Valipour How do different factors impact agricultural water management ?

This study compares the impacts of different factors on agricultural water management in the Americas in the last 50 years. The number of 18 indexes (as the main and sub-main indexes) was selected to assess agricultural water management based on their importance and other indexes were not studied due to lack of adequate data. Changes in the main indexes in 2011 showed that concurrent values across regions varied according to the nature of the indexes and conditions of the countries. In the next step, the value of area equipped for irrigation/ cultivated area (10th index) was estimated using the other main indexes. As a result, a list of strengths and weakness for agricultural water management in the Americas in the last 50 years was created. However, The only way to meet sustainable development is to learn from past experiences for the improvement of agricultural water management. The desirability of condition for agricultural water management is difficult for Central America (except Belize, which presents a fair status) and it is less than 40% for Greater Antilles (with the exception of Dominican Republic 55%). Guyana is the best country for agricultural water management because its desirability of condition (72%) is more than all the countries in Americas.

sectors such as population, energy, food, and environment, and the interactions among them require reckoning, since future food security and poverty reduction are tightly connected to these factors. Previous researches (see also Calder et al. 1995;Tilman et al. 2002;Viala et al. 2008;Foley et al. 2005) are restricted to smaller areas and cannot be apply to other regions, and some studies did not consider the role of all important indexes for agricultural water management. Thus, the goals of this study were to establish a link among important parameters for agricultural water management field, and to investigate the conditions of irrigation and drainage systems and cultivated crops in the Americas during the last 50 years.

Methodology
Irrigation heavily controls global yield variability (Rezaei et Rahimi et al. 2015). Although irrigation efficiency is a proper index for agricultural water management status, it cannot be increased until the value of equipped area is obtained to encourage farmers to use irrigation systems instead of rainfed agriculture. Designing cropping patterns, microeconomic decisions and allocation of water resources required the assessment of several variables to calculate the amount of equipped area for irrigation percultivated area . However, the lack of adequate data does not allow us to consider all parameters. In this study, ten main indexes were selected using AQUASTAT database (FAO 2013), for the assessment of agricultural water management in the Americas from 1962 to 2011, and their values were checked using WBG database (WBG 2013). The relative error for estimated equipped area were then calculated for the chosen countries based on agricultural water management status. In the next step, eight sub-main indexes (based on less information) were evaluated to generate the cropping intensity in the study area for the past 50 years.

Permanent crops/cultivated area (%)
Crops are divided into temporary and permanent crops. Permanent crops are sown or planted once, and cultivated in the same area for some years wihout the need of being replanted after every harvest. Examples of permanent crops are: cocoa, coffee and rubber. In this category are also included flowering shrubs, fruit and nut trees, and vines; however, trees grown for wood or timber, and permanent meadows and pastures are not part of this category. This index is calculated following the equation: 1 ( 100 ( ) ) permanent crops ha I cultivated area ha = × (1)

Rural population/ total population (%)
Usually the rural population index is obtained by subtracting the number of the urban population from the total population. In practice, the criteria adopted for distinguishing between urban and rural areas vary among countries that can be roughly divided into three major groups depeding on: localities of a specific size; certain minor civil divisions with administrative centres; and minor civil divisions based on a chosen criterion which may include the type of local government, the number of inhabitants or the proportion of the population that is engaged in agriculture. Thus, the rural population estimates in this domain are based on the varying national definitions of urban areas: 1 ( 100 ( ) ) permanent crops ha I cultivated area ha = × (2)

Total economically active population in agriculture/ total economically active population (%)
Part of the economically active population is engaged in or seeking work in agriculture, hunting, fishing or forestry (agricultural labour force). The economically active population refers to the number of all employed and unemployed persons (including those seeking work for the first time). It covers employers, self-employed workers, salaried employees, wage earners, unpaid workers assisting in a family or farm or business operation, members of producer cooperatives, and members of the armed forces. The economically active population is also called the labour force. This index is determined as:

Human development index (HDI)
The HDI ( 4 I ) is a composite statistic of life expectancy, education, and income indices used to rank countries into different tiers of human development.

