1. Introduction
Water scarcity is a serious problem around the world especially in arid regions. These regions face a great challenge due to limited water resources. Among them, Egypt is facing a great challenge due to its limited water resources [
1]. Additionally, a shortage of irrigation water supply from the Nile River is expected after the construction of the Grand Ethiopian Renaissance Dam. Hence, the effective management of these limited water supplies is considered a key consideration for future developments [
2,
3]. Clearly, the agricultural sector is the largest consumer of water resources around the world [
4]. Effective planning and management as well as the sustainable production growth of irrigated agriculture can be achieved in two ways. Either new irrigation projects can be established or existing irrigation systems can be evaluated and their performance can be enhanced [
5,
6]. Recently, improving the performance of irrigation systems proved to be more reliable than establishing new irrigation projects [
7,
8]. The term, ‘‘irrigation water performance (IWP),’’ for various irrigation levels (i.e., field, irrigation system, and basin) was defined as a systematic observation, documentation, and interpretation of the activities relevant to irrigated agriculture [
9]. It can be quantified by factors such as water inflows and outflows, crop water demand, water use, system losses, and crop yield [
7,
10].
Irrigation water performance assessment (IWPA) is the first step toward ensuring sustainable agricultural development and any improvement of the irrigation water management [
11]. The IWPA could be classified into external (EIWPA) and internal (IIWPA) performance assessments [
12]. The EIWPA is related to the overall state of the irrigation system [
13]. It focuses on the water efficiency, environmental impacts, and water productivities of the irrigation system. It can be used to monitor the IWP of the irrigation system over time and to compare the IWPs of different irrigation systems. However, it cannot provide the decision-makers with required information concerning trouble locations and their causes in the irrigation system in order to improve them [
13]. While the IIWPA describes the internal irrigation processes and the water allocation of an irrigation system, it focuses on the comparison of the delivered water supplies and the water demands. It evaluates the temporal and spatial performance variations of the irrigation system using equity, adequacy, efficiency, and dependability indicators [
8]. An adequacy indicator expresses the ability of the delivered water supplies to meet the water demands. An equity indicator measures the fairness of the irrigation water distribution, according to the water demands. Furthermore, a dependability indicator expresses the ability of the irrigation system to deliver the required irrigation water to the water users at the right time [
14]. Recently, the IIWPA was performed around the world to evaluate the internal irrigation processes [
15,
16,
17,
18]. Using both EIWPA and IIWPA is very critical for identifying all of the processes in the irrigation system [
19].
Each IWPA has a different set of indicators. These indicators were introduced in the 1970s to characterize the hydrological behavior of the irrigation schedules using a few understandable numbers [
20,
21,
22,
23,
24,
25,
26]. Several studies have defined the sets of indicators that describe the irrigation water performance [
14,
27,
28,
29]. These indicators were applied to evaluate the existing practices and recommend improvements in both irrigation efficiency and water productivity [
5]. Despite the number of reported irrigation performance indicators, it is necessary to adjust new techniques and approaches to existing management practices. Currently, satellite remote sensing (RS) and the geographic information system (GIS) presented themselves as important tools for providing regional information on the agricultural and hydrological conditions of the land surface [
30]. The first attempt to use remote sensing techniques in irrigation application was in 2006 [
31]. The irrigation efficiency of an irrigation scheme was estimated based on the
ETc derived from the SEBAL algorithm. The IWP of the Gediz basin in Turkey was assessed based on the
ETc derived from the SEBAL algorithm [
32]. The results indicated that the SEBAL algorithm was efficient in assessing the IWP. Moreover, numerous researchers used the
ETc derived from the remote sensing data in assessing the irrigation water performance around the world [
32,
33,
34].
Several studies have reported the IWPA in the Nile delta, Egypt [
35,
36,
37]. An overall “poor” performance of the Nile delta was reported in 2008 by EIWPA using remote sensing techniques and a moderate resolution imaging spectroradiometer (MODIS) with 250 m resolution [
35]. The irrigation water management of old lands in the Nile Delta was assessed at three levels: the main canals, the branch canals, and the on-farm level [
35]. About 53% of the annual irrigation water supply on the main canal level was returned to drainage and saline groundwater sinks. An oversupply of irrigation water and a potential for water savings in the Nile delta was reported by the EIWPA [
35]. Furthermore, a “fair” IWPA for the Nile delta was reported during the summer season of 2008 (from May to October) by using adequacy <0.89 and dependability indicators >0.11 [
37] while a “good” IWPA was reported during the winter season of 2008 (from November to April) using adequacy, dependability, and equity indicators of <0.89, >0.11, and >0.11, respectively [
37].
