Introduction

Nowadays, the shortage of freshwater sources is a global phenomenon related to climatic changes, population growth, urbanization, industrial racing, and economic development. Agriculture is the world's main user of freshwater, with rainfed agriculture accounting for 80% of cultivated land and 60% of crop production (Kina and Ziga 2019). Climatic changes and inadequate water distribution across the canal network have a significant impact on supplies and could result in catastrophic freshwater shortages in the near future (Luo et al. 2015; Devaki and Vinod 2020; Gabr and Fattouh 2020). Irrigation’s main aim is to provide water in the field to keep crop evapotranspiration (ET) going when there is not enough rain. Therefore, irrigation quantity, frequency, and optimization necessitated time-series agro-climatic details like crop evapotranspiration (ET), crop water requirement (CWR), and net irrigation requirement (NIR) are critical for meeting crop demand while preserving water quality, especially in arid and semi-arid regions (Saseendran et al. 2019; Gabr 2021; Sharma and Tare 2021). CWR depends on climate, cropping area and cropping season, type of soil, and crop production rate (Kawy and Darwish 2014; Ahmed 2021; Khaydar et al. 2021). ET is the composite of crop transpiration and soil evaporation. It is a critical factor for irrigation scheduling, water balance, and crop yield (Matthias et al. 2018). The climate parameters, crop characteristics, management and environmental factors affect the evapotranspiration process (Kawy and El-Magd 2013; López-Urrea et al. 2020). There are three types of evapotranspiration: potential, real, and comparison. A crop’s potential evapotranspiration is characterized as soil evaporation and plant transpiration under ideal soil water conditions and actual weather conditions. The maximum rate of evapotranspiration from a broad surface covered fully and uniformly with actively growing plants under conditions of unrestricted soil water availability is referred to as potential evapotranspiration (Gamal and Mohamed 2015; Koudahe et al. 2018). The amount of water transpired by plants and evaporated from the soil surface under actual meteorological conditions as well as non-optimal soil, biological, management, and environmental conditions is referred to as actual evapotranspiration. It differs from the potential evapotranspiration due to soil water shortage or waterlogging, diseases, soil salinity, and low soil fertility (Allen et al. 1998; Manik et al. 2019). Reference evapotranspiration (ETo) is a significant agroecological parameter for climatological and hydrological studies, as well as for irrigation planning and management (Khalil et al. 2015; Mattar 2015). For ETo, the reference surface closely resembles an extensive green grass surface of uniform height, rising vigorously, shading the ground completely, and providing sufficient water. For the reference surface, the FAO expert consultation on the revision of FAO methodologies for crop water requirements, as (Allen et al. 1998) accepted the following unambiguous definition: “A hypothetical reference crop with an assumed crop height of 0.12 m, a fixed surface resistance of 70 s m−1 and a 0.23 albedo”. The 70 s m−1 fixed surface resistance implies a moderately dry surface of soil resulting from about a weekly irrigation process. There are many methods for estimating ETo, but Penman–Monteith (1998) is regarded as a general norm (Allen 1996; Allen et al. 2005). For identifying and estimating reference crop evapotranspiration, this method was recommended as an international standard method. Many studies have looked at the Penman–Monteith-FAO system and the measured ETo using this method from the perspective of its spatial distribution (Song et al. 2010). On the other hand, other methods of calculating ETo were used (Walaa and Eman 2012; Salama et al. 2015; Khalil et al. 2015). Smith (1991) produced CROPWAT 8.0 simulations, which are likewise based on the Penman–Monteith approach and are widely utilized in the field