National rainfall index (NRI) (mm/yr)
The NRI is defined as the national average of the total annual precipitation weighted by its long-term average. The NRI is calculated differently in the Northern and the Southern hemispheres. In the northern hemisphere, the indices are calculated based on the January-December rainfall level; the rainfall indices coincide with the calendar year. In the Southern Hemisphere, crops are planted at the end of a year to be harvested in the first half of the following calendar year. Consequently, the index of a year for a crop harvested in that specific year is calculated based on the amount of rainfall from July of the previous year to June of the year of interest. In fact, this index ( 5 I ) is a type of effective rainfall.

Value added to gross domestic product (GDP) by agriculture (%)
Agriculture corresponds to International Standard Industrial Classification (ISIC) divisions 1-5 and includes forestry, hunting and fishing, as well as cultivation of crops and livestock production. The added value is obtained by calculating the net output of a sector after adding up all outputs and subtracting the intermediate inputs. This index ( 6 I ) is calculated without making deductions for depre-ciation of manufactured assets or depletion and degradation of natural resources.

Irrigation water requirement (mm/yr)
Irrigation water requirement is the quantity of water exclusively from precipitation and from soil moisture (i.e. quantity of irrigation water) required for normal crop production. It consists of the water quantity that will ensure a crop's full water requirement (i.e. irrigation consumptive water use, as well as extra water from paddy fields, for land preparation and protection of plants from salinization, therefore allowing plant growth). This index ( 7 I ) corresponds to net irrigation water requirement.

Percent of total cultivated area drained (%)
This index is the percentage of cultivated area that was drained divided by the area of cultivated land, expressed in percentage.

Difference between NRI and irrigation water requirement (mm/yr)
This index shows water deficit and is determined as:

Area equipped for irrigation to cultivated area (%)
It is the area that is equipped to provide water (via irrigation) to crops. It includes areas equipped for full/partial controlled irrigation, equipped lowland areas, and areas equipped for spate irrigation. Although irrigated area and irrigation potential are better indexes than equipped area, there are more available data on equipped area than on the former. Since difference between irrigated area and equipped area is not significant in most countries; we have selected equipped area index to be used in this study. This index is determined as: area equipped for irrigation ha cultivated are I a ha = ×

Estimation of equipped area
We aimed at finding a link among the following indexes: Therefore, several scenarios were tested to study the effect of each index on the 10 th index. The final function was calculated by two methods using data from 2011:  I  I  I  I  I  f I  f  I  I  I   1 100

Condition of the countries for agricultural water management
The status of all countries were identified using two methods: ( ) Then, the agricultural water management condition of each country was classified as:

Sub main indexes 2.2.1 Surface irrigation (%)
Surface irrigation systems are based on the principle of moving water through the soil by gravity to moisten the soil. They can be subdivided into furrow, borderstrip and basin irrigation (including rice irrigation by submersion). Manual irrigation using buckets or watering cans is also included. Surface irrigation does not refer to the method of transporting the water from the source up to the field, which may be done by gravity or by pumping.

Sprinkler irrigation (%)
A sprinkler irrigation system consists of a method of water distribution through a pipe network that pumps the water by pressure until the sprinkler nozzles from where the water is then sprinkled over the crop, similar to natural rainfall. These systems are also known as overhead irrigation systems.

Localized irrigation (%)
Localized irrigation consists of a water distribution method which uses low pressure to pump water through a pre-determined pipe-network pattern, to be dirchrged, in regulated quantity, directly on to each plant adjacent to the pipe. There are three main categories of localized irrigation: -drip irrigation: drip emitters are used to apply water slowly to the soil surface; -spray or micro-sprinkler irrigation: the water is sprayed on to the soil near individual plants or trees; and -bubbler irrigation: a basin is built around each plant or tree which is flooded with water during irrigation. Micro-irrigation, trickle irrigation, daily flow irrigation, drop-irrigation, sip irrigation, diurnal irrigation are also other names for localized irrigation systems.

