1. Introduction
Water scarcity is growing as a concerning issue in many regions which makes water a vital resource that must be managed sustainably. The United Nations Sustainable Development Goal 6 “Clean Water and Sanitation” is dedicated to water and aims to significantly increase global water recycling and safe reuse by 2030. In 2012, the European Union recognized the potentiality of water reuse as a solution to the problems of water scarcity and drought [
1].
Germany is one of the countries in Europe with a high-water availability compared to other European countries surrounded by is surrounded by oceans and seas with numerous rivers and lakes running through it. Agriculture still has greater effects on water bodies through substance emissions and alterations to their physical structure. The use of agricultural fertilizers leads to excessive nutrient discharges into water bodies and contributes significantly to nitrate pollution and over-enrichment of nutrients (eutrophication) in rivers, lakes, and seas [
2]. Due to this reason, Germany and other EU countries have taken outstanding advances in managing their hydraulic resources to meet the need of agriculture, industrial, and tourism sectors, as well as the needs of a rising population.
From June 2023 onwards, treated wastewater would be used for irrigation purposes and excess water would be supplied to the households. On this regard, a new regulation on minimum water requirements will be imposed to encourage water use in agricultural irrigation and reduce the water scarcity brought by climate change in the European Union and enable the deployment of water reclamation while promoting the circular economy, protecting the safety of human health and the environment as well [
3].
Germany has several large-scale water treatment plants that provide clean and safe drinking water to its residents. Undoubtedly, traditional wastewater treatment systems have improved the quality of life in urban areas and lowered environmental stress [
4]. For better reusability of water, the most considerable concern is to know the potentiality of wastewater treatment plant and also consider the urban roof water harvesting for how it added economic value to the water users[
5]. Nevertheless, with the potential for recycling wastewater and the nutrients it contains, the goal of improving sustainable resource management in wastewater treatment has become increasingly important [
4].
Different prior research provided a detailed study on water availability, highlighting the depiction of irrigation water requirements, urban water harvesting, and the potential of wastewater treatment plants in assessing water stress scenarios. For addressing the water scarcity issue, a GIS-based study was conducted to determine the potential volume of treated wastewater and afterwards water quality standardized for suitable irrigation [
6]. Jia et al. [
7] focused that the application of GIS techniques to assess the potential of wastewater reclaim in different land use scenarios in the urban areas of Beijing. Ramirez et al. [
8] employed the water-energy-food Nexus approach to analyze the impact of capturing, treating, and repurposing wastewater for irrigation. Jaramillo and Restrepo [
9] represented a discussion on positive and negative impacts of using treated wastewater and proposed “end of ripe” conventional solutions so that the irrigation purposes can be improved. To address this concern, Moseki et al. [
10] utilized the CROPWAT model to determine the reference evapotranspiration rate (ETo), actual evapotranspiration (ETc), irrigation water requirements (IWR), and the effect of irrigation on yield. According to the study of Bilibio and Hensel [
11], water scarcity situations in Germany were analyzed using the FAO-CROPWAT model to calculate effective precipitation, crop evapotranspiration, actual evapotranspiration, and water deficit from 2014 to 2016. Consequently, Surendran et al. [
12] studied crop water requirement of different paddy variety by using CROPWAT model to estimate the climatic water balance and proposed projected water future demand for irrigation, industrial and domestic purposes. The crucial factor in designing irrigation systems is usually determining the effective rainfall to assess the amount of water that should be supplied through irrigation. Bokke and Shoro [
13] compared various rainfall models using small-scale weather data and found that the USDA-SC method resulted in the lowest net irrigation water requirements in water-scarce regions, whereas the dependable rain method resulted in the highest net irrigation water requirements in water-sufficient region.
