Average monthly recharge, surface runoff, and actual evapotranspiration estimation using WetSpass-M model in Low Folded Zone, Iraq

Noor Q. Sabri; Thair S. Khayyun

doi:10.1515/eng-2022-0451

Article Open Access

Average monthly recharge, surface runoff, and actual evapotranspiration estimation using WetSpass-M model in Low Folded Zone, Iraq

Noor Q. Sabri and Thair S. Khayyun

Published/Copyright: November 23, 2023

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From the journal Open Engineering Volume 13 Issue 1

Abstract

The evaluation of the spatial and temporal distribution of groundwater recharge is required to develop the regional groundwater model for more precise simulations of various management scenarios. WetSpass-M (Water and Energy Transfer between Soil, Plants, and Atmosphere under Steady-State Conditions), which is a GIS-based spatially distributed water balance model, is deployed to evaluate monthly groundwater recharge, surface runoff, and actual evapotranspiration in the Low Folded Zone from 2000 to 2019. ArcGIS software prepares the essential relevant input data for the Wetspass-M model as grid maps. They include monthly climatological measurements (precipitation, temperature, and wind speed), land cover distribution, soil map, groundwater depth, topography, and slope. The mean annual groundwater recharge, evapotranspiration, and runoff were found to be 128, 131, and 72 mm, respectively. Accordingly, recharge accounts for 39% of the precipitation, while the rest, 40 and 21%, become evapotranspiration and surface runoff, respectively. WetSpass-M model results are meant to enable integrated groundwater modeling. The study of simulation data demonstrates that the WetSpass-M model accurately simulates the hydrological water budget components of the Low Folded Zone. In addition, a better understanding of the simulated spatial and temporal distribution of water balance components is beneficial for managing and planning the available water resources of the Low Folded Zone in Iraq, which faces water scarcity threats.

Keywords: groundwater recharge; WetSpass-M model; water balance; Low Folded Zone

1 Introduction

Iraq is located in the fastest-warming area in the world, and temperatures have reached as high as 5 4 ∘ C , which is considered one of the highest ever recorded in the Eastern Hemisphere [1]. The country is heavily reliant on the Tigris and Euphrates Rivers as primary freshwater resources, which originate outside the Iraqi border with Turkey. However, due to water policies in Turkey, Iran, and Syria, the discharge rate of these rivers has reduced to less than a third of their normal capacity. In addition, increased water consumption by industries, such as the oil industry, has further exacerbated the situation [2]. Studies have revealed that the quality of fresh water in Iraq has been compromised by an increase in several contaminants [3]. With continuing wars, embargoes, terrorism, and other issues, the exploitation of groundwater resources has become a major focus. Groundwater is a natural resource that holds significant importance that assists in economic growth and environmental sustainability as a component of the hydrologic cycle [4]. It supports ecosystems by saving rivers and stabilizing land in regions with readily compacted soils [5]. Its quantification is essential for the management and utilization of water resources. Although groundwater is diminished mostly through evapotranspiration and surface water bodies, the process of recharging groundwater storage occurs through a hydrologic process [6].

Groundwater can be restored immediately by precipitation, locally by depressions and streams, and implicitly by rivers and irrigation losses [7], urban recharge, and intermediate recharge [8]. Before or after entering surface water courses, some runoff may lead to groundwater recharge through indirect and intermediate processes [9]. The dynamics of groundwater recharge are important to water resource management techniques. This study focuses on the Low Folded Zone due to the lack of understanding of groundwater recharge dynamics despite many research efforts in the region. Inadequate information about recharge dynamics leads to the unsustainable growth of groundwater resources [10]. A crucial aspect for expanding to fulfill the requirements of domestic and farming usage, the water supply is necessary. Due to the increased demand for irrigation water in the Low Folded Zone and the predicted shifts in water extraction toward groundwater, it is recommended that the spatial and temporal distribution of groundwater recharge dynamics be evaluated for their efficient use. Various techniques have been employed to measure the amount of groundwater recharge [11]. Various techniques are available for assessing groundwater resources, including numerical modeling, physical methods, chemical tracing, water balance approaches, streamflow analysis, and so on [12]. Numerical modeling techniques have gained appreciation from researchers for their ability to provide precise, dependable, and swift estimations of groundwater recharge over space and time [13–19].