of water management around the world (Khaydar et al. 2021). It is also regarded as one of the most often used tools for the creation of irrigation schedule plans and computing the crop water requirement (Gabr 2021). Egypt is one of the countries that is currently experiencing water shortage, despite its 55.5 km3/year share of the Nile, which is the main source of water for irrigation and other uses. Egypt has reached a state, where the quantity of available water is imposing limits on its national economic development (El-Shirbeny et al. 2015; Omar and Moussa 2016). This position made it difficult for agricultural scientists to properly manage available water supplies while also considering water conservation. In Egypt, several studies were conducted to estimate ETo and model NIR to encourage better agricultural water management under water scarcity conditions. The implementation of agroecological zoning is one way to accomplish this. For the first time in history, Egypt was divided into three administrative agricultural climate zones (Lower Egypt, Middle Egypt, and Upper Egypt) (Khalil et al. 2015; Sherif 2015). More Egypt’s agroecological zoning were proposed by Noreldin et al. 2016a, b, they split the country into seven zones: (1) Alexandria, (2) Demiatte, Kafr El-Sheikh and Dakhlia, (3) El-Behira, and El-Gharbia, (4) El-Minofia, El-Sharkia, El-Kalubia, Giza and El-Fayom, (5) Beni Sweif, El-Minia, Assuit and Sohag, (6) Qena, and (7) Aswan. In light of Egypt’s water scarcity, water requirements for main crops were computed by Ouda et al (2016). Noreldin et al (2016a, b) looked into how to combat harmful climate effects on maize crops. Mahmoud et al (2016) investigated how to control the cultivation of crops with significant water use, like as rice, in current or changing climates. Saher et al (2019) studied the performance of satellite-based actual evapotranspiration products and the assessment of irrigation efficiency in Egypt. They evaluated and applied three remote sensing actual evapotranspiration products (Earth Engine Evapotranspiration Flux (EEFlux) (METRIC-EEFLUX 2021), SSEBop Evapotranspiration monthly product version 4 (Senay et al. 2013), and the MOD16A2 product (Mu et al. 2011) to Egypt’s Nile Delta and Nile Valley. They concluded that in the delivered irrigation water volumes are substantially larger than the projected actual evapotranspiration and the irrigation efficiency is high. However, due to poor irrigation water management in the old cultivated lands of the Nile Delta and Valley, notably incorrect irrigation scheduling, the performance of the canal command area is far from adequate (Gabr 2018a, 2018b, 2019). Water use efficiency in the command area is quite low, ranging from 40 to 55% (MWRI 2017). The objectives of this study are to establish agroecological zones in the old cultivated lands of the Nile Delta and Valley, as well as new reclaimed areas in Egypt's western desert using climate data years 1985 to 2018 for 31 climatic stations to facilitate better irrigation water management under water scarcity conditions. Also, using the FAO.CROPWAT 8.0 model, compute agricultural water demand for important crops and compare it to real water availability. The comparative study reveals the true size of the water gap. It was also attempted to identify irrigation scheduling for the main crops to determine the frequency of irrigation water. To achieve this objective (i) it is reviewed the Penman–Monteith method to estimate ETo, (ii) the FAO- CROPWAT 8.0 software and CLIMWAT 2.0 model (FAO 2021) were used to calculate average monthly ETo based on FAO Penman–Monteith method for 34-year weather data in 31 meteorological stations, (iii) using the Surfer software, monthly ETo maps for Egypt were plotted and compared to previous literature and measured ETo, (iv) a proposed map for Egypt’s agroecological zones was drawn up, and (v) the net irrigation water requirements (NIR) for the main crops cultivated in Egypt agroecological zones were estimated and the irrigation efficiency is computed.