After estimation of IWR in CROPWAT some of the research articles demonstrated the geo-spatial distribution and some research took remote sensing techniques for analyzing the crop water demand. Feng et al. [
14] applied spatial distribution techniques for planning and managing maize cultivation at various stages of development on irrigated farmlands. Al-Najar [
15] demonstrated the Gaza Strip spatial distribution results of irrigation water needs for Citrus, Almonds, Date palm, and Grapes based on data from 8 weather stations. Bhardwaj et al. [
16] observed the LULC analysis for evapotranspiration differentiation form the district level collected data. But Adamala et al. [
17] assessed NDVI and LULC for calculation of crop evapotranspiration. Actual evapotranspiration (ETc) of wheat crop was estimated using the crop coefficient (Kc) that has relationship with the NDVI outcomes maps and the reference evapotranspiration (ETo). Machine Learning and Multicriteria Analysis used for the modeling and evaluation of reference evapotranspiration. The study of Kadkhodazadeh et al. [
18] employed 6 machine learning techniques named multiple linear regression (MLR), multiple non-linear regression (MNLR), multivariate adaptive regression splines (MARS), model tree M5 (M5), random forest (RF) and least-squares boost (LSBoost). In urban areas, roofs are often the primary choice for collecting rainwater. Farreny et al. [
19] established guidelines for selecting roofs that would optimize the amount and quality of collected rainwater on four types of roofs: clay tiles, metal sheet, polycarbonate plastic, and flat gravel. Maqsoom et al. [
20] examined a Building Information Modeling (BIM) based approach considering the water scarcity that created a 3D building model based on the average roof area and population. The water demand in the nearby city of Ludwigsburg of this proposed study area was evaluated using a method that can precisely predict the pressure on local water resources in Germany on a single building level and can also be scaled to a regional level while maintaining detail [
21].
Therefore, the primary goal of this research is to create a context for the availability of water for irrigation and household use, estimating the potential of water recycling from wastewater treatment plants. Thus, it is necessary to gather the required factors, environmental derivers, and workflow for building wastewater reuse framework to fulfill the goals. The main research questions are as follows:
What is the extent of agriculture irrigation water requirement (IWR) varied according to agro-climate variable in CROPWAT model in different crop life stages?
How is the definition of urban roof catchment surface can yield the volume of water retaining capacity in each roof type?
How to economically compensate the agriculture irrigation and current water supply from WWTP (wastewater treatment plant) by urban roof catchment harvesting capacity?
The following section has detailed the calculation of water requirements, including the collection and preparation of data, the use of the CROPWAT model to determine irrigation water requirements, the calculation of urban water requirements, and the estimation of economic value.
5. Conclusions
To conclude, this research of agriculture and urban water availability is very significant for the whole regional system. All the three objectives are analyzed in a very scientific way to evaluate the ultimate benefit of encountering future water stress situations as a pilot study for all over Germany.
The agriculture water demand simulation in CROPWAT model evaluation showed that the irrigation water demand is very high in Weinstadt municipality all the year round 2022. The comparative parameter study of five weather stations like reference evapotranspiration, effective rainfall, crop water requirements and irrigation water requirements are very higher in the south-western region surrounding the study areas. In addition to, the results from spatial distribution between the crop studies are varied considerably based on their showing to harvesting periods. Wine Grapes needed a very lower amount of irrigation water because of elevated terrain cultivation and substantial amounts of water owing to the grounds. Regional temperatures are also one of the major factors which is suitable for wine yards in the study regions and due to this water evaporated much less in amounts than groundwater recharges. With regards, winter wheat has the highest irrigation water required crop and maize has the medium conditions in both of their active growth stages. The zonal severity of the IWR is also very effective for this region, because this analysis distinguishes the environmental effects. The western part of the study area is more like the urban regions, that’s why water demands in agricultural lands are very severe. Sequentially when the IWR severity had directed to eastern parts of the Weinstadt, lower sensitive areas are observed due to having the green areas edges with.
Another objective signifies the urban water potentiality calculation so that it can be compared with present sources of water supply reductions. By focusing on this idea, there are ten types of CityGML building model roof types observed. In this study, the primary source of urban water harvesting is considered rainfall. The calculated amount of harvested water has the variation. The pitched and flat roofs have the most harvested capacity linked to other types of roofs have medium or less harvesting capacity. This harvested volume of water is potential water which reduced the present supply volume from the WWTPs. This study referred to it as the economic value for the IWR. In addition to the outcomes from analysis, water framework development has been proposed for the municipality and users to be followed. Instead of doing so, a visualization application is developed so that the total idea of protecting future scarcity induced water availability disseminated easily to the user levels in a very interactive manner. Apart from these above-mentioned analyses, there are many crucial factors to be taken care of in the future such as database management and decision clarification. These are as follows:
- ◾
A comparative analysis can be done using various methods in the CROPWAT model. In the depth of effective rainfall, other methods would be checked in CROPWAT models for the water sufficient region like Germany.
