Assessing the Impact of Climate Change on Irrigation Water Needs Through Conjunctive Water Use: Future Prospectives

Abstract

Over the past two decades, climate change and climatic variability have received significant attention from the scientific community. The present study investigates the impact of future climate change on irrigation water requirements in the coastal districts of Odisha, Eastern India, specifically within the Phulnakhara distributary’s command area of the main Puri canal system. Field investigations were conducted during the kharif and rabi seasons of 2019–2020 and 2020–2021. The study offers a new perspective involving a future climate data-driven model with water requirements of RCP 4.5 for this canal command area, and after integrating this with the optimal cropping area, the optimal future irrigation water needs for the kharif and rabi seasons were determined. The study focused on assessing future irrigation water demands under changing climatic conditions, with an emphasis on the conjunctive use of surface and groundwater resources. Projections indicate that peak irrigation demand will occur in the kharif season of 2042–2043 and the rabi season of 2044–2045. Furthermore, a significant decline in groundwater levels is anticipated, ranging from 1.23 to 1.42 m below ground level (BGL) during the kharif season and from 1.46 to 1.64 m BGL during the rabi season, over the next 30 years (2021–2022 to 2050–2051). The most pronounced groundwater table decline is projected for the years 2042–2043 (kharif) and 2044–2045 (rabi), highlighting the need for sustainable water resource management strategies in the region. Based on this study, integrating the optimal crop area with future irrigation water needs will result in groundwater table fluctuations under the permissible limit.

1. Introduction

The Earth’s climate has undergone a significant transformation since the pre-industrial period, with scientific consensus affirming human-induced climate change as a primary driver of the observed alterations in environmental systems [1]. According to the Intergovernmental Panel on Climate Change (IPCC), anthropogenic greenhouse gas emissions have led to substantial warming of the atmosphere, land, and oceans, with observable consequences such as rising average global temperatures, altered regional precipitation patterns, and an increased frequency of extreme hydrological events like floods and droughts [2,3]. These hydrologic extremes severely influence groundwater recharge dynamics, especially in regions reliant on seasonal rainfall and surface water infrastructure. Future projections indicate that global surface temperatures may increase by 1.1–2.9 °C under low-emission scenarios and by 2.4–6.4 °C under high-emission scenarios by the end of the 21st century (2090–2099), relative to the 1980–1999 baseline [1]. These changes in climate pose significant challenges to water resource management, particularly in areas dependent on both surface water and groundwater for irrigation. Improved knowledge of the effects of climate change on water resources will aid in the formulation of plans for sustainable use and management of these resources. The integration of surface water and groundwater is governed by climate, geology, and surface topology, as well as the ecological quantity and quality of available water.

Due to climate change, extreme events are occurring, e.g., due to the uneven distribution of rainfall, some months receive too much water whereas there are water shortages in the remaining months. The problem of variations in water availability can be overcome by conjunctive water use [4]. As surface water availability becomes more erratic due to altered precipitation patterns, the role of conjunctive water use—an integrated approach utilizing both surface and groundwater—becomes critical to ensuring sustainable irrigation supply and supporting food security [5,6]. The conjunctive use of water is increasingly recognized as a viable strategy to mitigate the effects of climate-induced water scarcity, especially in areas governed by canal systems. This practice allows for the optimization of water availability during seasonal shortages by compensating for canal deficits with groundwater extraction [7]. However, unregulated or excessive dependence on groundwater, especially during dry spells, can lead to long-term aquifer depletion, threatening the sustainability of this approach under future climate scenarios [8]. The conjunctive use of canal water (surface water) and groundwater can mitigate the impact of climate change [9]. In this context, the present study assesses the impacts of climate change at an RCP of 4.5 on conjunctive water resource management in the command area of the Phulnakhara distributary of the Puri Main Canal in Eastern Odisha, India. The area, characterized by a river-fed canal irrigation system, currently possesses substantial groundwater reserves that compensate for surface water deficits during peak agricultural seasons. During the rabi season, the canals do not operate at their maximum capacity, which leaves the command regions unable to meet their entire irrigation demand, leading to poor productivity and cropping intensity [10]. Therefore, it is necessary to use both canal water (surface water) and groundwater. A gap analysis was conducted between projected seasonal crop water demands under future climate scenarios and the current canal water supply. This analysis underscores the vulnerability of groundwater resources to future climatic stressors, including declining recharge rates and increased evapotranspiration, which are expected to reduce groundwater availability and compromise conjunctive water reliability [11].