Spate irrigation (%)
Spate irrigation (sometimes referred to as floodwater harvesting) is an irrigation practice that uses the floodwaters of ephemeral streams (wadi) and channels it through short steep canals to bunded basins where cropping takes place. A dam is often built in the wadi to to divert the available water from its natural course. These systems are in general characterized by a very large catchment upstream (200-5000 ha) with a ratio of "catchment area : cultivated area" = between 100:1 -10,000:1. There are two types of spate irrigation: 1) floodwater harvesting within streambeds which uses a turbulent channel flow to collect and and distribute the water through the wadi to the crops; cross-wadi dams are constructed with stones, earth, or both, and often reinforced with gabions; 2) floodwater diversion, which diverts the floods -or spatesfrom the seasonal rivers to adjacent embanked fields for direct application. A stone or concrete structure raises the water level within the wadi to be diverted to the nearby cropping areas.

Agricultural water withdrawal (10 km 3 /yr)
This is the annual quantity of self-supplied water withdrawn for irrigation, livestock and aquaculture purposes. It includes water from primary renewable and secondary freshwater resources, as well as over-abstraction of renewable groundwater or withdrawal of fossil groundwater, direct use of agricultural drainage water and (treated) wastewater, and desalinated water.

Conservation agriculture area as percentage of cultivated area (%)
Conservation Agriculture (CA) is an agricultural practice whereby the disturbed area is less than 15 cm wide or 25% of the cropped area (whichever is lowest). AQUASTAT distinguishes between 30%-60%, 61-90% and 91% of ground cover. Ground cover must be measured after planting time, and CA is disregarded when ground cover less than 30%. Rotation must involve at least three different crops, although it is a requirement for CA at this stage. However, AQUASTAT reports whether rotation is being carried out or not.

Percentage of salinized soil per area equipped for irrigation (%)
This is percent of area equipped for irrigation that has become salinized due to mineral buildup caused by inadequate drainage.

Waterlogged Area by irrigation (%)
This is a part of the land that is waterlogged because of irrigation. Waterlogging is when the water table rises and is located under or near the surface, resulting in crop yield decline. Irrigation can contribute to the raising of the level of the aquifers by over-saturating the soil profile due to poor soil aeration. Additional drainage is required when recharge to groundwater is greater than natural drainageto avoid waterlogging.

Cropping intensity in equipped area
This index shows cropping intensity for the temporary and permanent crops that are cultivated in the surface, sprinkler, localized, and spate irrigation areas. According to the Fig. 1, the value of permanent crops to cultivated area is low for North America (< 10%), < 30% for South America (except for Colombia and Ecuador, 48% and 54%, respectively), < 40% for Central America (except for Costa Rica: 57%), and < 50% for Greater Antilles. Although this index can help with allocating water resources to where and when it is required, this index also depends on climate conditions ( According to Fig. 2, the value of rural population to total population is less than 30% for North America and < 40% for South America (except for Guyana, 71%). This index is > 30% for Central America and > 40% for Lower Antilles (except for the Bahamas, 16%, and Dominican Republic, 32%). Previous researches show advantages of rural development on agricultural water management and sustainable agriculture in global scale (Evans et al. 2012). Fig. 3 shows total economically active population in agriculture to total economically active population in 2011.