- ◾
The snowfall water harvesting could add the more reduced amount of water which will improv the more proficient amount of potential economic water values.
- ◾
The proper survey data on degree of sloping, roof materials and roof covering can have huge impacts on the urban water availability potentials.
Figure 1.
Research area-Weinstadt, Baden-Württemberg.
Figure 1.
Research area-Weinstadt, Baden-Württemberg.
Figure 2.
Percentage of building roof type.
Figure 2.
Percentage of building roof type.
Figure 3.
FME Workbench Workflow for slopped area calculation.
Figure 3.
FME Workbench Workflow for slopped area calculation.
Figure 4.
Visualization workflow for all Geo-spatial layers.
Figure 4.
Visualization workflow for all Geo-spatial layers.
Figure 5.
Spatial Distribution of (a) reference evapotranspiration; (b) crop water requirements & (c) effective rainfall in Weinstadt municipality.
Figure 5.
Spatial Distribution of (a) reference evapotranspiration; (b) crop water requirements & (c) effective rainfall in Weinstadt municipality.
Figure 6.
Spatial distribution of maize IWR- (a) development stage; (b) active growth stage; (c) mature stage; (d) total water requirements.
Figure 6.
Spatial distribution of maize IWR- (a) development stage; (b) active growth stage; (c) mature stage; (d) total water requirements.
Figure 7.
Spatial distribution of wine grapes IWR- (a) active growth stage; (b) mature stage; (c) total water requirements.
Figure 7.
Spatial distribution of wine grapes IWR- (a) active growth stage; (b) mature stage; (c) total water requirements.
Figure 8.
Spatial distribution of winter wheat IWR- (a) development stage; (b) active growth; (c) mature stage; (d) total water requirements.
Figure 8.
Spatial distribution of winter wheat IWR- (a) development stage; (b) active growth; (c) mature stage; (d) total water requirements.
Figure 9.
Agriculture water requirement from CROPWAT model- variation of irrigation water requirement in crop lifecycle.
Figure 9.
Agriculture water requirement from CROPWAT model- variation of irrigation water requirement in crop lifecycle.
Figure 10.
Zonal IWR severity- (a) cultivated lands for maize and winter wheat; (b) wine orchards & (c) final agriculture IWR zonal severity .
Figure 10.
Zonal IWR severity- (a) cultivated lands for maize and winter wheat; (b) wine orchards & (c) final agriculture IWR zonal severity .
Figure 11.
Volume of harvested water in different roof types- (a) flat roof; (b) pent roof; (c) pitched roof; (d) hip roof; (e) half-Hipped roof; (f) mansard roof; (g) pyramid roof; (h) shed roof; (i) mixed form roof; (j) Miscellaneous roof.
Figure 11.
Volume of harvested water in different roof types- (a) flat roof; (b) pent roof; (c) pitched roof; (d) hip roof; (e) half-Hipped roof; (f) mansard roof; (g) pyramid roof; (h) shed roof; (i) mixed form roof; (j) Miscellaneous roof.
Figure 12.
Symbology of roof types with their rainfall water harvesting capacity- (a) very less water harvesting group; (b) less water harvesting group; (c) moderate water harvesting group; (d) high water Harvesting group; (e) extremely high-water harvesting group. (Source of Basemap: Esri Web Map)
Figure 12.
Symbology of roof types with their rainfall water harvesting capacity- (a) very less water harvesting group; (b) less water harvesting group; (c) moderate water harvesting group; (d) high water Harvesting group; (e) extremely high-water harvesting group. (Source of Basemap: Esri Web Map)
Figure 13.
Potential economic irrigation water value.
Figure 13.
Potential economic irrigation water value.
Figure 14.
Percentile of zonal agriculture land sensitivity.
Figure 14.
Percentile of zonal agriculture land sensitivity.
Table 1.
Runoff Co-efficient (Source: [
29]).
Table 1.
Runoff Co-efficient (Source: [
29]).
Roof |
|
RC |
Reference |
Slopping Roof |
Concrete/asphalt |
0.9 |
(Lancaster, 2006) |
Metal |
0.95 |
(Lancaster, 2006) |
0.81-0.84 |
(Liaw & Tsai, 2004) |
Aluminium |
0.7 |
(Ward et al., 2010) |
Flat Roof |
Bituminous |
0.7 |
(Ward et al., 2010) |
Gravel |
0.8-0.85 |
(Lancaster, 2006) |
Level Cement |
0.81 |
(Liaw and Tsai, 2004) |
Table 2.