The integration of groundwater and surface water resources in irrigation planning is a direct contributor to Sustainable Development Goal (SDG) 6, which aims to ensure the availability and sustainable management of water for all. Efficient conjunctive use practices enhance water-use efficiency (SDG Target 6.4), promote sustainable irrigation (Target 6.5), and protect aquifers from over-extraction. Simultaneously, adaptation to climate-induced water scarcity supports SDG 13 (Climate Action), especially Target 13.1, which focuses on strengthening resilience to climate-related hazards. Moreover, ensuring the sustainability of groundwater and preventing land degradation aligns with SDG 15 (Life on Land), specifically Target 15.3, which promotes the restoration of degraded ecosystems and the sustainable use of terrestrial resources.

Recent studies have demonstrated the criticality of integrated water resource management in addressing the compound effects of climate variability and human-induced stressors on groundwater systems [12,13]. For instance, Shah and Mishra [14] highlighted the importance of climate-smart irrigation strategies, including the scheduling of groundwater use during deficit periods, to enhance agricultural resilience. Similarly, Jain et al. [15] emphasized the need for participatory groundwater governance and climate modeling to guide adaptive irrigation planning in eastern India. Given the increasing climate sensitivity of river–canal systems in Eastern India, the implementation of conjunctive water use must be based on sound hydro-climatic forecasting, participatory governance, and technological interventions such as remote sensing and hydrological modeling [16]. The outcomes of this study are expected to inform regional water policy and contribute to adaptive water management strategies that reinforce the sustainability goals outlined in SDGs 6, 13, and 15. The general and specific objectives are as follows:

• To match the supply with the demand for future years through precise assessments of crop coverage and crop water demand.
• To predict the impact of future conjunctive use on the groundwater table declination over the next three decades.
• To provide recommendations for water management strategies based on a data-driven climate model.

The aim is to bridge this research gap by analyzing the effect of climate change on future irrigation demand in the Phulnakhara canal command area under an RCP 4.5 scenario, utilizing the outputs from one of the best-performing GCMs. The anticipated variations in future irrigation water demand and water table declination hold substantial implications for policymakers, providing valuable insights for future irrigation planning and reservoir operation modeling within the command area. By addressing this gap in the literature, this study contributes to the broader understanding of climate change impacts on crop evapotranspiration and irrigation water demand at the command level.

This study offers a novel approach by integrating surface water and groundwater management through an optimization model and a climate model tailored to the specific needs of the Phulnakhara canal command area. It comprehensively analyzed future water table fluctuations in both the cropping seasons, offering critical insights for future water management and policy formulation in the region. Additionally, the use of a data-driven future climate model in forecasting long-term sustainability under changing climatic conditions contributes to the originality of this approach.

2. Research Study Area

The study was conducted from 2019–2020 to 2020–2021 in the Puri main canal system’s Phulnakhara distributary command area, which shares portions of the Cuttack and Khurda districts in Odisha, with a latitude ranging from 20°19′16″ N to 20°14′56″ N and a longitude from 85°52′52″ E to 86°0′0″ E and an elevation ranging from 0 to 29 m above mean sea level (MSL) (Figure 1a–c). The Phulnakhara distributary originates from the Puri main canal system’s Kakatpur branch canal and spans 21.41 km. It has a 4903.29 ha cultivable command area. More than 60% of the canal command area has 1% slope, 35% has 2% slope, and the remaining 5% has a slope of 2–5%. Mostly, the distributary command area is hegemonized by clay and loam soil. The bulk density of the soil ranges from 1.42 to 1.64 gm/cm³. In the research region, there is roughly 1530 mm of yearly rainfall on average. During the kharif season, more than the necessary amount of irrigation water is delivered to the Phulnakhara distributary command area. The canal flow during rabi season is far less than the full supply level, making it impossible to meet crops’ irrigation needs. A sizeable portion of the command region remains fallow since the canal water throughout rabi and the summer is insufficient to meet the crop water demand [17]. This can be overcome by using groundwater resources.