Evaluation of the main indexes of agricultural water management for 36 countries in 2011
According to the Fig. 3, the value of economically active population in agriculture is less than 20% for North America and Greater Antilles (except for Haiti, 58%) and < 30% for Central America (except for Guatemala, 38%), South America (except for Bolivia, 41%), and Lower Antilles. The effects of proper labour force on water management and improvement of sustainable agriculture have been studied by other researchers (Naiken and Schulte 1976). Fig. 4 shows values of human development index (HDI) in 2011.
HDI value is > 0.900 for North America (except for Mexico, 0.755) and > 0.700 for Greater Antilles (except for Haiti, 0.456) and Lower Antilles. The HDI index, as a weighted measure of the Falkenmark indicator (Falkenmark 1989) of the ability of a population to adapt to water stress, is termed the Social Water Stress Index. According to the Fig. 7, the value of irrigation water requirement is less than 700 mm/yr for the Americas (except for Belize, 793 mm/yr, Paraguay 704 mm/yr, and the USA, 789 mm/yr). Variation of this index can be effected by river basin management (Simenstad et al. 1992 Fig. 9 shows the value of the difference between NRI and irrigation water requirement in 2011. In the Fig. 9, the value of the difference between NRI and irrigation water requirement is > 500 mm/yr for the Americas (except for Canada, 201 mm/yr, and the USA, 150 mm/yr).
The index is known as water deficit and low values of such index indicate a a critical status for water resource management in those countries , Qadir et al. 2007). Fig. 10 shows the value of area equipped for irrigation to cultivated area in 2011 (see also FAO 2011a,b).
According to Fig. 10, the value of equipped areas is < 30% for the Americas (with the exception of Venezuela, 30%). The different aspects of irrigation in agricultural water management such as irrigation efficiency, soil salinity ( showed that pressure on water resources for irrigation will continue to increase until 2050. Fig. 11 is applied to summarize obtained results from Figs. 1-10. The green arrows are favorable indices and the red arrows are unfavorable indices. If we accept the negative role of NRI (5th index) and the difference between NRI and irrigation water requirement (9th index), and the positive role of the other main indexes on equipped area (10th index) based on the Eqs 9 and 10 (with the assumption that reduction of 5th index and 9th index, increases 10th index and increase of the other main indexes, increases 10th index), then we have Fig. 11. For North America, the value of HDI and the difference between NRI and irrigation water requirement are suitable, but the value of equipped area is unsuitable (Fig. 11a). Therefore, the role of the other indexes can be effective on the 10th index for this region. The value of rural population to total population is suitable, but the value of equipped area is unsuitable in Central America (Fig. 11b); which leads to a significant role of the other indexes on the 10th index for this region. In the Greater Antilles, the value of HDI is suitable but the value of equipped area is unsuitable (Fig. 11c). Thus, the role of the other indexes can be expressive on the 10th index in this region. The values of rural population to total population and HDI are suitable, whereas the value of equipped area is not suitable in the Lower Antilles (Fig. 11d); therefore role of the other indexes can be impressive on 10th index in this area. Finally, Fig. 11d shows the values of the all indexes (with the exception of HDI without trend) in South America that are unsuitable; hence, the role of the all indexes can be significant on 10th index for this part of the world. There is a wide range of changes in the effective main indexes on agricultural water management in the Americas, as seen in Figs. 1 to 10. Therefore, if we want to establish a relationship among the indexes, each country should be considered separately.

Estimation of area equipped for irrigation to cultivated area using the other main indexes of agricultural water management
Tables 1 and 2 (using Eq. 8 and Eq. 9, respectively) show estimated functions for value of equipped area in the Americas. A comparison between Table 1 and Table 2 shows that the obtained coefficients for the main indexes are similar in some cases, while different in others. These disparities (or similarities) are correspond to the of Eqs. 8 and 9. The role of the indexes is similar or different depending on which equation (Eq. 8 or Eq. 9) is used. In addition, the comparison of the countries together shows a distinguishable role of each index for an specific country. According to Fig. 12, in North America, the most important parameter is rural population to total population (Canada and the USA), thus confirming the results in Fig. 11a and proves the reliability of Eqs. 8 and 9. According to the Fig.  12, The important parameters for Central America are NRI (for Belize, Honduras, and Panama) and permanent crops to cultivated area (for El Salvador and Nicaragua), and, therefore, support the results presented in Fig. 11b. The indicates permanent crops to cultivated area, I2 indicates rural population to total population, I3 indicates total economically active population in agriculture to total economically active population, I4 indicates HDI, I5 indicates NRI, I6 indicates value added to GDP by agriculture, I7 indicates Irrigation water requirement, I8 indicates percent of total cultivated area drained, I9 indicates difference between NRI and irrigation water requirement, and I10 indicates area equipped for irrigation to cultivated area  most important parameter detected for the Greater Antilles is the value added to GDP by agriculture (for Dominican Republic and Jamaica), which supports the results presented in Fig. 11c. In the Lower Antilles, the most important parameter is the permanent crops to cultivated area index (for Antigua, Barbuda, Saint Kitts and Nevis), thus confirming the results in Fig. 11d Lastly, the parameters that are more important in South America include total economically active population in agriculture to total economically active population index (for Guyana, Colombia, Ecuador, and Paraguay) and the value added to GDP by agriculture index (for Argentina, Chile, and Uruguay). These results also confirm what is depiected in Fig. 11e and proves that the Eqs. 8 and 9 are reliable. Fig. 13 is useable to assess effect of the main indexes on equipped area (10th index) in Americas based on Eq. 8 and Eq. 9.

