2 = 6.273×10-3 t·hm2; when M≠0, Y refers to the grain
production per unit area in irrigated land (Y1). Therefore, the total grain production in the study area
In the formula, Ya is the total grain production in the study area (t); A is the actual irrigated area
(hm2); A0 is the total cultivated area of the irrigated area (hm2); Y1 and Y2 are productions per unit
area of the irrigated land and the non-irrigated land (t·hm-2).
Under optimized irrigation quota conditions, the optimized irrigated area at the maximum total
production of the whole irrigated area (A′) can be determined through formula (6). When Ya’s
derivative with respect to A = 0, the formula is shown as follows:
A′=dY/dA=0. (7) Through the calculation, the solution satisfying the above formula will be that A tends to infinity.
Therefore, when A' = A0, the whole irrigated area has the largest production.
(2) Determination of irrigation quota at the maximum total production When dY/ dM = 0 in formula (5), the solution is as follows:
Mf=-b/2c (8)
Based on formula (5), in (8), b is 13.8, and c is -0.0263. Mf is the irrigation quota at the
maximum production per unit area in the whole irrigated area under the condition of sufficient water resources and irrigation (mm). In the sub-humid area with limited water resources, the
irrigation quota at the maximum production per unit area in the whole irrigated area (M1) is
inevitably lower than Mf calculated in formula (8). According to the characteristic curve of the
water production function and the above analysis on the optimized irrigated area, the optimal irrigation strategy under the condition of limited water resources is determined to be the equal
irrigation implemented in the whole irrigated area. That is to say, Ml at the maximum total
production in the whole irrigated area (Ml) is calculated in formula (9).
Ml = ηW0/ A′. (9)
In the formula, Ml is the irrigation quota at the maximum total production in the whole irrigated
area; W0 is the farmland irrigation water amount (10,000 m3); η is the irrigation water utilization
coefficient; A′ is the optimized irrigated area (hm2).
(3) The maximum production for optimized irrigation quota
The maximum production for the optimized irrigation quota is based on the optimized irrigated
area (A′) and the irrigation quota (Ml). The formula (8) is substituted into the formula (5), and then
the result and formula (7) are jointly substituted into the formula (6) to obtain formula (10):
Y′= Y1×A′ + Y2 (A0 - A′) = Y1×A0. (10)
In the formula, Y′ is the maximum production for the optimized irrigation quota; because A′= A0,
the equal irrigation is implemented in the whole cultivated land.
Results and Analysis
Grey Correlation Analysis on Grain Production and Major Input Factors of Changwu County
Through the qualitative judgment factors impacting the grain production, dominating factors are
selected as follows: X1(k)—pure fertilizer application amount (t), X2(k)—agricultural plastic film
consumption (kg), X3(k)—agricultural diesel consumption (t), X4(k)—water-saving irrigated area
(hm2), X5(k)—irrigation water consumption (10,000 m3), X6(k)—pesticide consumption (kg),
X7(k)—cultivated area (hm2), X8(k)—irrigable area (hm2), X9(k)—annual precipitation (mm),
X10(k)—grain production (t). On the basis of Changwu County Statistical Yearbook for 2000-2008,
Table 1. The correlation level of between the factors and grain production in Changwu County.
X1 X2 X3 X4 X5 X6 X7 X8 X9
0.76 0.83 0.69 0.52 0.83 0.77 0.77 0.96 0.88
Theoretic Water Demands of Changwu County
Ecological Water Demand
Forest Land Water Demand. According to the data of the land use change survey for Changwu
County, the existing forestland covers 18,016.99 hm2, but grows in an unsatisfactory state, with
great differences in quality. The existing forestland occupies 68.93% of the total forestland area, which is followed by the young afforested land (17.11%). Shrub-land and open forestland cover
143.653 hm2 and 2315.427 hm2, respectively. Through formula 3, the total theoretic water demand
of forestland in Changwu County is 96.59463 million m3, including 69.10817 million m3 of
forestland, 680,370 m3 of shrub-land, 10,74821 million m3 of open forestland, and 1,605,788 m3 of
young afforested land.