Materials and methods

Study area description

Egypt is located in the northern-east corner of Africa (Fig. 1). The main water resource is the Nile River, which provides Egypt with 55.5 km3 year−1 of water. It has an arid and semi-arid climate, with abundant solar radiation throughout the year, rare precipitation, and a high ETo rates. The ground surface elevations range from about (− 400 to 2500 m) from the average sea main level. Egypt has a total area of around one million km2, of which only a small amount (8% of the total territory) is arable soil, and the majority of the region is desolate desert. More than 100 million inhabitants, who are mainly concentrated in the Nile Valley and the Delta as well as in the north coastal zone along the Mediterranean Sea, occupy almost 97% of arable land area. Egypt comprises five physiographical areas with unique resource base features, climatic characteristics, soil and geomorphological characteristics, state of land cover and land use, and socioeconomic impacts (Hassan et al. 2019). These five physiographic areas are the Eastern Desert, Western Desert, North West Coast, Sinai Peninsula, and Nile Valley and Delta. Egypt soil types include alluvial soils in the Delta and Valley, desert soils in the Eastern and Western Deserts, calcareous soils along the Egyptian coast, and soils in the Sinai Peninsula (Hassan et al. 2019).

Fig. 1
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Map of territories in Egypt

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Soil and crop data

Soil and crop data were collected to investigate the requirements of crop water in seven Egyptian territories (Delta, Alexandria, Greater Cairo, Suez Canal, North Upper Egypt, Central Upper Egypt, and Upper Egypt) (Fig. 1), covering ten major crops grown (wheat, berseem clover, dry beans, tomato, cotton, rice, sugar beet, potatoes, sugar cane, and maize) in these territories cultivated areas. Crop and soil data in the various territories were collected from the guide to agricultural operations in Egypt by MALR (2020), field observations, and interviews with farmers and stakeholders. These data contain the crop variety, the first, and last planting date, first and last harvesting date, applied irrigation practices (field irrigation method, irrigation frequencies and interval, and irrigation application depths), length of plant growth stages, rooting depth (MWRI 2017).

The main alluvial soils were formed from suspended Nile solid matter and dry desert wadies, which were accumulated during flood season. Because of Egypt’s unique environment, sustainable agriculture and food production is reliant on the efficient use of limited water resources to feed an ever-increasing population. Approximately 10 million acres are currently under cultivation, accounting for less than 6% of Egypt's total region. Figure 2 depicts the annual production of Egypt’s major irrigated crop areas (CAPMAS 2018). In addition, modern irrigation systems irrigate about 1 million acres of the existing 10 million acres of irrigated land. With around 3.33 million acres planted each year, wheat is the most important crop in terms of family and national food security, followed by maize (white), berseem clover, and rice. A second group includes sugar beet, tomato, potato, orange, sugar cane, and cotton, each of which covers around 500,000 acres (Fig. 2). Over the last 30 years, the production of rice, wheat, vegetables, and fruit diagrams (in the New Lands) has increased. Cotton and berseem clover, on the other hand, have been rejected. Cropping patterns are largely determined by demand and government incentives, but the total dominance of wheat, maize, rice, and berseem clover demonstrates the need to feed families and farm animals. The old cultivated governorates of the Nile Delta and Valley are made up of 17 governorates. The soil of these governorates is mainly clay (heavy soils) (Hassan et al. 2019; Gabr 2021), Nine governorates are located in the Nile Delta (Alexandria, Damietta, Kafr El-Sheik, El-Dakahlia, El Behira, El-Gharbia, El-Minofia, and El-Sharkia), four governorates located in the center of Egypt (El-Giza, El-Fayom, Beni Sweif, and El-Minia), and four governorates are located in the south (Assuit, Sohag, Qena and Aswan). In addition, eight boarder governorates (New valley, North Sinai, South Sinai, Red Sea, Marsa-Matrouh, Port Said, Ismailia, and Suez) as shown in Fig. 1. Table 1 summarizes the soil parameters and planting and harvesting crop dates in the seven Egyptian territories used in FAO-CROPWAT 8.

Fig. 2
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Development of the main irrigated crop areas in Egypt. (CAPMAS 2018)

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Table 1 Soil parameters and planting and harvesting crop dates in the seven Egyptian territories used in CROPWAT 8
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Other data

Table 2 summarizes the details of the other pertinent data used in modelling. The CROPWAT 8 model was used to compute the optimal crop water need and the best irrigation scheduling.

Table 2 CROPWAT 8 parameters applied to compute the crop water and irrigation requirements
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CROPWAT 8 model

CROPWAT 8.0 is an FAO-developed decision-support computer tool that uses rainfall, soil, crop, and climate data to calculate ETo, crop water requirement (CWR), NIR, and irrigation schedule.