Prioritization of the main indexes of agricultural water management based on the obtained coefficients for each index
Total economically active population in agriculture to total economically active population, permanent crops to cultivated area, and the value added to GDP by agriculture indexes have a significant effect on the estimation of area equipped for irrigation to cultivated area index (or 10th index), as ooposed to HDI, which has the least impact on the same index (Fig. 13). It is supported by Figs. 11 and 12 and proves that the Eqs. 8 and 9 are reliable., and The index values of total economically active population in agriculture to total economically active population (Figs.  3 and 11), permanent crops to cultivated area (Figs. 1 and  11), and the value added to GDP by agriculture (Figs. 6 and  11) are low; hence, these factors can lead to a reduced propensity of governments and/or farmers to use irrigation systems. Contrarily, the value of HDI is relatively high for the Americas (Fig. 4 and Fig. 11), indicating that this index has a small effect on low values of equipped area for irrigation in the Americas (Figs. 12 and 13). Although equations 8 and 9 have been shown to be reliable in the calculation of the status of agricultural water management, their accuracy was determined by equations 12 to 14.  Table 3 shows calculated errors for suggested functions (Tables 1 and 2) using equations 12 to 14.

Calculation of the error for suggested functions to estimate the value of irrigation index
According to the Table 3, the accuracy of equation 8 is higher than that of equation 9. The values of the mean relative error are < 20% (except for Grenada and Venezuela). Therefore, equations 8 and 9 should be applied for Grenada and Venezuela (Tables 1 and 2) with care due to their estimated errors. However, we can update the formulas in Tables 1 and 2 by using Eqs. 8 and 9, and base the new formula on new data (or only on fc) at the end of any water year. In the next step, total status of the countries for agricultural water management has been studied using the Eqs. 15 and 16. Table 4 presents the total status of the countries in terms of agricultural water management based on the equations 15 and 16.  Table 1 and Table 2 respectively, b and d, number of cases that each index has been introduced as main factor to estimate 10th index (maximum coefficient in each formula) based on Eqs. 8

and 9 respectively
The status of agricultural water management is suitable for Costa Rica, Dominican Republic, Ecuador, Guatemala, Guyana, Mexico, and Venezuela (Bolivarian Republic of Venezuela) and it is fairly for Barbados, Belize, Chile, Colombia, Dominica, Haiti, Peru, Saint Lucia, Saint Vincent and the Grenadines, Suriname, Trinidad and Tobago, United States of America, and Uruguay (Table  4). However, the situation is different in Central America (except for Belize, with a moderate status) and < 40% for the Greater Antilles (except for Dominican Republic, 55%). It is important to highlight that Guyana has the highest status for agricultural water management (72%) among all other American countries. These differences in the statuses of agricultural water management in the American countries are due to nature of equations 15 and 16The funcions used to estimate the equipped area for irrigation (or the 10th index) were applied to all years (when there were available data). However, due to the sparse data for 2011, other aspects were considered for this specific year. Therefore, a more thoroughout study is still necessary to to assess the trend of agricultural water management in the Americas in the last 50 years. Variations of permanent crops to cultivated area index were not significant and the value of NRI varied during the  (Tables 1 and 2), the errors less than 10% show a suitable status, the errors between 10% and 20% show a fairly status, and the errors more than 20% show a difficult status to apply the Eqs. 8 and 9 (the first and the second formulas, respectively)