The presented study is the first work to evaluate the spatial and temporal distribution of water balance components in the Low Folded Zone, Iraq. The groundwater model will be developed using these data, aquifer geometry, and other boundary constraints.

2 Materials and methods

2.1 Study area

Low Folded Zone comprises approximately 13.6% of Iraq’s total land area and has a total area of 5,6930 km 2 . It occupies Iraq’s northern and northeastern central regions (Figure 1(a)). The topography of this Zone’s surface rises in elevation from its Southwestern boundary (125–300 m above sea level) to its Northern and Eastern bounds (900–1,000 m above sea level). The Fatha, Injana, Mukdadiyah, and Bai Hassan Formations, in addition to Quaternary deposits, are the principal aquifers in this region. The Low Folded Zone consists of 13 sub-provinces (Figure 1(a)). The yearly precipitation within the research location is 320 mm.

Figure 1

(a) Location map of the study area and (b) sub-provinces of the study area.

2.2 WetSpass model

Hydrological models are widely used to study hydrological processes across various scales, encompassing models ranging from local watersheds to global scales. However, each model has its own unique set of characteristics, limitations, and potential applications. WetSpass-M (Water and Energy Transfer between Soil, Plants, and Atmosphere under Steady-State Conditions) is a free, ArcGIS-based model simulating runoff, groundwater recharge, interception, and evapotranspiration processes. The WetSpass-M model is available for free download from https://github.com/WetSpass. In this study, the WetSpass-M model calculates the water balance of a grid cell by considering the fractions of bare soil, vegetation, impervious area, and open water. The WetSpass-M model offers numerous benefits, particularly in analyzing long-term spatial patterns of groundwater recharge [20]. The WetSpass-M model has been proven effective in accurately estimating groundwater recharge [21–24]. This study uses the WetSpass model to estimate yearly spatial groundwater recharge. The given equations are utilized to determine the “water balance” components of vegetated, bare soil, open water, and impervious fraction in each raster cell [25].

(1) ET raster = a v ET v + a s E s + a 0 E 0 ,

(2) S raster = a v s v + a S S S + a 0 S 0 + a i S i ,

(3) R raster = a v R v + a S R S + a 0 R 0 + a i R i .

The total evapotranspiration ( ET raster ), surface runoff ( S raster ), and groundwater recharge ( R raster ) of a raster cell are computed based on the vegetated, bare-soil, open-water, and impervious area components ( a v , a S , a 0 , and a i ). The water balance of each component is analyzed and calculated. The water balance of the entire raster cell is computed by starting with precipitation and then analyzing the subsequent processes, such as interception, runoff, evapotranspiration, and recharge, in a logical sequence. This sequencing is necessary to accurately quantify the processes on a seasonal time scale.

2.2.1 Vegetated area

The water balance of the cultivated area is influenced by several factors, including the average monthly precipitation ( P ), the fraction of rainfall that is intercepted by vegetation ( I ), the surface runoff ( S v ), the actual transpiration ( T v ), and the groundwater recharge ( R v ). All these factors are measured in units of length per unit of time, with the following relation [26]:

(4) P = I + S v + T v + R v .

2.2.2 Interception

During the simulation period, the fraction value representing interception depends on the vegetation cover and a predetermined percentage of the annual precipitation value. As rainfall increases, the fraction value decreases since the vegetation cover remains constant.

2.2.3 Surface runoff

To calculate surface runoff, various factors such as the amount of precipitation, precipitation intensity, infiltration capacity, and interception are taken into account, with the initial step being the computation of the potential surface runoff ( S v -pot ) [26] :

(5) S v -pot = C s v ( p − I ) .