FAO Penman–Monteith equation

The FAO Penman–Monteith equation for measuring ETo is (Allen et al. 1998):

$$ETo = \frac{{0.408 \Delta \left( {R_{n} - G} \right) + \gamma u_{2} \frac{900}{{T + 273}} \left( {e_{s} - e_{a} } \right)}}{{\Delta + \gamma \left( {1 + 0.34\,u_{2} } \right)}}$$
(1)

where: \({\text{ETo}}\): reference evapotranspiration (mm day−1) \(R_{n}\): net Rad (MJ m−2 day−1), \(G\): soil heat flux density (MJ m−2 day−1), T: mean daily air temperature at 2 m height (°C), \(u_{2}\): wind speed at 2 m height (m s−1), \(e_{s}\): saturation vapor pressure (kPa), \({\text{e}}_{{\text{a}}}\): actual vapor pressure (kPa), \({\text{e}}_{{\text{s}}} - {\text{e}}_{{\text{a}}}\): saturation vapor pressure deficit (kPa), ∆, slope vapour pressure curve (kPa °C−1), and \(\gamma\): psychrometric constant (kPa °C−1).

Meteorological data

CLIMWAT 2.0 model contains seven long-term monthly climatic parameters with the coordinates and altitude of the location (FAO 2021). These parameters are monthly maximum and minimum temperature (°C), wind speed (km h−1), mean relative humidity (%), sunshine hours (h), rainfall data (mm), and effective rainfall (mm) for 31 climatic stations distributed in the 25 Egyptian governorates (Gado 2020; FAO 2021). Daily climate data for the selected stations are years 1985 to 2018. Table 3 summarizes the coordinates and altitudes of the modeled 31 climatic stations and Fig. 3 shows the contour map for these 31 climatic stations.

Table 3 Coordinates and altitude of modeled 31 Egyptian climatic stations
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Fig. 3
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Contour map for the Egypt’s 31 climatic stations

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Crop evapotranspiration (ETc)

The main variable for the estimation of crop evapotranspiration (ETc) was ETo (Devaki and Vinod 2020; Gabr 2021). ETc was calculated the value of ETo and crop coefficient (Kc) under standard conditions (unlimited crop growth, sufficient water availability, and disease and pest free crops) (Doria et al. 2006; Sunil et al. 2021). Equation 1 was used to compute the ETc value from ETo and crop coefficient (Kc) (Ewaid et al. 2019).

$$ET_{c} = K_{c} \times ET_{0}$$
(2)

The NIR and gross irrigation requirement (GIR) were calculated by the following equations:

$${\text{NIR}} = {\text{ ET}}_{{\text{c}}} - {\text{R}}_{{{\text{eff}}}}$$
(3)
$$GIR = NIR/\eta$$
(4)

where \(\eta\): irrigation efficiency, which is mostly determined by the parameters of the irrigation method applied and \(R_{eff}\): effective rainfall (mm).

Results and discussion

Reference evapotranspiration (ETo)

For each of the 31 climatic stations, the CLIMWAT 2.0 calculates the meteorological parameters and the CROPWAT 8.0 calculates the ETo (Table 4). Figure 4 shows the mean annual rains in mm, while, Figs. 5, 6 show the monthly ETo maps for the wet seasons (autumn and winter) and dry seasons (spring and summer), respectively. Generally, the higher ETo was recorded in the Middle and Upper Egypt regions. The lowest ETo is 3.04 mm day−1 observed in January and February, being less triple than in July and August. In October, ETo ranges from 4 to 9 mm day−1, in November, ETo ranges from 2 to 6.2 mm day−1, and in December ETo ranges from 1.8 to 5 mm day−1 (Fig. 5). The highest values of ETo more than 5 mm day−1 occur in the driest regions in Egypt that have the lowest rainfall which often less than 30 mm year−1 (Fig. 6). The highest values of the monthly ETo regions during the growing season are located in the Upper part of Egypt where ETo reaches to 9.2 mm day−1 in July and August. The results of ETo are in accordance with results given by Noreldin et al. (2016a, b) and Mohammed and Bassam (2017), which showed that ETo was lowest during the peak of the rainy season to highest during the peak of the dry season for the studied regions. The minimum ETo values are influenced by decreasing air temperature, sun solar radiation hours, and wind speed, as well as increasing relative humidity, and the maximum ETo values are affected by the reverse (Yang et al. 2016).