Despite the number of reported studies, most studies carried out in the Nile delta focused on the EIWPA. However, the IIWPA was not assessed due to the lack of field measurements. Moreover, a framework for both EIWPA and IIWPA has not yet been proposed to assess the irrigation water performance in the Nile delta. Furthermore, the common types of performance indicators for the Nile delta were mainly related to irrigation efficiency, water balance, economic aspects, social and environmental objectives, or system maintenance. However, the equity, adequacy, and dependability indicators are worse than the irrigation efficiency since an insufficient water supply is considered the most critical problem specifically at the ends of the irrigation networks and canals in the Nile delta [
37]. Additionally, previous studies used satellite images with a coarse resolution [
35]. Therefore, there is an urgent need for an updated and more detailed assessment of the irrigation water and its economic return in the Nile Delta. To the best of our knowledge, an assessment of the irrigation water performance in the Nile Delta, using fine resolution remotely sensed data, has not yet been addressed. Hence, the main objective of this study was to provide a comprehensive framework for the irrigation water performance assessment in the Nile delta in terms of both external and internal performances including the agricultural and economic dimensions. This framework consists of the same indicators as those employed in previous studies of the Nile delta in order to compare the IWP over time. Additionally, it uses indicators that were not used before for the Nile delta. Moreover, this study aims to evaluate and update the economic situation of the irrigation water in order to support the decision-makers in managing the water resources. This framework was applied to the Al-Qased canal in the Nile delta as a case study. Additionally, the crop water requirements at a regional scale were calculated by using the Surface Energy Balance Algorithm for Land (SEBAL) model and Landsat 8 images (30 m resolution) to assess the irrigation water performance in the Nile Delta.
4. Conclusions and Recommendations
A comprehensive framework for irrigation water performance assessment (IWPA) based on remotely sensed data was proposed. The framework has two components: The first one is external IWPA (EIWPA) while the second is internal IWPA (IIWPA). The EIWPA indicates the water supply as well as the agricultural and economic performances. On the other hand, the IIWPA expresses the temporal and spatial performances of irrigation water using adequacy (PA), equity (PE), and dependability (PD) indicators. The framework was applied to an irrigation scheme in the Nile delta during the winter season (from November 2015 to May 2016). The crop water requirements were estimated by using the Surface Energy Balance Algorithm for Land (SEBAL) model. Three classes from “good” to “poor” were proposed to classify the EIWPA and IIWPA values. The EIWPA was classified as “poor.” This was due to the oversupply of irrigation water in relation to the crop water requirements. Additionally, the abstraction of groundwater was high in the study area during the winter season. The average water depleted fraction (DF) in the center of the Nile delta showed a potential for a groundwater recharge. The EIWPA assessment emphasized the urgent need to manage the water resources efficiently by reducing the water losses and satisfying the water demands. The economic performance indicated a low net profit of 7.84% of the total crop production. Nevertheless, the net profit of clover production was significantly more efficient than that of wheat (2143 and 1002 LE/hectare, respectively). Therefore, it is recommended that the clover participation should be greater than that of wheat in the winter crop pattern to enhance the economic performance of the irrigation water in the study area. Additionally, it will enhance the water productivity in the study area due to its high CWUE. However, social, environmental, and economic conditions should be taken into consideration in order to increase the clover participation in the winter crop pattern.
The IIWPA at spatial and temporal scales showed a non-uniform distribution of irrigation water between the head and tail branch canals with the right time and quantity manners. Hence, the delivered irrigation water was adequate in the study area during the beginning of the harvesting seasons. However, during the growing season, it was inadequate and not able to meet the crop water requirements. Hence, the groundwater and ADW reuse were used to meet the required irrigation water at the tail branch canals during the growing season.
The overall assessment showed that improving the IWP requires an efficient irrigation water distribution between the branch canals. Additionally, continuous monitoring of this distribution is required. Remote sensing techniques could provide managers with accurate data about the required irrigation water at a regional scale. Therefore, choosing the suitable accuracy and temporal scale of remotely sensed data was a critical issue. The SEBAL model with Landsat 8 images (fine resolution) efficiently provided an accurate ETc distribution along the Nile Delta with R2 = 98%. Thus, the remotely sensed ETc would significantly enhance the accuracy of the IWPA in the study area.