The share of irrigated area in the command area is shown in

Table 1. Share of irrigated area (ha) in the command area.

Sl No.	Name of the Blocks	Kharif	Rabi	Total Irrigated	Total Command Area
1	Cuttack	164.3	116.6	280.9	372.0
2	Baranga	1031.6	553.0	1584.6	2208.2
3	Kantapada	483.4	331.8	815.3	1047.4
4	Bhubaneswar	26.3	8.9	35.2	128.8
5	Balianta	494.5	376.1	870.7	1147.0

, along with the LULC map (Figure 2). The study area includes two blocks of the Khurda district and three blocks of the Cuttack district. Accordingly, the irrigated area in the command area is provided. The crop lands are mainly owned by small and marginal farmers. The crops are generally grown in the kharif and rabi seasons, which can be observed in the LULC map. So, agriculture plays a vital role in boosting the socioeconomic status of the local farmers.

3. Materials and Methods

3.1. Data Requirement and Processing

Various climatic parameters like rainfall, minimum and maximum temperature, and solar radiation on the earth’s surface on daily basis for future years viz. 2022 to 2051, were obtained from the MarkSim Global Climate Model (GCM) at a representative concentration pathway (RCP)-4.5, using the Global Coupled Model-CM3, created at Geophysical Fluid Dynamics Laboratory (GFDL, Princeton, NJ, USA). The sub-division office of the Water Resources Department, Pratapnagari, Govt. of Odisha, provided the daily canal discharge data at the head regulator (HR) of the Phulnakhara distributary, which is used for comprehending the canal delivery schedule and comparing it with the irrigation demand from the optimal cropped area.

The main crops planted in the command region are paddy, various types of vegetable and maize, and chili and ginger in smaller areas during the kharif season. Similarly, the rabi season is used to cultivate summer paddy, wheat, maize, green gram, black gram, gram, field pea, groundnut, sugarcane, potato, other vegetables, mustard, sesamum, sunflower, onion, chili, and turmeric. The optimal part of the study area is presented in

Table 2. Optimal area for different kharif and rabi crops in Phulnakhara canal command area.

Kharif Crops	Optimal Area (ha)
Paddy	2451
Maize	5
Other Vegetables	236
Chili	18
Ginger	2193
Rabi Crops	Optimal area (ha)
Paddy	49
Wheat	0
Maize	3
Greengram	728
Blackgram	403
Gram	3
Field Pea	4
Groundnut	50
Sesamum Til	6
Sunflower	1
Mustard	20
Potato	76
Onion	18
Other Vegetables	649
Chili	48
Sugarcane	22
Turmeric	2824

, which was obtained from the optimization model WinQSB v.2.0 using the area, yield, production, total water requirement, irrigation water requirement, Minimum Support Price (MSP), and cost of cultivation data [18].

3.2. Land Use/Land Cover

The land use and land cover maps of the command area were obtained from the National Remote Sensing Center, Hyderabad. Out of the total ayacut area in the Phulnakhara distributary canal command region, kharif crops and double/triple crops covered 33.88% and 31.45%, respectively. The plantation cover (12.74%), built-up area (9.63%), current fallow (6.77%), rabi crops (3.4%), forest land (0.96%), water bodies (0.60%), and zaid crops (0.42%) were the other categories of land use and land cover in the canal command area (

Table 3. Land use type and their coverage in the study area.