Table 4 Monthly average metrological parameters and estimated ETo for the modeled 31 stations
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Fig. 4
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Mean annual rainfall for the modeled 31 climatic stations

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Fig. 5
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Mean ETo in autumn and winter

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Fig. 6
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Mean ETo in spring and summer

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Statistical analysis

ETo correlation matrix analysis

For climatological and hydrological investigations, as well as irrigation planning and management, reference evapotranspiration (ETo) is an important agro-meteorological parameter. Table 5 summarizes the correlation relationship between ETo and the weather parameters used to estimate ETo in the 31 climatic stations using Excel program. A strong positive relationship between ETo and solar radiation and potential sunshine hours of correlation coefficients 0.782 and 0.744 respectively was detected. Whereas, a strong negative relationship between ETo and relative humidity was detected (0.844). Both relative humidity and cloudiness have direct inverse associations with ETo, according to his negative correlations. In addition, a weak relationship between ETo and wind speed and minimum temperature were detected.

Table 5 Correlation matrix coefficient between ETo and the weather parameters in the 31 climatic stations
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Agro-ecological zones

Figure 7 shows the average ETo values in Egypt for the 31 stations that were modelled. The average calculated ETo identified five agroecological zones with high ETo values over the summer months of April to September. As shown in Fig. 8, the maximum ETo in the first zone (A) is 8 mm day−1, followed by 7 mm day−1 in the second zone (B), 6 mm day−1 in the third zone (C), 4.5 mm day−1 in the fourth zone (D), and 3.5 mm day−1 in the fifth zone (E).

Fig. 7
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Average ETo in Egypt for the modeled 31 stations

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Fig. 8
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Agroecological zones in Egypt

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NIR modelling for Egypt’s territories

An investigation was undertaken on the requirements of crop water in seven Egyptian territories covering ten major crops grown (wheat, berseem clover, dry beans, tomato, cotton, rice, sugar beet, potatoes, sugar cane, and maize) in these territories cultivated areas. This was due to the desperate attempts made by some farmers across the country to use the water resources at their disposal to grow crops, especially horticultural crops with a high value market. For each of the territories selected for CROPWAT 8 analysis based on data about cultivated area is according to CAPMAS 2018. Crop and soil data in the various territories were collected from the guide to agricultural operations in Egypt by MALR (2020), field observations, and interviews with farmers and stakeholders. These data contain the crop variety, the first, and last planting date, first and last harvesting date, applied irrigation practices (field irrigation method, irrigation frequencies and interval, and irrigation application depths), length of plant growth stages, rooting depth (MWRI 2017).

Crop water requirement for Delta territory

Wheat, fully grown bean (dry beans), potatoes, sugar beet, berseem clover, maize, tomato, cotton, and rice were the main crops considered in the Delta territory. The estimated ETo values varied greatly among these crops, as shown in Table 6. berseem clover had the highest ETo value (823.5 mm), while dry beans had the lowest (402.6 mm). Tomato, berseem clover, potatoes, wheat, cotton, maize, sugar, and beet had 530.7, 823.5, 507, 475.8, 760.5, 487.5, and 585.6 mm, respectively. The crop evapotranspiration values for the nine crops were 178.6, 626.1, 513.2, 318.4, 178.2, 813.3, 576.2, 419.2, and 1,144.1 mm for dry beans, tomato, berseem clover, potatoes, wheat, cotton, maize, sugar beet, and rice, respectively.

Table 6 Main crop water use for Delta territory
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Rice had the highest net irrigation water rwquirment of 3973.8 MCM (million m3), while dry beans had the lowest at 28.8 MCM. This result shows that there is more demand for soil moisture by sugar beet and rice than by the seven crops which had comparable irrigation water requirements. Therefore, total net irrigation requirement for crops were 6255.6 MCM.