Several factors, including soil type, slope, and vegetation cover, determine the coefficient for surface runoff in vegetative infiltration areas ( C s v ). The surface runoff coefficient becomes very high when the area is in groundwater drainage zones. The proximity to the river, vegetation cover, and soil type affect this. While it is often considered to remain unchanged, the actual S v -pot runoff is calculated in the second step by considering the variations of rainfall intensity regarding soil infiltration capabilities [25].

(6) S v = C c h o r S v -pot .

The parameter ( C c h o r ) plays a crucial role in characterizing the seasonal precipitation that adds to the Hortonian overland flow. All precipitation intensities contribute to surface runoff in areas where groundwater discharge occurs. The Cchor parameter is assigned a value of 1.0. Conversely, in infiltration zones, surface runoff is typically generated by storms with high intensities [14].

2.2.4 Evapotranspiration

Two factors must be calculated in seasonal computing evapotranspiration: a reference value for transpiration derived from open-water evaporation and a vegetation coefficient [9].

(7) Tr v = c E o ,

where Tr v is the plant surface’s reference transpiration [ LT − 1 ], E o is the evaporation from open water [ LT − 1 ], c is the vegetation coefficient [ − ] .

Using the Penman–Monteith equation, one can determine the vegetation coefficient as a typical ratio of vegetation transpiration, which estimates the likelihood of evaporation from open water.

(8) c = 1 + γ Δ 1 + γ Δ 1 + r c r a ,

where γ is the constant psychrometric [ ML − 1 T − 2 C − 1 ], Δ is the the first derivative of the saturation vapor pressure curve’s slope (the tendency for saturation vapor pressure at the predominant air temperature) [ ML − 1 T − 2 C − 1 ], r c is the resistance to the canopy [ LT − 1 ], and r a is the resistance in the aerodynamic [ LT − 1 ] provided by.

(9) r a = 1 ( k 2 ) u a ln z a − d z 0 2 ,

where k is the constant of Von Karman − ( 0.4 ) [ − ] , u a is the wind speed [ LT − 1 ] at the measurement level z a = 2 m, d is the zero-plane displacement’s length [L], and z 0 is the vegetation’s or soil’s roughness length [L]. The Penman coefficient ( γ ∕ Δ ), which is temperature-dependent, is shown in Table 1.

Table 1

Variation in Penman coefficient/values as a function of temperature [25]

T(oC)	‒ 20	‒ 10	0	5	10	15	20	25	30	35	40
γ ∕ Δ	5.86	2.83	1.46	1.07	0.76	0.59	0.45	0.35	0.27	0.25	0.17

In areas where groundwater discharge occurs and is covered by vegetation, the actual transpiration ( T v ) equals the reference transpiration since there is no limitation on soil or water availability.

(10) T v = Tr v if ( G d − h t ) ≤ R d ,

where G d is the groundwater’s depth [L], h t is the height of saturated tension [L], and R d is the depth of the rooting [L]. Since the equation yields real transpiration, the groundwater table is lower in farmed areas than in the root zone.

(11) T v = f ( θ ) Tr v if ( G d − h t ) > R d ,

where f ( θ ) is defined as being in a time-variant situation and is a function of water content.

(12) f ( θ ) = 1 − a 1 w T v ,

provided

(13) w = ( p + θ F c − θ p w p ) ,

where a 1 is a calibrated indicator of the sand content of a particular soil type [ − ], W is the amount of water available for transpiration [ LT − 1 ], and ( θ F c − θ p w p ) is the plant’s accessible water content. The variation in water content at field capacity per time step [ LT − 1 ] and the permanent wilting point is the disparity between the water saturation level at field capacity and the point of permanent wilting. It is the amount of water available to plants for each time step.

2.2.5 Recharge

Groundwater recharge refers to water flowing from the water level surface into a saturated groundwater zone. The model calculates the long-term average recharge as a spatial variable affected by various factors such as soil texture, land use, slope, and meteorological variables [27]. The model estimates recharge as a residual value in the water balance system. This process involves water moving from surface water into groundwater under the plant roots, known as “Vaduz.” In the WetSpass model, the computation of groundwater recharge R v is achieved by determining the “residual” term in the water balance equation.

