Sustainability of Irrigated Agriculture in Pakistan

Irrigated agriculture has been practiced in the Indus Basin since long, however canal irrigation network along with diversion structures were mainly constructed in the second half of nineteenth and first half of the twentieth century. At present Indus Basin Irrigation System consist of 3 storage reservoirs, 19 barrages, 43 main canals and 12 inter river link canals. The total length of the canal system is more than 60,000 km and over 100,000 canal outlets supply water in cultivated areas. The system was initially designed for low cultivation intensities (average 63% for Punjab), which increased to almost double (120%) due to excessive demand in food and fiber to meet the needs of growing population.

Sustainable development requires that needs of present should be met without compromising on future developments. Sustainability of irrigated agriculture can broadly be grouped into economic, social and environmental sustainability.

Economic Sustainability:

Besides food self-sufficiency, achieving net profit over the long term is the motivating factor that sustains irrigated agriculture. Economically acceptable irrigation systems provide lifestyle and social options for farmers and also contribute to the wider economy and community. To maintain and improve economic acceptability in irrigated agriculture, larger investments are some times required to enhance water availability and increase water use efficiency. The long-term economic sustainability demands that development and management cost need to be assessed and incorporated in the economic analysis to work out the benefit cost ratio.  When the marginal benefit is less than the marginal cost, the irrigation practice loses its economic acceptability, which implies an unsustainable state.

Social Sustainability:

Irrigated agriculture has deep social impacts.  Any change in the policy, management, distribution can cause serious problems. The system should be designed in such a way that it causes least negative social impacts even in the worst scenarios.  The equitable distribution of available resources is the most important thing in this context. The conflicts arise frequently among the people if they are not convinced or properly informed about the system. In countries like Pakistan, where people have generally low temperament, the system need to be designed in such a way that it can facilitate the solution of problems related to irrigation in an efficient way keeping in view the limitation of people behaviors.

Environmental Sustainability:

Water scarcity, pollution, and other water-related environmental and ecological problems have been increasing rapidly in many areas of the world. The environment takes into account the water source, land and air systems that support human production activities.  As water demands in agricultural, municipal, and industrial uses change over time, because of policy and technological changes, among others—the relationship between water use and the environment needs to be continually reviewed and adapted. In river basins where irrigation is the major water use, sustainable water management should ensure a long-term, stable, and flexible water supply to meet crop demands, as well as growing municipal and industrial demands, while at the same time mitigating or preventing negative environmental consequences from irrigation.

A guiding criterion for sustainable irrigation water management is to minimize the interference of the irrigation system with the associated environmental system, including the effects on the water bodies that receive irrigation water through wind-drift, surface runoff, or drainage to groundwater. In addition, to sustain irrigation profit over the long term, irrigation water management must meet legislative requirements with respect to the environment.  Indicators for environmental system integrity fall into three categories:

1. Health of aquatic and floodplain ecosystems. Extensive irrigation can affect drinking water health as indicated by bacteria, nutrients, and toxic contaminants, and soil health as indicated by the soil’s water-holding capacity, total organic Nitrogen and Carbon, PH value, and the conditions of surface aggregates.

2. Water quality. Irrigated agriculture affects water quality in several ways, including higher chemical- use rates associated with irrigated crop production, increased field salinity resulting from applied water, accelerated pollutant transport with drainage flows, groundwater degradation due to increased deep percolation to saline formations, and greater in-stream pollutant concentrations due to flow depletion.

3. Soil degradation. Irrigation is responsible for water logging and salinity in many regions where drainage systems are poor. The irrigation with traditional furrow systems may cause soil erosion that can be measured by the extent of topsoil losses. Thus, the adverse environmental effects of irrigation (such as water logging and salinization, groundwater pollution, and soil erosion) are often cumulative and may develop to an irreversible state because of long-term poor irrigation management. The measure of these indicators should be connected to both the short-term irrigation practices and performances and the long-term dynamic transmissions through some physical processes.

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References

1)      http://talks.php.net/show/top7/20

2)      http://net.tutsplus.com/articles/are-you-making-these-10-php-mistakes/

3)      http://www.sourcerally.net/regin/8-The-PHP-coder%27s-top-10-mistakes-and-problems

4)      http://www.phoenixheart.net/2008/10/six-common-mistakes-in-php/

CANAL WATER MANAGEMENT

Water is under stress with ever growing population, particularly in developing countries with high population growth rates. Recent estimates of the World’s hungry population are 923 million in year 2007 (FAO, 2008). It is expected to be further aggravated as there will be additional 2 billion people by the year 2030 (Gany, 2006). The increased population will enhance the global demand for food accordingly, necessitating efficient management of the irrigated agriculture. To cater for food of the population in 2025, it is estimated that water diversions for irrigation need to be enhanced by 14% to 17% and the food production from the irrigated land needs to be enhanced by 40% (Bos et al., 2005).