Country
Relative error in the first formula (%) Relative error in the second formula (%) past fifty years due to various factors such as greenhouse gases (Lal 2001), global warming (Michaels 1990), climate change (Muzik 2002), among others (Fig. 14).According to the Fig. 14, increasing slopes for permanent crops to Cultivated area, HDI, percent of total cultivated area drained, and equipped area are less than decreasing slopes for rural population to total population, total economically active population in agriculture to total economically active population, and value added to GDP by agriculture. It should be noted that, although mechanization and the use of new technologies have an important role in enhancing agricultural knowledge and increasing productivity (Kirpich et al. 1999), rural development and labor force have a vital and irreplaceable role in agricultural development and macroeconomic perspectives (Hendrickson et al. 2008). Other parameters such as possible disadvantages of irrigation systems (the sub-main indexes) have also an effect on agricultural water management. However, a more comprehensive study on these aspects would require further information on the Americans that are not available yet. Fig. 15 shows variations of the sub-main indexes of agricultural water management in the Americas. According to the Fig. 15, the value of conservation agriculture area had a considerable increase whilst the value of waterlogged area decreased due to increases in pressurized irrigation as well as percentage drained area per total cultivated area (Fig. 14). From 1977 to 2002, the value of salinized area increased due to the expansion of agricultural water withdrawal and, consequently, irrigation. During that period, it is possible to see a reduction in agricultural water withdrawal (although this index may increasein case of proper use) and, thereby, in salinized area. From 2007 to 2011, drained areas are continued to increase and the positive effect of such phenomenon is the expansion of localized irrigation systems and their (Schaible and Aillery 2012) considerable impact on water conservation (Ward and Pulido-Velazquez 2008). However, the value of spate irrigation increased, which calls for specific attention to sedimentation risks that may derive from this irrigation system (Embaye et al. 2011).