Volume of total required water in agricultural field of Weinstadt.
Table 2.
Volume of total required water in agricultural field of Weinstadt.
Crop Name |
Area (m2) |
Potential Irrigation Water Requirement (mm) |
Total Water Requirement (m3) |
Maize |
3,750,000 |
189.00 |
708,750 |
Winter Wheat |
8,750,000 |
223.3 |
195,3875 |
Wine Grapes |
4,700,000 |
60.92 |
286,324 |
Total |
|
2948949 |
Table 3.
Parameters and outputs comparison with previous research.
Table 3.
Parameters and outputs comparison with previous research.
References |
Datasets & Time Frame |
Methodological Philosophy |
Research Methods |
Findings |
Study Regions |
[30] |
Wastewater treatment plant nominal flow rate, soil textures and depth, Land use, DEM; TimePeriod:2009/2010 (Landsat TM imagery), 2000 (Google Earth data and Land use map) |
Analytical Hierarchical Process for Geospatial integration |
Study area characterization by classification, standardizing the sub criteria, Sensitivity analysis and cross validation |
31% of the aquifer is fitting for irrigation, GIS sensitivity ranking cases 1-5. |
Tunisia |
[24] |
Agro Climatic Data, Crop data showing and harvesting; Time Period: 2017-2021 (Agroclimatic data) |
Irrigation water requirement (IWR) and irrigation scheduling for cultivated crops |
CROPWAT Model for calculation of Eto and effective rainfalls, calculation of evapotranspiration |
IWR: 3108.0 mm-Sugarcane, 1768.5 mm- banana, 1655.7 mm- cotton, 402.5 mm - wheat |
Pakistan |
[12] |
Ago-Ecological datasets, Crop data; Time Periods: Not defined |
Total water requirement in various agro-ecological zone in order to estimate ground water balance |
CROPWAT Model 8.0 used to calculation of Evapotranspiration |
Net irrigation requirement: Peddy: 442 to 1483 mm; Water demand: 1146 Mm3 |
India |
[15] |
CROPWAT stations dataset and crops data; Time Period: Not defined |
Irrigation water Requirement estimation for spatial modeling |
CROPWAT Model for crop water requirement and Water qualitative measurements |
IWR: 763 mm/year-Citrus, 722mm/year-Almonds, 1083 mm/year-Date palm, 591 mm/year-Grapes. |
Palestinian |
[14] |
Meteorological Data; Time Period: 1961 to 2001 |
Spatial distribution of crop water requirement |
CROPWAT model for irrigation water requirement and irrigation scheduling, DEM based methods |
Spatial Distribution of ETc of spring maize 324.57-500.55 mm; Water deficit Ratio upto 40% |
China |
[20] |
Daily Rainfall, 2D & 3D model of Building; Time Period: January 2014 – December 2018 (Daily Rainfall) |
Rainwater harvesting assessment through Building Information Modeling (BIM) |
Calculation of potential roofing catchment size, rainwater harvesting potential and fixing of tank capacity |
Collected harvested rainfall water volume: 8,190 L/yr to 103,300 L/yr |
Pakistan |
[21] |
CityGML building Models; Time Period: Not defined |
Urban water demand assessment |
Implementation of water analysis workflow of SimStadt, log-log model for Water demand assessment |
Industrial water demand: 397 to 579 m3 and Predicted precipitation: 248 mm by 2030 |
Germany |
Our Proposed Methodology |
Climate Dataset, Waster water treatment Plant water supply volume, ALKIS Maps Time Period: 1991- 2021 (Temperature, Humidity, Rainfall),1991-2019(Sunshine Hours), 2022 (Wind speed), 2021-2022 (WWTP supply), 2021 (ALKIS maps) |
Agriculture water demand assessment by using the potentiality of urban rainwater harvesting and wastewater treatment plant supply |
Employment of CROPWAT Model for IWR, Zonal severity analysis, Urban roof catchment area measurement, economic value. |
IWR estimation: 189 mm-maize, 22 3mm- winter wheat, 60.92 mm for wine grapes, Spatial Volume of IWR 2948949 m3/yearly. Sensitivity phases 0-5. Rainfall water harvested volume: 864139.075 m3/yearly |
Germany |