Despite the facts that Pakistan has the largest contiguous irrigation system in the world, and that the country has predominantly an agrarian based economy, the conditions in Pakistan are not very promising in terms of meeting the food and fiber demands of its 160 Million population. About 20-34% of its population is still suffering from malnutrition (FAO, 2008). Major causes of lack of food are water shortages due to limited water availability in the system and in-efficient use of the available water (Laghari et al., 2008). Recent years have witnessed shortages of irrigation water of up to 40 % of canal withdrawals. The situation is even worsened due to stalled development of large reservoirs since 1976 (the year of completion of the Tarbela dam). System managers are aware of the situation and started to modernize the century old irrigation system. The basic motivation of the modernization is to rehabilitate the old infrastructure and to enhance the efficiencies to the levels being achieved in other parts of the world. Upper Chenab Canal (UCC) is one of the major canal irrigation systems in Pakistan, facing similar problems of low water application efficiencies, low crop yields and deteriorating irrigation infrastructure. FAO (2002) defines modernization as “a process of rehabilitation of irrigation systems during which substantial modifications of the concept and design are made to take into consideration the changes in techniques and technology and to adapt the irrigation systems to the future requirements of operation and maintenance”. It also requires that the delivery of water should be made as flexible as possible with “demand irrigation being the ideal solution”. First step in this modernization is an in-depth diagnosis of the present performance of the system (FAO, 2002) and to understand the agricultural water demands in temporal and spatial domains (Yoo et al., 2008). The present study will complement the modernization drive in the country.

Historically irrigation water has been applied based on water availability (usually in flood seasons) rather based on crop requirement. Design concept of canal system under study is also the same. Developments of new scientific techniques have enabled the mankind to relate the irrigation demands based on physical parameters such as temperature and evaporation. Several methods can be cited in literature ranging from temperature based methods (such as Blaney Criddle formula), pan evaporation based methods (Hargreaves Class A pan evaporation method) to more complex methods such as radiation-resistance based methods (Penmann-1948 method and its subsequent modifications). Allen (1986) has compared the radiation based methods with the lysimeter readings and found that the Penman-Monteith resistance based model provided the most reliable and consistent daily estimates.

Presently the state of the art methods for estimation of reference evapotranspiration and the crop evapotranspiration are the radiation-cum-resistance based methods and have been recommended by Food and Agriculture Organization (FAO, 1998) and by ASCE’s Task Committee on Standardization of Reference Evapotranspiration (ASCE-ET) (Allen et al, 2005). Both FAO and ASCE-ET utilized Penman-Monteith equation, with a difference of reference crops in each of them. FAO favors a standardized grass of 12 cm heights and ASCE has recommended one short crop (grass) and a tall crop (alphalpha) as the reference crops. Although use of the above two methods in various parts of the World is cited (Allen et al, 2005), but only a couple of studies (Ullah et al., 2001; Laghari et al., 2008) are found for Pakistan region employing this scientific method for estimating evapotranspiration and thus the crop water requirement. Laghari et al. (2008) study does not cover a whole canal system rather is limited to a few wheat fields, while the Ullah et al. (2001) estimated crop water requirements for whole of the Indus Basin Irrigation system. Ullah et al. (2001), however, fell short of estimating the irrigation demands and comparing the estimated irrigation demands with the actual supplies. Present study will fill this gap of estimating the crop water requirement based on ASCE standardized Penman-Monteith (2000) equation, converting it to irrigation demands and then comparing it with the actual water supply for having an insight into possible improvement of a canal irrigation system in Pakistan.

SIGNIFICANCE OF ESTIMATING CROP WATER REQUIREMENTS (CWR)

Crop water requirements are useful in determining when to irrigate and how much water to apply. Evapotranspiration information is needed in determining the volume of water required to satisfy short term and seasonal water requirements for fields, farms and irrigation projects (Burman et al., 1980). Irrigation water requirement is one of the principal parameters for planning, design and operation of irrigation and water resources systems. The incorrect estimation of the irrigation water requirement may lead to serious failures in the system performance and to waste of valuable and scarce water resources. For planning and design purposes, irrigation water requirement has to be studied with respect to the magnitude and variability of the seasonal and peak period irrigation water requirements (Svehlik, 1987). Actual measurements of consumptive use under physical and climatic conditions of any large area are time consuming and expensive. Thus, reliable methods are needed to determine consumptive use. Numerous equations that require meteorological data have been proposed and several are commonly used to estimate ET. The calculation of ET estimates from weather records is appealing because the approach is relatively simple. The calculated reference crop ET can be used to estimate actual ET by using coefficients to account for the effect of soil moisture status, stage of growth and maturity of a crop (Burman et al., 1980). During the planning and design stages it is important to accurately determine the crop water requirements for any irrigation set-up in order to establish whether the source of water can satisfy demand. This is particularly important at peak demand. The crop water requirement figures can used to establish the area that can be irrigated from a given amount of water following a given cropping program. Again costs of delivering water from source to the field can be estimated using crop water requirement figures. [J.M. Makadho and F.Butling, 1987]

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