(14) R v = p − S v − E T v − I ,

where E T v is the real evapotranspiration [ LT − 1 ]. It is calculated as the total of transpiration ( T v ), evaporation ( E s ) (evaporation from bare soil between vegetation) and surface runoff ( S v ). Using the equations and relationships mentioned earlier, recharge estimates can be obtained spatially by considering various factors, including vegetation type, soil type, slope, groundwater depth, precipitation, potential evapotranspiration, temperature, etc., and wind speed. It is worth noting that even in discharge areas, a small unsaturated zone exists where some recharge occurs. During summer, the potential transpiration from vegetation can be substantial, resulting in negative recharge values in discharge areas. However, in some situations, the low recharge values can be compensated by high winter recharge values.

2.3 The “water balance” of “bare soil, open water,” and impermeable surfaces

Similar to vegetated areas, the water balance for bare soil, open water, and impervious surfaces is estimated using a comparable procedure. The primary contrast is that no vegetation exists in these scenarios, implying no interception or transpiration component. As a result, the ETv is substituted by E s [23].

2.4 Model inputs

Inputs required for the WetSpass-M model include meteorological data, topographical information, land use/land cover, soil texture, groundwater depth, and leaf area index, which can be prepared in ASCII grid format using GIS software like ArcGIS 10.3.1. The model depends on the water balance principle (Figure 2). The final model grid for this study contains 385 rows, 405 columns, and 15,5925 square raster cells. The raster’s cell size (1,500 m length × 1,500 m width). The data used in the model cover the period from 2000 to 2019.

Figure 2

Schematic representation of the modeling process in the WetSpass model.

2.4.1 Topography

A 30 m resolution Digital Elevation Model (DEM) for 2014 is available on the US Geological Survey website (https://earthexplorer.usgs.gov/), obtained from the Aster satellite. The research area’s topographical values vary from 9 to 1,464 m above sea level, with an average elevation of approximately 318.214 m (Figure 3(a)).

Figure 3

Input grid maps used for the WetSpass model. (a) Topographic map, (b) slope map, (c) soil textural map, and (d) LU/LC map of the Low Folded Zone.

2.4.2 Slope

Using ArcGIS, the slope map is derived from the DEM obtained from the Aster satellite with a 30 m resolution for 2014. The slope map ranges from 1 to 64%, with a mean value of 3.9 and a standard deviation of 4.16. Figure 3(b) shows the slope map of the Low Folded Zone. The area’s topography plays a vital role in determining most of the hydrological processes of the WetSpass spatially distributed hydrological model.

2.4.3 Soil texture

Soil textural information is crucial in the WetSpass model for quantifying recharge. To acquire soil data in this research, the FAOUNESCO (http://www.fao.org) soil map of the world, the soil textural map of the Low Folded Zone, was extracted using ArcGIS software by clipping the digital soil map of the world. A vector dataset at a scale of 1:5,000,000 was digitized and used for this purpose. The case study’s dominant soil textures are clay-D, Clay-loam -D, loam- D, Sand-B, and Sandy-loam-c (Figure 3(c)).

2.4.4 Land use and land cover

Obtaining a land-use/land-cover map is essential for determining the distribution of vegetation and its influence on water balance components from Sentinel-2, 10 m pixel size of raster using the following link: https://www.arcgis.com/apps/instant/media/index. Seven types of land use/land cover are identified in the study area: water, trees, flooded vegetation, crops, built area, bare ground, and rangeland (Figure 3(d)).

2.4.5 Groundwater depth

Classifying the groundwater table’s location is crucial for measuring recharge since shallow groundwater can experience significant evapotranspiration, especially in wetlands dependent on groundwater [20]. To run the WetSpass model, the groundwater table map is one of the necessary inputs.

Therefore, data for Wells have been gathered from The Ministry of Water Resources and the General Commission for Groundwater in Iraq. The groundwater depth for the study area ranges from 1 to 99 m (Figure 4).

Figure 4

Spatial distribution of groundwater depth.

