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A sustainable management of global freshwater resources requires reliable estimates of the water demanded by irrigated agriculture. This has been attempted by the Food and Agri- culture Organization (FAO) through country surveys and censuses, or through Global Models, which compute irrigation water withdrawals with sub-models on crop types and calendars, evapotranspiration, irrigation efficiencies, weather data and irrigated areas, among others. Here we demonstrate that these strategies err on the side of excess complexity, as the values reported by FAO and outputted by Global Models are largely conditioned by irrigated areas and their uncertainty. Modelling irrigation water withdrawals as a function of irrigated areas yields almost the same results in a much parsimonious way, while permitting the exploration of all model uncertainties. Our work offers a robust and more transparent approach to estimate one of the most important indicators guiding our policies on water security worldwide.7 ; This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement 792178

AbstractThis paper presents a quantitative analysis of irrigation requirements in different climatic areas of England and Wales. The analysis takes account of the differing requirements of various crops and variation in soil texture. The results include an estimation of irrigation requirement in an average year, a typical dry year for irrigation planning purposes, and an exceptional year such as 1976. The analysis was conducted using a computer programme developed jointly by the Agricultural Development and Advisory Service of the Ministry of Agriculture, Fisheries and Food, together with the Meteorological Office, and a brief description is given of the salient features of the programme.

The purpose of this study was to determine the financial cost of irrigation water in the Jordan Valley and the corresponding impact of higher water prices on farming. The analysis shows that JVA needs significant tariff increases to be able to attain a more financially sustainable footing. In case JVA wants to at least cover its operating and maintenance costs in 2013, it will require JD 0.108 per m3 - assuming that the current cross-subsidies and current inefficiency levels remain unchanged. Yet, if the JVA would be able to reduce its billing and collection inefficiencies, the required irrigation water tariff drops to JD 0.066 per m3. The more efficient JVA becomes in providing irrigation water, the smaller the required tariff increases. The JVA can improve its efficiency by (i) changing billing and collection practices; (ii) change in the revenue policies; and (iii) efficiency gains in the delivery of JVA services. The impact of tariff increases on farmers' incomes is in general very moderate because water costs make up only a small part of the total cost of farming. Certain cropping patterns will be much more affected by the tariff increases than others. It is especially crops that tend to consume large volumes of water (citrus), that will feel the impact of the irrigation water tariffs. Because the agricultural sector in Jordan is under stress, any government policy to rationalize irrigation water subsidies should where possible try to increase the resilience of farmers. The farmer survey found that 17 percent of the survey respondents could be classified as poor for which specific measures may be needed to help them cope with the effect of higher water prices.

Irrigation water shortages have lately been a main area of
concern for policymakers and planners in Pakistan. Current literature on
the country's water resources predicts an alarming situation regarding
the availability of irrigation water in the future due to declining
water tables and serious financial, environmental, and social
constraints of developing big storage reservoirs. Since there is little
room to augment water supplies by building new dams, the existing
supply-driven surface irrigation system needs to be replaced by a
demand-based system with special focus on water use efficiency through
the introduction of an appropriate water pricing system. The present
study aims to evaluate several alternative water pricing systems in the
search for choosing one that will ensure efficient use of irrigation
water in Pakistan. A related objective is to test the extent of
sensitivity of the demand for irrigation water to a change in
alternative water prices. A major conclusion that emerges from this
research is that irrigation water shortages are the result of the
inflexibility of the present irrigation water supply system for
agricultural use and have little to do with the existing water pricing
practice in the country. Furthermore, the results of our water price
simulations exercise confirm the general perception that demand for
irrigation water is less sensitive to changes in alternative irrigation
water prices. Two findings from the pricing policy perspective are: (i)
irrigation water is not available in adequate quantity to farmers in the
nine sub-districts surveyed at almost all of the alternative prices in
Pakistan's irrigated agriculture sector since the predicted water usage
at all prices is greater than the actual usage for all districts; and
(ii) our empirical analysis indicates significant inefficiency of
resource allocation in respect of irrigation water as shown by its
positively large marginal value product to opportunity cost
ratio.

The deterioration of water quality is a serious concern for a water scarce‐country like South Africa (SA). This article looks at the risks posed by the common practice of using surface waters to irrigate crops, as these are usually contaminated with harmful cyanobacteria and cyanotoxins which can be bio‐accumulated by plants. In addition to cyanotoxins, SA waters are also heavily impacted by other pollutants such as toxic metals, salts and high electrical conductivity. The consumption of food contaminated with cyanotoxins is a growing human health concern for countries like SA which are faced with surface water eutrophication‐related challenges. The country also lacks research on human exposure to cyanotoxins via irrigated crops and regulations to manage cyanotoxins in irrigation water. Such lack of data and policies thus prompts an urgent need for local evidence‐based research to guide policies and guidelines on cyanotoxins in irrigation water, food plants and water used for livestock.

Tunisia is facing increasing competition for water among users due to population and economic growth. Projections show that the water resources will be fully used by 2010. As a result, the opportunity cost of water has risen significantly. In order to cope with potential water shortages, the Tunisian government has undertaken a set of policies and technical measures, such as institutional reforms, improving the efficiency of water delivery network and water pricing policies reforms. It has been observed that cost estimation of water produced and delivered is not transparent. Thus any increase in water price is opposed by farmers. Data is not consistent, making the establishment of a water pricing scheme difficult. Besides, the water authority lacks accurate information on water productivity at farm level leading to asymmetric information on the side of the authorities as well as on the side of the farmers. For a successful reform of the irrigation water pricing policy two conditions have to prevail: i) integration of the accounting system of capital costs with an analytical approach and ii) assessing farmers' willingness to pay for irrigation water. Finally, the implementation of a water rights system could be an alternative to solve the asymmetric information problem and improve the economic efficiency.