Figure 14:
Variations of the main indexes for Americas in the past half of century, the left axis is belong to HDI, NRI, irrigation water requirement, and difference between NRI and irrigation water requirement and the right axis is belong to permanent crops to cultivated area, rural population to total population, total economically active population in agriculture to total economically active population, value added to GDP by agriculture, percent of total cultivated area drained, and area equipped for irrigation to cultivated area (value of the HDI is not available before 1982 and values of irrigation water requirement and difference between NRI and irrigation water requirement are not available before 1997) In the final step, cropping intensity (equipped area) has been studied for Americas in the previous half of century.
8 Cropping intensity (equipped area) for Americas in the previous half of century Fig. 16 shows status of cropping intensity (equipped area) in the Americas in the past 50 years.
In the first three decades (1962-1992), a considerable change in cropping intensity could not be detected. During 1992-1997, maize, fodder, and cotton plantation areas increased while those of rice, citrus, grapes, and tea decreased. During this period, irrigation systems were used on growing wheat, barley and, other cereals, as well as vegetables, soybeans, groundnuts, sweet potatoes, leguminous crops, sugar beet, sugarcane, tobacco, flowers, plantains, and other fruits, plus coconut, and rubber (Fig. 15). The increased cropping area demanded an unprecedented increase in agricultural water withdrawal during this period (Bouwer 2002). Between 1997 and 2002, the plantation area for rice, barley, vegetables, soybeans, flowers, citrus, grapes, coconuts, tea, increased and, whereas cropping area for wheat, maize, other cereals, fodder, cotton, groundnuts, leguminous crops, sugar beet, sugarcane, tobacco, plantains, rubber, and other fruits decreased. During those years, irrigation systems were used for cassava, grass and fodder plantations for the first time. These changes led to an increase in irrigation water consessions (Fig. 14) and a significant increase in sprinkler irrigation (Fig. 15) (Winch 2006). From 2002 to 2007 (see also Schaible and Aillery 2012), the area for cultivating wheat, maize, other cereals, vegetables, groundnuts, sugar beet, sugarcane, fodder, cotton, flowers, plantains, grapes, other fruits, coconuts, and teaincreased, and the opposite trend was deected for rice, soybeans, sweet potatoes, cassava, citrus, and grass and fodder. Irrigation systems were being used for sesame and bananas during those years, which also led to a decrease in irrigation water consessions (Fig. 14) and significant increase in pressurized irrigation (Fig.  15) during that period (Colaizzi 2008). From 2007 to 2011, cropping area for wheat, maize, vegetables, soybeans, groundnuts, sesame, sugarcane, cotton, flowers, tobacco, oil palm, and grass and fodder increased, while cultivated land forrice, other cereals, sugar beet, fodder, plantains, bananas, citrus, grapes, other fruits, coconuts and tea decreased. Then, irrigation systems were used for olive and coffee plantations, which led to an increase in the irrigation water requriement (Fig. 14) and to a significant increase in localized irrigation during this period (Fig. 15). Although part of cropping intensity depends on climate conditions (Lobell et al. 2008, Lobell et al. 2011) and on crop rotation (Tilman et al. 2002), trial-and-error policies (whether by governments or by farmers) lead to decreased water use efficiency (WUE) and waste of water resources. For example, during 1997 and 2002, irrigation systems were being used on cassava plantation; then, from 2002 to 2007, their use shifted to banana cultivation for the first time, only to be excluded from cropping intensity (equipped area) in the next periods (Fig. 16). Another example is when irrigation systems were being used for oil palm plantation for the first time from 1967 to 1972 (0.4%). Then, oil palm was excluded from cropping intensity (equipped area) from 1972 to 1982, and re-shifted back to oil palm planting between 1982 and 1987 (0.1%). Oil palm was later excluded from cropping intensity (equipped areafrom 1987 to 2007, when a sudden 4% increase was detected in the subsequent year (Fig. 16). Note that values of water use, per kilogram output and energy value are 2 m3/kg and 0.73 m3/1000 kcal, respectively, for oil palm. While these values are 1.5 m3/kg and 0.47 m3/1000 kcal for cereals and 0.15 m3/kg and 0.49 m3/1000 for sugar beet (FAO 2011b).

Conclusion
The goal of this study was to investigate the status of agricultural water management in the Americas during the last fifty years. A total of 18 indexes (as the main and sub main indexes) were selected to assess agricultural water management of each country based on their relevance and on other indexes that could not be included because of sparse data. The changes in the main indexes in 2011 showed that the values varied significantly across different regions due to the nature of the indexes and the conditions of each country. Sybsequently, the value of area equipped for irrigation to cultivated area (or the10th index) was estimated using the other main indexes. The obtained functions were used to estimate the mentioned index for any year (with a relative error < 20%), to assess the importance of each index for every country and to forecast changes in the 10th index based on variations in the contributing indexes in future years. Prioritization of the main indexes showed that total economically active population in agriculture to total economically active population, permanent crops to cultivated area, and value added to GDP by agriculture had significant effects on the estimation of area equipped for irrigation to cultivated area (10th index). The classification of the countries based on the main indexes showed that Guyana had more desirable conditions (willingness to provide better agricultural water management) for agricultural water management than the other countries. The trend of the main indexes shows that, although mechanization and use of new technologies have an important role in enhancing agricultural knowledge and increasing productivity, rural development and labor force have a vital and irreplaceable role in agricultural planning and macroeconomic perspectives. The analysis of the submain indexes showed that the values of pressurized irrigation and agricultural water withdrawal increased significantly over the period in question. Finally, the findings presented in this study warn against trial-and-error policies in regards of cropping intensity, and recommend the involvement of specialists to help plan approprate irrigation systems according to crop/platation type. The variations in the indice values occurred due to various parameters, such as human activities, climate change, climate variability, global warming, hydrological cycle, greenhouse gas emission, environmental issues, among others. The present study has also allowed us to create a list for the Americans regardling their strengths and weakeness in terms of agricultural water management during the last 50 years. However, the only way to meet sustainable development in these countries is to use past experiences in future agricultural water management plans.