Grassland Water Demand. According to the data of the land use change survey for Changwu
County in 2008, the pasture land covered 2320.353 hm2, the natural grassland ranked second with
876.087 hm2, and the improved grassland occupied the smallest area with merely 3.007 hm2. On the
basis of formula (3), the water demand quota for alfalfa obtained by Huamin Qiu et al. at four experimental spots (Huachi, Xifeng, Tonwei, Dingxi) in Gansu are taken as the reference data [9], and then modified with temperature and precipitation in Changwu County to calculate the
ecological water demand of grassland in Changwu County as 10.31726 million m3.
Garden-land Water Demand
According to the data of the land use change survey for Changwu County in 2008, the garden-land
covered 8853.933 hm2, including 99.50% of orchards; specifically, apples occupied a dominant
position in gardening and fruit industries. Therefore, by reference to the previous findings, apple’s whole phenological water demand is taken in place of the water demand of all garden-lands in the county in the calculation of the garden and fruit water demand. Through formula (3), the
garden-land water demand of Changwu County is calculated to be 42.36607 m3.
Industrial and Domestic Water Demand
According to the industrial water consumption quota standard of Shaanxi Province, and the specific
situations of Changwu County, the industrial water consumption quota/RMB 10,000 is 12.25m3,
and water consumption quotas for urban residents and public facilities are 95.00 and
47.76/(L·d-1·person-1). For the rural area, the domestic water consumption quota is
35.00L·d-1·person-1, and the water consumption quota for big livestock and small livestock (pigs,
sheep) are 47.50 and 20.75/(L·d-1·head-1).
Conclusion
In this paper, factors restricting the grain production are analyzed for their rationality in the utilization, and then put into the optimal allocation. In conclusion, (1) The first three factors impacting the total grain production of Changwu County are respectively irrigable area, precipitation and irrigation water amount; (2) Changwu County’s water demand (excluding the
ecological water demand of grassland) is 164.1963 million m3, and its annual utilizable
precipitation is 146.2267 million m3, so there will be a gap for 17.9696 million m3 of water
resources. In fact, Changwu County’s annual water consumption is merely 8.37 million m3
Acknowledgement
This research is sponsored by Yunnan science and Technology Department application of basic research project-Youth project No.2014FD024.
References
[1] L.R. Brown, B. Hailweil. China’s water shortage could shake world food security, R. World Watch. 11.4(1998):10-6.
[2] Xinchun Cao, Pute Wu, Yubao Wang. Analysis on temporal and spatial differences of water productivity in irrigation districts in China, J. Transactions of the Chinese Society of Agricultural Engineering. 28.13 (2012): 1-7.
[3] Zhiyu Xu, Zhenwei Song, Aixing Deng, et al. Regional changes of production layout of main grain crops and their actuation factors during 1981-2008 in China , J. Journal of Nanjing Agricultural University. 1 (2013): 79-86.
[4] Liu Yu, Junbiao Zhang. Analysis on temporal differences in water resources security and grain security in China, J. Resources Science. 32.12 (2010): 2292-2297.
[5] Chenglin Miao, Hong Zhou. Water quality prediction based on a grey model, J. China Rural Water and Hydropower. 2 (2007): 126-128.
[6] Shaanxi Province People's Government. Notification of Shaanxi Province People's Government for Printing and Issuing Industrial Water Consumption Quota in Shaanxi Province, Z. Gazette of the People's Government of Shaanxi Province. 12 (2014).
[7] Yongsong Liao, Ji Huang. Impact of crop structure change on irrigation water demand in the basins of Yellow River, Huaihe River and Haihe River, J. Journal of China Institute of Water. 2.3 (2004): 184-188.
[8] Wenzhao Liu. Dynamic interrelations of crop production, water consumption and water use efficiency, J. Journal of Natural Resources. 13.1(1998):23-27.