2.4.6 Precipitation

Figure 5(a) displays the average monthly rainfall (in mm) from 2000 to 2019. In the Low Folded Zone, the rainy season lasts 8 months, beginning in the latter half of October and ending in May. Occasionally, there may be some rainfall in October, but it is generally scarce. Precipitation is a crucial element of the hydrological cycle, serving as the driving force that leads to water availability and eventually recharges groundwater systems. This is particularly important in dry and semiarid regions, where precipitation is a significant source of groundwater recharge [28]. The average total rainfall was 320 mm per year. Precipitation data were obtained from the Iraqi meteorological organization and Seismicity.

Figure 5

Meteorological data input into the WetSpass model. (a) Precipitation, (b) temperature, (c) wind speed, and (d) potential evapotranspiration.

2.4.7 Temperature

Low Folded Zone climate is characterized by average temperature degrees ranging from 4.5°C in January (the coldest month) to 33°C in July the (hottest). The 12 temperature maps from January to December. for the study area region from 2000–2019 are shown in Figure 5(b). Temperature data were obtained from ERA5-Land monthly averaged data from 2000 to 2019 [29].

2.4.8 Wind speed

The 12 maps of the average wind speed from January to December from 2000 to 2019 are shown in Figure 5(c). Wind velocity is a climatic factor that impacts the potential evaporation amount. It eliminates the air saturated with a moisture layer and replaces it with dry air, thus facilitating continuous evaporation. Wind data were obtained from ERA5-Land monthly averaged data from 2000 to 2019 [29].

2.4.9 Potential evapotranspiration

Thornthwaite’s method (1984) is used to compute potential transpiration evaporation precisely. It considers the monthly average temperatures and the available data for modifying the daytime radiation hours, making it more appropriate for the study area than other methods. The 12 maps of the average potential evapotranspiration from January to December from 2000–2019 (input in WetSpass-M model) are shown in Figure 5(d).

3 Results and discussion

3.1 Validation of WetSpass-M model

The authenticity of results obtained from any hydrological model is a critical aspect that requires validation. In this study, simulated values of the surface runoff components, groundwater recharge, and actual evapotranspiration have been validated against the calculated value of the surface runoff, groundwater recharge, and actual evapotranspiration.

3.1.1 Surface runoff

The soil conservation service – curve number (SCS-CN) method is widely used to calculate the direct surface runoff resulting from a specific rainfall event (Figure 6). Surface runoff ranges as shown in Figure 7.

Figure 6

Flow chart showing methodology to estimate surface runoff by the SCS-CN model.

Figure 7

Average monthly surface runoff, groundwater recharge, and evapotranspiration value estimated in Low Folded Zone, Iraq.

3.1.2 Recharge estimation

The groundwater balance is determined by the water flow entering and exiting an aquifer through a zone budget, such as a drainage basin. The water balance relies on the equivalence of input and output, so any modification to either input or output will change storage ( Δ S ). Groundwater balance can be expressed by the following equation [31]:

(15) ( Δ S ) = Input (R) − Output ( PET + RO + Δ SM ) ,

where R represents rainfall (L), PET represents potential evapotranspiration (L), RO represents runoff (L), and Δ SM represents changes in the moisture content of the soil (L). Groundwater recharge ranges as shown in Figure 7.

3.1.3 Actual evapotranspiration

According to the following criteria, the actual evapotranspiration (AET) is calculated [32]: IF : R > PET c then AET = PET c I : R < PE c then AET = R , where R represents the rainfall (m/year), PET c represents the corrected potential evaporation, and AET represents the actual evapotranspiration. Actual evapotranspiration ranges as shown in Figure 7.

Simulated surface runoff, recharge, and actual evapotranspiration exhibit excellent agreement with validated results by the WetSpass-M model and the calculated surface runoff, recharge, and actual evapotranspiration. The performance evaluation of the WetSpass-M model was made using the statistics indicated in Figures 8, 9, 10, and Tables 2 and 3.

Figure 8

The linear relationship between simulated and estimated surface runoff.

Figure 9

The linear relationship between simulated and estimated groundwater recharge.

Figure 10

The linear relationship between simulated and estimated actual evapotranspiration.