Sl. No.	Land Use/Land Cover	Area (ha)	Area (%)
1.	Built Up	471.97	9.63
2.	Kharif Crop	1661.37	33.88
3.	Rabi Crop	170.09	3.47
4.	Zaid Crop	20.73	0.42
5.	Double/Triple Crop	1542.07	31.45
6.	Current Fallow	331.92	6.77
7.	Plantation	624.66	12.74
8.	Forest	46.92	0.96
9.	Waste Land	4.22	0.09
10.	Water Body	29.34	0.60
11.	Total	4903.29	100.00

and Figure 2).

3.3. Extraction of Climatic Data from GCM

MarkSim, a web-based program, makes use of daily climate data production techniques by downscaling with a user-friendly interface in Google Earth (https://gisweb.ciat.cgiar.org/MarkSimGCM/#, accessed on 20 August 2025), which shows the future climatic parameters for any area of interest on earth. The study area is presented in Figure 3. The International Centre for Tropical Agriculture (CIAT), developed MarkSim, which is a spatially explicit daily weather generator, was made available in 2004 [19]. The MarkSim GCM tool and a similar approach were used to download the future climatic data of Rasulpur Jattan village, situated in Shahpur block of Muzaffarnagar district, Uttar Pradesh, and the future climatic data was analyzed [20]. First, MarkSim computes the daily precipitation, from which it derives weather variables like daily solar radiation and maximum and minimum temperature. By using the monthly means of these variables, it calculates the maximum and minimum daily air temperatures as well as the values of daily solar radiation [21]. In MarkSim GCM, a total of 17 global climate models are accessible. This study chose to acquire future climate data using the GFDL–Global Coupled Model-CM3 for Phulnakhara distributary command area as, amongst the 17 Global Climate Models available in MarkSim GCM, GFDL was the most suitable model for the study, i.e., it was capable of providing an advanced representation of aerosol–cloud interactions, atmospheric chemistry, and land–atmosphere coupling, making it suitable for studying climate change and decadal prediction.

The IPCC designated a trajectory for greenhouse gas concentrations, known as RCP. The IPCC’s 5th Assessment Report (AR5) from 2014 presented four pathways for climate research and modeling. The RCPs—initially RCP 2.6, RCP 4.5, RCP 6, and RCP 8.5—are categorized according to feasible ranges of radiative force in the year 2100 (2.6, 4.5, 6, and 8.5 W/m², respectively) [22,23].

The Global Change Assessment Model (GCAM) team at the Joint Global Change Research Institute (JGCRI) in the United States developed Representative Concentration Pathway (RCP)-4.5, and under RCP 4.5, the long-term radioactive forcing target level is not exceeded and the total radiative forcing level stabilizes soon after 2100 [24]. This is a scenario with medium emissions, where carbon dioxide emissions rise somewhat before beginning to drop about 2040, methane emissions are stabilized, and crop and grassland consumption declines as a result of rising yields and dietary changes. In this scenario, the temperature increases more quickly until the middle of the century and then decreases. A detailed process flow chart of the study is provided in Figure 4, involving the future climatic data in the RCP 4.5 scenario.

3.4. Future Climate Parameters

A graph showing multi-year average future rainfall and temperature is provided in Figure 5. From the graph, it is confirmed that the temperature presents an increasing trend, whereas the rainfall presents an increasing trend until 2034; then, there is a decreasing rainfall until 2051, barring 2047.

3.5. Canal Command Area Irrigation Network

The layout of the Phulnakhara distributary canal command area is provided in Figure 6, where it can be observed that, after its starting point at the Kakatpur branch canal of the main Puri canal system, the distributary fragmented into 5 minor and 29 sub-minor systems. The canal has a design discharge of 6.03 cumec.

3.6. Soil Texture Map of the Irrigation Command Area

The canal command area soil map (1:50,000 scale) was derived from the soil database of NBSS and LUP, Nagpur, India. Two types of soils are predominant in the command area; among them, clay soil (OR151) has the maximum spread area, followed by loamy soil (OR152). The soil types and their extents are presented in

Table 4. Soil types and their extent in the studied command area.

