**1. Introduction**

Evapotranspiration (ET) is an essential component of the water cycle that connects hydrologic and biological processes. It is directly affected by water and land management, land-use change and climate variability [1, 2]. Therefore, estimation of ET in vast areas using efficient tools is important for optimum water resources management over different land-use systems [3].

The knowledge of ETa and its spatial distribution can have a great potential to develop new cost-effective indicators of irrigation performance and increase water use efficiency [4]. The ET can be estimated using many methods and techniques

such as lysimeters, sap flow, eddy covariance, Bowen ratio, and scintillometer, which were accurate and efficient at the field scale [5]. However, these techniques cannot be used for large regional scale ET mapping due to prohibitive cost and logistical limitations [6]. Accordingly, remote sensing and biophysical modelling are adequate techniques for evaluating the ET patterns over large scale regions.

SEBAL was selected in this study to estimate the ETa because it can measure the ET without requiring quantifying the other complicated hydrological processes [7]. Also, SEBAL can identify the satellite image's dry and wet pixels by showing a linear relationship between the surface temperature and the temperature gradient difference [8]. The FAO P-M method was adopted to validate the ETa obtained from the SEBAL model, since it used the actual climate data of the study area for quantifying the ETa process.

#### **1.1 Application of LULC systems in hydrology**

The study of land use and land cover (LULC) systems directly affects hydrology at different scales. Many studies showed that the LULC changes have clear impacts on the soil surface runoff, evapotranspiration, groundwater recharge, streamflow, and water balance over agricultural areas.

The impacts of LULC changes on hydrology were investigated in the Loess Plateau of China by Lu et al. [9] using hydrological modelling during the period 1995–2010. There was the transformation of farmland into forests, grassland, and built-up land. They showed slight increases in average annual potential evapotranspiration, actual evapotranspiration, and water yield at the basin scale, but soil water decreased between the two intervals. However, in sub-basins, obvious LULC changes did not have clear impacts on hydrology, and the impacts may be affected by precipitation conditions. The streamflow was also affected by the LULC changes in the Dinder and Rahad Rivers basins located in Ethiopia and Sudan [10]. The LULC of the catchment indicated a significant decrease and increase of the woodland and croplands were observed between 1972 and 2011. The effect of LULC change on streamflow was significant during 1986 and 2011, which could be attributed to the severe drought during the mid-1980s and the recent large expansions of cropland.

The hydrological process of a periurban catchment was quantified using highresolution satellite images (0.50–2.50 m) in the Yzeron district of France [11]. The produced land covers maps of the district categorised into sub-catchments dominated by vegetation and imperviousness areas. According to the image processing and images characteristics, the calculated imperviousness rates were different, and lead to significant differences in the hydrological response. Wolfe et al. [12] compiled climate, geological, topographical, and land-cover data from the Prairie in Canada, and conducted a classification of watersheds using hierarchical clustering of principal components. Their analysis resulted in 7 classes based on the clustering of watersheds. The important defining variables identifying the watersheds clustering were climate, elevation, surficial geology, wetland distribution, and land cover. The authors indicated that developing management strategies is essential to prevent watersheds from future change.

Estimating the actual evapotranspiration and crop coefficients of an almond and pistachio orchard was explored in Central Valley, California, USA during an entire growing season by combining a simple crop evapotranspiration model with remote sensing data [13]. The authors used vegetation index NDVI derived from Landsat-8 to estimate the basal crop coefficient (Kcb), or potential crop water use. Their results showed that the model indicated a difference of 97 mm in transpiration over the season between both crops. However, the soil evaporation accounted for an average of 16% and 13% of the total actual evapotranspiration for almonds and pistachios, respectively. They *Mapping and Assessment of Evapotranspiration over Different Land-Use/Land-Cover Types… DOI: http://dx.doi.org/10.5772/intechopen.96759*

concluded that the combination of crop evapotranspiration models with remotelysensed data helps up-scaling irrigation information from plant to field scale and thus may be used by farmers for making day-to-day irrigation management decisions.

Furthermore, the up-scaling of the daily and seasonally ET using multisource remote sensing images was explored by Cha et al. [14] in the agricultural lands of the Kai-Kong River Basin, Xinjiang, China. They proposed a trapezoidal and a sinusoidal method to upscale daily ET values to seasonal ET. Moreover, the actual ET over LULC types in India's Malaprabha River Basin was estimated using Landsat 8 data and surface energy balance models [15]. Their results demonstrate the challenge in actual ET estimation at a fine spatial resolution and highlight the importance of choosing a suitable algorithm.

#### **1.2 Using of SEBAL model for ET estimation**

The algorithms that use remote sensing products to estimate the energy balance and ET have become increasingly common [16]. Examples of these models are the two-source energy balance (TSEB), developed by Norman et al. [17]; the surface energy balance algorithm for land (SEBAL), formulated by Bastiaanssen (1995); and the mapping of evapotranspiration at high resolution with internalised calibration (METRIC), developed by Allen et al. [18].

SEBAL model is the most widely used algorithm for estimating ET throughout the world that involves applications for agricultural and water resources management, urbanisation impacts, aquifer recharge, and water balances [16].

The SEBAL model applied to determine the distribution of the ETa for analysing water use patterns over a large basin in Kenya [19]. In Indonesia's Java Province, a method was developed using SEBAL to detect and describe the spatial variability of lowland rice ET [20]. The water used to assess irrigation system performance and management was pointed in the Indus Basin, Pakistan, using the ET estimated by SEBAL and MODIS data [21]. Remote sensing and biophysical modelling were used in recent studies to estimate the ET in different Saudi Arabia regions. Mahmoud and Alazba [22] estimated the ETa in the western and southern regions of Saudi Arabia during 1992–2014 using the SEBAL model, MODIS data and field observations. However, the application of SEBAL in Mara Basin of East Africa indicates that the ETa is measurable over different land-use types in data-scarce regions [23]. Daily ET monitoring using SEBAL model also found to be possible for improving water resources decision support over an oasis in the desert ecosystem [24]. The efficiency of the SEBAL model in estimating ET of pistachio crop in the Semnan province of Iran was investigated. The model shows good efficiency for estimating the actual ET of the pistachio product [25]. Moreover, SEBAL was used to calculate ET during the cultivation and harvesting of wheat crops in the Ilam province, Iran [26]. Thus the evaluation using SEBAL and the FAO-Penman–Monteith method showed that SEBAL has sufficient accuracy for estimating ET.

The Kingdom of Saudi Arabia (KSA) suffers a continuing water scarcity and almost around 90% of the agricultural sector's water budget [27]. Groundwater is the primary source of water in the KSA, considering the limited precipitation and high agricultural demands. Moreover, the increased population of Saudi Arabia resulted in a significant increase in water use [28]. Also, the diversity of the LULC in the arid region is critical to water consumption. Accordingly, for effective water resources management in these regions, the impacts of LULC on hydrology need to be assessed. Hence, precise information of the ETa is crucial for policymakers and water planners to develop and formulate strategies for agricultural water utilisation. Therefore, the objective of this study is to assess the potential of Landsat-8 data and SEBAL model for estimating the daily, monthly and annual ETa under different LULC systems in Al-Ahsa region of Saudi Arabia.