Table 2

Model’s performance rating is based on the RSR [30]

Performance rating	RSR
Very good	0 ≤ RSR ≤ 0.5
Good	0.5 ≤ RSR ≤ 0.6
Satisfactory	0.6 ≤ RSR ≤ 0.7
Unsatisfactory	RSR > 0.7

Table 3

Performance evaluations for the wetspass-model output parameter

WetSpass-M model	R 2	RMSE	RSR	Performance
Surface runoff	0.97	1.86	0.08	Very good
Groundwater recharge	0.96	3.72	0.1	Very good
Actual evapotranspiration	0.9	3.89	0.088	Very good

3.2 Temporal and spatial distribution of simulated water balance components

WetSpass-M model produces monthly raster maps of surface runoff, actual evapotranspiration, groundwater recharge, and an interception from 2000 to 2019. Each pixel on the map represents a distinct value of the water balance component [23]. This is the first study to assess water balance components’ spatial and temporal distribution in the Low Folded Zone, Iraq. The temporal and spatial monthly surface runoff, recharge, and actual evapotranspiration values, which the WetSpass-M model simulated, are shown in Table 4 and Figures 11, 12, 13.

Table 4

Monthly simulated water balance components by WetSpass model in Low Folded Zone

Month	Water balance components (mm)	Min	Max	Range	Mean	STD
	Rainfall	3.06	98.21	95.15	54.55	26.69
Jan	Evapotranspiration	0.53	15.69	15.16	2.66	1.85
	Runoff	0	94	94	18	12
	Recharge	0	68.17	68.17	31.08	13.41
	Rainfall	5.36	97.99	92.63	50.98	27.69
Feb	Evapotranspiration	5.39	26.59	21.2	10.33	2.28
	Runoff	1	90	89	16	13
	Recharge	0	54.59	54.59	21.66	12.86
	Rainfall	10.19	84.17	73.98	45.83	22.275
Mar	Evapotranspiration	7.8	114.13	106.33	15.31	4.4
	Runoff	0	79	79	11	11
	Recharge	0	47.12	47.12	16.96	11.368
	Rainfall	13.43	63.04	49.61	35.2	14.14
Apr	Evapotranspiration	3	202	199	23	15
	Runoff	0	57	57	2	5
	Recharge	‒ 25	19.19	‒ 5.81	9.15	3.67
	Rainfall	3.73	28.09	24.36	14.71	6.89
May	Evapotranspiration	2	311	309	11	21
	Runoff	0	23	23	0	2
	Recharge	‒ 91.74	12.77	‒ 78.97	5.23	2.14
	Rainfall	0.02	32.92	32.9	5.29	11.3
Jun	Evapotranspiration	0	352	352	5	32
	Runoff	0	23	23	0	1
	Recharge	‒ 185.5	12.8	‒ 172.7	2.03	2.3
	Rainfall	0	34.85	34.85	5.23	12.344
Jul	Evapotranspiration	0	363	363	6	35
	Runoff	0	25	25	0	1
	Recharge	‒ 215.26	13.28	‒201.98	2.01	2.59
	Rainfall	0	33.04	33.04	4.83	11.76
Aug	Evapotranspiration	0	356	365	6	36
	Runoff	0	23	23	0	1
	Recharge	‒ 220.06	12.14	‒207.92	1.84	2.59
	Rainfall	0.0485	27.87	27.82	4.72	9.488
Sep	Evapotranspiration	0	332	332	5	30
	Runoff	0	20	20	0	1
	Recharge	‒ 177.28	10.1	167.18	1.8	2.1
	Rainfall	3.29	25.13	21.84	15.193	5.083
Oct	Evapotranspiration	1	231	230	10	17
	Runoff	0	20	20	1	2
	Recharge	‒ 82.8	12.68	70.12	4.866	2.22
	Rainfall	7.61	60.73	53.12	37.305	14.966
Nov	Evapotranspiration	12	56	44	23	4
	Runoff	0	50	50	5	5
	Recharge	0	21	21	8	5
	Rainfall	4.65	82.22	77.57	48.17	24.1594
Dec	Evapotranspiration	0	21	21	9	2
	Runoff	1	80	79	16	12
	Recharge	0	47	47	21	10

Figure 11

(a–l) Spatial distribution of average monthly Surface runoff simulated by WetSpass model in Low Folded Zone, Iraq.