Sl. No.	FAO Soil	Texture	Area (ha)	Area (%)
1.	OR151	Clay	4547.52	92.74
2.	OR152	Loamy	355.77	7.26

and Figure 7. The command area is dominated by hydrologic soil group (HSG) ‘D’, with clayey soil. A small portion of the canal command area is covered with the hydrologic soil group ‘C’, with loamy soil. The CN for HSG ‘D’ is 90 and for HSG ‘C’ is 60–70. The potential retention capacity of the command area ranged from 28 to 169 mm.

3.7. Future Climate Parameter Analysis

The reference evapotranspiration was calculated by the Hargreaves equation involving the future projected temperature and solar radiation data [25]. Though the FAO-56 Penman–Monteith is the recommended standard, the weather parameters required for this method are greater than that of the parameters required in the Hargreaves method. The weather parameters available for future years are lower, so when using the lowest possible parameters, the best-suited method is the Hargreaves method, expressed as follows:

ET₀ = 0.0023 (T_mean + 17.8) (T_max − T_min)^0.5R_a

(1)

where

ET₀ = reference evapotranspiration (mmd⁻¹);

T_max = maximum air temperature for a given day (°C);

T_min = minimum air temperature for a given day (°C);

T_mean = mean air temperature for a given day (°C);

R_a = extraterrestrial solar radiation (mmd⁻¹).

The data on solar radiation observed on the earth’s surface, derived from the MarkSim model, must be transformed into extraterrestrial radiation using the following relationship:

R_s = K (T_max − T_min)^0.5R_a

(2)

where

R_s = solar radiation on earth surface (MJ m⁻² d⁻¹);

R_a = extraterrestrial solar radiation (MJ m⁻² d⁻¹);

K = adjustment coefficient (taken as 0.16 for interior regions where land mass is predominant and air masses are not significantly influenced by large water bodies).

The unit of R_a in Equation (1) is changed from MJ m⁻² d⁻¹ to mm d⁻¹ by multiplying by a conversion factor of 0.408.

3.8. Crop Evapotranspiration

Crop evapotranspiration (ET_c) is determined by the product of the reference crop evapotranspiration (ET₀) and the crop coefficient (K_c) [26].

$${\mathrm{ET}}_{\mathrm{c}}={ \mathrm{K}}_{\mathrm{c}} \text{×}{ \mathrm{ET}}_0$$

(3)

where

ET_c = crop evapotranspiration [mm d⁻¹];

K_c = stage-wise coefficient of crop;

ET₀ = reference crop evapotranspiration [mm d⁻¹].

The parameters of the crop coefficient for the various growth phases, the length of each stage, the planting or sowing date, and the harvesting date for the kharif and rabi crops [27,28] were used to calculate the demand for irrigation water at the HR [29].

3.9. Future Irrigation Water Need for Major Crops

The effects of climate change will cause the agriculture sector’s water demand to change in the upcoming years. Therefore, this industry needs to use water resources efficiently. The estimated ET₀ of future years and the Kc values of the corresponding crops were used to calculate the irrigation water requirements for the key crops cultivated in the Phulnakhara distributary command region. After taking the effective rainfall value and crop water requirements into account, the irrigation water requirement was determined. The U. S. Department of Agriculture’s Soil Conservation Service (USDA SCS) method was used to calculate effective rainfall [30]. The effective precipitation was calculated using the SCS method presented in

Table 5. Calculation of effective rainfall from monthly mean rainfall and mean monthly consumptive use.