Crop water requirement for Alexandria territory

The major crops covered in the Alexandria territory were wheat, dry beans, potatoes, sugar beet, berseem clover, maize, tomato, cotton, and rice. Table 7 summarizes the findings for this territory arising from the CROPWAT 8 analysis. The berseem clover crop indicated the highest value of reference evapotranspiration (1001.3 mm) and the bean crop the lowest (489.5 mm). Cotton, sugar beet, potatoes, wheat, tomato, maize, and rice gave 867.8, 712, 578.5, 578.5, 645.3, 556.3, and 667.5 mm, respectively. The crop evapotranspiration values for the nine crops were 258.6, 956.8, 559.4, 678, 405.3, 257.2, 752.2, 646.7, and 1247.1 mm for dry beans, cotton, sugar beet, berseem clover, potatoes, wheat, tomato, maize, and rice, respectively.

Table 7 Crop water use for Alexandria territory
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Consequently, the net irrigation water requirement for rice was the highest 863.1 MCM and the lowest one is for dry beans 51.7 MCM. The values for the rest of the crops were 133.9, 142.2, 186.9, 207.3, 491.5, 601.5, and 757.1 MCM for cotton, sugar beet, berseem clover, potatoes, wheat, tomato, and maize, respectively. This shows that there is more demand for soil moisture by maize and rice than by the seven crops which had comparable irrigation water requirements. Therefore, total net irrigation requirement for crops were 3435 MCM.

Crop water requirement for Greater Cairo territory

Wheat, dry beans, potatoes, sugar beet, berseem clover, maize, tomato, cotton, and rice were among the major crops grown in Greater Cairo. The results of the CROPWAT 8 study for this territory are summarized in Table 8. The berseem clover crop had the highest reference evapotranspiration value (972 mm), while dry beans had the lowest (475.2 mm). Cotton, sugar beet, potatoes, rice, maize, and tomato wheat gave 842.4, 712, 561.6, 648, 540, 578.5, and 645.3 mm, respectively. The crop evapotranspiration values for the nine crops were 230.4, 934.4, 502.2, 358.2, 1290, 625.4, 691.9, 221.7, and 731.4 mm for dry bean, cotton, sugar beet, potatoes, rice, berseem clover, maize, wheat, and tomato, respectively.

Table 8 Crop water use for Greater Cairo territory
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Consequently, the irrigation water requirement for tomato was the highest 81.4 MCM and the lowest is for dry beans 0.1 MCM and cotton 0.1 MCM. The values for the rest of the crops were 7.7, 41.7, 49.6, 50, 59.2, and 80.2 MCM for sugar beet, potatoes, rice, berseem clover, maize, and wheat, respectively. This shows that there is more demand for soil moisture by wheat and tomato than by the seven crops which had comparable irrigation water requirements. Therefore, total net irrigation requirement for crops were 370.1 MCM.

Crop water use for Canal territory

Wheat, dry beans, potatoes, sugar beet, berseem clover, maize, tomato, cotton, and rice were among the major crops grown in Canal territory. The results of the CROPWAT 8 study for this territory are summarized in Table 9. The berseem clover a crop has the highest ETo value of 965.3 mm, while the dry beans have the lowest at 467.5 mm. As a result, rice has the highest net irrigation water demand (1539.6 MCM), whereas dry beans have the lowest (9.1 MCM). This shows that there is more demand for soil moisture by wheat and rice than by the seven crops which had comparable irrigation water requirements. Therefore, total net irrigation requirement for crops were 2,862 MCM.