Figure 12

(a–l) Spatial distribution of average monthly groundwater recharge simulated by WetSpass model in Low Folded Zone, Iraq.

Figure 13

(a–l) Spatial distribution of average monthly actual evapotranspiration simulated by WetSpass model in Low Folded Zone, Iraq.

The monthly surface runoff (mm/month) is estimated using a rational method in the applied WetSpass-M model through an actual surface runoff and soil moisture coefficient. The monthly surface runoff estimation ranges from 0 mm to a maximum of 90 mm, averaging 5.4 mm/month. The average monthly surface runoff ranges from 18.47 mm in January to 0.1 mm in June, July, August, and September. This month they have yielded a small surface runoff value due to the little rainfall. High monthly surface runoff is observed in the northeast locations of the Low Folded Zone because of higher rainfall values. At the same time, the southeast part, which receives less precipitation, has a lower surface runoff, as shown in Figure 11. These locations of the Low Folded Zone hydrogeological sub-provinces are Sinjar–Rabee’a, Kirkuk–Hawija–Tuz Khurmatu, Khazir–Gomel, Dohuk–Alqosh, Altun Kupri, Dibiga, Makhmour, Cham Chamal–Qadir Karam–Qara Too, Erbil, West Tigris River, Kalar–Khanaqeen, Qara Tapa–Al-Sa’adiyah, and Mandali–Zurbatiyah–Teeb.

Simulating the average monthly groundwater recharge from 2000 to 2019 is essential for groundwater management, as shown in Figure 12. Results show that 38% of the total average precipitation is due to average groundwater recharge. The average monthly groundwater recharge ranges from 31.21 mm in January to 2.1–2.43 mm in June, July, August, and September.

Due to seasonal variations, the simulated monthly long-term actual evapotranspiration of the Low Folded Zone varies between 2.69 and 23.38 mm, with a mean value of 10.86 mm (Table 3 and Figure 13).

4 Conclusion

Monitoring groundwater is crucial in the Low Folded Zone as overexploitation is leading to a decrease in its availability. To manage groundwater resources sustainably and improve the flow of rivers and streams, it is important to understand the spatial and temporal variations of groundwater in the region. Accurate simulation and management of the aquifer require studying groundwater balance components. The WetSpass-M model was used to estimate monthly groundwater recharge, actual evapotranspiration, and surface runoff in the Low Folded Zone. Digital maps of specific input data were created using GIS tools, and the WetSpass-M model parameter attribute tables were adjusted to reflect the local environmental conditions.

The monthly surface runoff falls between 0 and 18.5 mm in the study area. Over a long-term period, the yearly surface runoff ranges up to 72 mm. and the percentage of surface runoff is 21% of the average monthly precipitation
The monthly groundwater recharge in the study area varies from 0 to 31.21 mm, representing 39% of the average monthly precipitation, and the annual groundwater recharge ranges up to 128 mm.
The actual evapotranspiration equals 40% of the average monthly rainfall. Over a long-term period, annual evapotranspiration ranges up to 131 mm.
The WetSpass-M model is highly accurate in estimating surface runoff, groundwater recharge, and evapotranspiration, as indicated by both statistical parameters ( R 2 and RSR).
The variations in soil type, land use and cover, topography, and meteorological data within the Low Folded Zone of Iraq are responsible for the changes in the water balance elements.

Funding information: The authors state no funding involved.
Conflict of interest: The authors state no conflict of interest.
Data availability statement: Most datasets generated and analyzed in this study are given in this submitted manuscript. The other datasets are available on reasonable request from the corresponding author with the attached information.

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Received: 2023-03-11

Revised: 2023-04-20

Accepted: 2023-04-30

Published Online: 2023-11-23

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/eng-2022-0451

Keywords for this article

groundwater recharge; WetSpass-M model; water balance; Low Folded Zone

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