Monthly Mean Rainfall, mm	Mean Monthly Consumptive Use, mm
	25	50	75	100	125	150	175	200	225	250	275	300	325	350
	Mean monthly effective rainfall, mm
12.5	7.5	8.0	8.7	9	9.2	10.0	10.5	11.2	11.7	12.5	12.5	12.5	12.5	12.5
25.0	16.2	17.5	18.0	18.5	19.7	20.5	22.0	24.5	25.0	25.0	25	25	25	25
37.5	22.5	24.0	26.2	27.5	28.2	29.2	30.5	33.0	36.2	37.5	37.5	37.5	37.5	37.5
50.0	25	32.2	34.5	35.7	36.7	39.0	40.5	43.7	47.0	50.0	50	50	50	50
62.5	At 41.7	39.7	42.5	44.5	46.0	48.5	50.5	53.7	57.5	62.5	62.5	62.5	62.5	62.5
75.0		46.2	49.7	52.7	55.0	57.5	60.2	63.7	67.5	73.7	75	75	75	75
87.5		50.0	56.7	60.2	63.7	66.0	69.7	73.7	77.7	84.5	87.5	87.5	87.5	87.5
100.0		At 80.7	63.7	67.7	72.0	74.2	78.7	83.0	87.7	95.0	100	100	100	100
112.5			70.5	75	80.2	82.5	87.2	92.7	98.0	105	111	112	112	112
125.0			0.75	81.5	87.7	90.5	95.7	102	108	115	121	125	125	125
137.5			At 122	88.7	95.2	98.7	104	111	118	126	132	137	137	137
150.0				95.2	102	106	112	120	127	136	143	150	150	150
162.5				100	109	113	120	128	135	145	153	160	162	162
175.0				160	115	120	127	135	143	154	164	170	175	175
187.5					121	126	134	142	151	161	170	179	185	187
200.0					125	133	140	148	158	168	178	188	196	200
225.0					At 197	144	151	160	171	182
250						150	161	170	183	194
275						At 240	171	181	194	205
300							175	190	203	215
325							At 287	198	213	224
350								200	220	232
375								At 331	225	240
400									At372	247
425										250
										At 412
450	25	50	75	100	125	150	175	200	225	250

. Here, the effective rainfall is a function of the mean monthly rainfall and mean monthly consumptive use, as shown in Table 5. The crop water demand at the distributary HR was computed by taking the conveyance efficiency (70%) and application efficiency (60%) into consideration [31]. The irrigation water supply for the month and the season was calculated using the daily canal flow release at the HR of the study distributary. Then, a comparison was made between the demand for crop water and supply of irrigation water.

A reduction in precipitation and increase in evapotranspiration cause a reduction in recharge and probably enhance groundwater withdrawal rates. Groundwater recharge depends on the distribution, quantity, and timing of precipitation, as well as evapotranspiration losses. The impact of climate change on water resource availability and conjunctive use, especially in the canal command region, was determined. The irrigation water needs of the optimal cropping pattern were determined. Through using the average of the historical years under consideration as the surface water availability for these years, the groundwater levels in future years were determined.

4. Results and Discussion

Research was carried out on the effects of climate change over the coming 30 years by considering the RCP 4.5 scenario. This scenario was considered as it is the medium-emission scenario (650 ppm of carbon dioxide-equivalent emissions). In the RCP 4.5 scenario, the demand for irrigation water was calculated for various crops, and the average existing irrigation water supply details are presented below.

4.1. Average Existing Supply of Irrigation Water During Kharif and Rabi Seasons

The existing irrigation water supply for 10 years during the kharif and rabi seasons is presented in

Table 6. Existing irrigation water supply for kharif and rabi seasons.

Year	Kharif Irrigation Supply at HR (Mm3)	Rabi Irrigation Supply at HR (Mm3)
2011–2012	32.36	26.38
2012–2013	37.67	0.62
2013–2014	39.99	0.00
2014–2015	38.02	1.04
2015–2016	40.25	0.00
2016–2017	29.83	0.00
2017–2018	34.86	0.00
2018–2019	43.40	1.23
2019–2020	39.48	0.00
2020–2021	38.00	0.00
10 Years Avg	37.39	2.93

. The data was collected from the office of the Assistant Executive Engineer, Pratapnagari Irrigation Sub-Division, Department of Water Resources, Govt. of Odisha. The records provided by the office due presenting the rainfall patterns in this area; for example, in 2011, the rainfall was 1744.9 mm, and the rabi months received more rainfall, leading to high irrigation supply values.

4.2. Determination of Irrigation Water Demand for Kharif Crops

The highest anticipated demand for irrigation water at the HR of the study distributary was predicted in October (1.33 Mm³), followed by November (0.89 Mm³) and July (0.23 Mm³) (

Table 7. Gap between future average irrigation water demand and existing average irrigation water supply on a monthly basis for the kharif season.