Table 9 Crop water use for Canal territory
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Crop water requirement for North Upper Egypt territory

Dry bean, rice, berseem clover, tomato, potatoes, cotton, sugar cane, maize, sugar beet, and wheat were among the major crops grown in Canal territory. The crop water requirements for the North Upper Egypt territory are summarized in Table 10. The sugar cane crop had the highest ETo value of 2080.5 mm, whereas dry beans had the lowest of 627 mm. The net irrigation water requirement for wheat was the highest 792.2 MCM and the lowest for dry beans 3.3 MCM. This indicates that sugar beet and wheat have a higher demand for soil moisture than the other eight crops with similar irrigation water requirements. As a result, the total net irrigation requirement for crops was 2463.6 MCM.

Table 10 Crop water use for North Upper Egypt territory
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Crop water requirement for Central Upper Egypt territory

Table 11 summarizes the findings for this territory arising from the CROPWAT 8 analysis. The sugar cane crop indicated the highest value of ETo (1974.7 mm) and the bean crop the lowest (595.1 mm). Wheat had the highest irrigation water requirement (410 MCM) while berseem clover had the lowest (6.5 MCM) and the total net irrigation demand for the other crops was 1341 MCM.

Table 11 Crop water use for Central Upper Egypt territory
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Crop water requirement for Upper Egypt territory

Table 12 summarizes the findings for this territory arising from the CROPWAT 8 analysis. The sugar cane crop indicated the highest value of reference evapotranspiration (1974.7 mm) while, the potatoes crop the lowest value (769.6 mm). The irrigation water requirement for sugar cane was highest (2833.6 MCM) and lowest for cotton (2.4 MCM). This indicates that maize and wheat have a higher demand for soil moisture than the other eight crops with similar irrigation water requirements. As a result, the total net irrigation demand for crops was 4309.5 MCM.

Table 12 Crop water use for Upper Egypt territory
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Irrigation efficiency

The annual computed total net irrigation requirement for Delta territory, Alexandria territory, Greater Cairo territory, Canal territory, North Upper Egypt territory, Central Upper Egypt territory, and Upper Egypt territory crops were 6255.6; 3435; 370.1; 2862; 2463.6; 1341; and 4309.5 MCM, respectively, indicating total annual net irrigation requirement of 21,036.8 MCM (about 21 km3) for a total area of 3,159,633 ha (7,523,007 acres). According to Egypt water resources balance by MWRI (2017); CAPMAS (2018); and Gabr (2020) (Table 13) the measured gross irrigation Nile freshwater is 42 km3 year−1, indicating 50% irrigation efficiency, since flood irrigation is Egypt’s most widely used irrigation system.

Table 13 Egypt water resources balance (CAPMAS 2018)
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Conclusion

Rapid urbanization, climatic change, deterioration of water resources, and population increase all necessitate the sustainable uses of water resources for every country. In this study, the reference evapotranspiration (ETo) was computed by the FAO CROPWAT 8.0 model using weather data from 31 weather stations in Egypt during the period from 1985 to 2018. ETo values were used to establish agroecological zones (Fig. 8) in agricultural Egypt territories. The average estimated ETo indicated five agroecological zones: zone A has the greatest ETo at 8 mm day−1, followed by zone B at 7 mm day−1, zone C at 6 mm day−1, zone D at 4.5 mm day−1, and zone E at 3.5 mm day−1. ETo exceeds effective rainfall in much of the country. In addition, the FAO CROPWAT 8.0 model output shows computed net irrigation water requirements (NIRs) for Egypt’s territories Delta, Alexandria, Greater Cairo, Suez Canal, North Upper Egypt, Central Upper Egypt, and Upper Egypt for the major crops (wheat, dry beans, potatoes, sugar beet, berseem clover, maize, tomato, cotton, sugar cane, and rice) of 6255.6; 3435; 370.1; 2862; 2463.6; 1341; and 4309.5 MCM, respectively, suggesting a total net irrigation requirements of 21,036.8 MCM (about 21 km3) for a total cultivated area of 3,159,633 ha (7,523,007 acres). Since flood irrigation is Egypt's most frequently utilized irrigation technology, the observed gross irrigation Nile freshwater is about 42 km3 year−1, implying a computed irrigation efficiency of roughly 50%. Water resources management necessitates the use of modern irrigation technologies and the selection of crop patterns that use the least amount of irrigation water.