Months	Future Irrigation Water Demand at HR (Mm3)	Irrigation Supply at HR (Mm3)	Difference (mm3)
June	0.02	0.04	0.03
July	0.23	0.79	0.56
August	0.00	10.47	10.47
September	0.21	8.50	8.29
October	1.33	11.93	10.61
November	0.89	5.65	4.76
Total	2.67	37.39	34.71

). This highest irrigation demand is primarily due to the critical growth period (maturity to harvesting stage) of paddy, other vegetables, and ginger in October. The amount of water required for irrigation was found to be relatively low in August and June due to the heavy rainfall in these two months. The rain stopped by the end of September, with a significant need for water in October and November [32]. The least amount of water needed for irrigation (almost 0.00 Mm³) was found in August.

4.3. Comparison of Average Existing Irrigation Water Supply with Future Demand for Crop Water During Kharif Season

The maximum average monthly kharif demand for irrigation water, calculated at 1.33 Mm³, was recorded in October, and the lowest was in August (Table 7); in contrast, the HR’s mean monthly kharif irrigation supply was at its peak, i.e., 11.93 Mm³, in October, and 0.04 Mm³ was the lowest level, recorded in June. At the HR, the supply was above the demand for irrigation water during June to November. The difference between irrigation water delivered and future mean monthly kharif irrigation water demand ranged from 0.03 Mm³ in June to 10.61 Mm³ in October. The highest and the lowest irrigation water demand in kharif season was predicted to be 2.78 (2042–2043) and 2.41 Mm³ (2021–2022), respectively, and the groundwater table declination ranged from 1.23 to 1.42 m.

The future irrigation water demand is based on the optimal cropping pattern. Though the irrigation water demand is marginally lower for future kharif periods than the existing 10-year average supply, the canal water in the tail reach of the canal command area is problematic. Farmers used to irrigate their crops using groundwater in the kharif and rabi seasons, as the cost of conveying water to farmers’ fields from the canal is a major issue; this may be the reason for the drop in water availability in the estimates presented in the table [32].

The gap between future irrigation water demand and average existing irrigation water supply for 30 years during the kharif season is presented in

Table 8. Gap between future irrigation water demand and average existing irrigation water supply for the kharif season.

Year	Irrigation Water Demand at HR (Mm3)	10 Years Avg. Irrigation Supply at HR (Mm3)	Difference (Mm3)	Area × Factor	Water Table Fall (m)
2021–2022	2.41	37.39	34.98	19,613.16	1.23
2022–2023	2.59	37.39	34.80	19,613.16	1.32
2023–2024	2.57	37.39	34.81	19,613.16	1.31
2024–2025	2.58	37.39	34.80	19,613.16	1.32
2025–2026	2.59	37.39	34.79	19,613.16	1.32
2026–2027	2.60	37.39	34.78	19,613.16	1.33
2027–2028	2.61	37.39	34.78	19,613.16	1.33
2028–2029	2.58	37.39	34.81	19,613.16	1.31
2029–2030	2.50	37.39	34.89	19,613.16	1.27
2030–2031	2.59	37.39	34.80	19,613.16	1.32
2031–2032	2.59	37.39	34.79	19,613.16	1.32
2032–2033	2.60	37.39	34.79	19,613.16	1.33
2033–2034	2.61	37.39	34.78	19,613.16	1.33
2034–2035	2.73	37.39	34.66	19,613.16	1.39
2035–2036	2.74	37.39	34.64	19,613.16	1.40
2036–2037	2.73	37.39	34.65	19,613.16	1.39
2037–2038	2.75	37.39	34.63	19,613.16	1.40
2038–2039	2.76	37.39	34.63	19,613.16	1.41
2039–2040	2.77	37.39	34.62	19,613.16	1.41
2040–2041	2.77	37.39	34.61	19,613.16	1.41
2041–2042	2.77	37.39	34.61	19,613.16	1.41
2042–2043	2.78	37.39	34.60	19,613.16	1.42
2043–2044	2.75	37.39	34.64	19,613.16	1.40
2044–2045	2.75	37.39	34.64	19,613.16	1.40
2045–2046	2.76	37.39	34.63	19,613.16	1.41
2046–2047	2.76	37.39	34.63	19,613.16	1.40
2047–2048	2.70	37.39	34.69	19,613.16	1.38
2048–2049	2.73	37.39	34.65	19,613.16	1.39
2049–2050	2.74	37.39	34.64	19,613.16	1.40
2050–2051	2.75	37.39	34.64	19,613.16	1.40

.

4.4. Calculation of Rabi Season Irrigation Water Demand

The monthly irrigation water demand throughout the rabi season was computed and is displayed in

Table 9. Gap between future average irrigation water demand and existing average irrigation water supply on a monthly basis for the rabi season.

Months	Irrigation Water Demand at HR (Mm3)	Irrigation Supply at HR (Mm3)	Difference (mm3)
December	0.38	0.00	−0.38
January	0.57	0.03	−0.55
February	0.57	0.72	0.15
March	0.72	0.81	0.09
April	0.60	0.90	0.30
May	0.32	0.48	0.16
Total	3.16	2.93	−0.23

. The maximum water demand for irrigation (0.72 Mm³) was found to occur in March, followed by April (0.60 Mm³) and January (0.57 Mm³). The month of May had the lowest demand for irrigation water (0.32 Mm³). As most of the crops, except sugarcane and turmeric, were planted prior to May, the lowest irrigation water demand was observed in May.

4.5. Comparison of Average Existing Irrigation Water Supply with Future Water Demand for Crops Throughout the Rabi Season

It is obvious from Table 9 that throughout the rabi season, the demand in two months (December and January) is greater than the monthly supply, except in four months (February to May). There is little variation in crop water demand and irrigation supply during these four months. The decadal average difference is −0.23 Mm³. Therefore, in addition to surface water, groundwater should be tapped as an additional irrigation water source to fulfill the crop water demands. There was a gap ranging from −0.55 to 0.30 Mm³ between the irrigation water delivered and mean monthly rabi irrigation water demand. A similar outcome was observed, i.e., during the dry season more irrigation water was needed than could be obtained from the canal using the current continuous canal delivery schedule [17,32]. Even though the monthly average for the irrigation water supply is 2.93 Mm³, most of the years had no irrigation water supply, so the rabi season irrigation water demand mostly depends on groundwater. The gap between future irrigation water demand and average existing irrigation water supply during the rabi season over thirty years is presented in

Table 10. Gap between future irrigation water demand and average existing irrigation water supply for the rabi season.

Year	Irrigation Water Demand at HR (Mm3)	10 Years Avg. Irrigation Supply at HR (Mm3)	Difference (Mm3)	Area × Factor	Water Table Fall (m)
2021–2022	2.87	2.93	0.05	19,613.08	1.46
2022–2023	3.11	2.93	−0.19	19,613.08	1.59
2023–2024	3.11	2.93	−0.19	19,613.08	1.59
2024–2025	3.11	2.93	−0.18	19,613.08	1.59
2025–2026	3.10	2.93	−0.18	19,613.08	1.58
2026–2027	3.11	2.93	−0.19	19,613.08	1.59
2027–2028	3.18	2.93	−0.25	19,613.08	1.62
2028–2029	3.18	2.93	−0.25	19,613.08	1.62
2029–2030	3.16	2.93	−0.24	19,613.08	1.61
2030–2031	3.18	2.93	−0.26	19,613.08	1.62
2031–2032	3.19	2.93	−0.26	19,613.08	1.62
2032–2033	3.17	2.93	−0.25	19,613.08	1.62
2033–2034	3.19	2.93	−0.27	19,613.08	1.63
2034–2035	3.18	2.93	−0.25	19,613.08	1.62
2035–2036	3.17	2.93	−0.25	19,613.08	1.62
2036–2037	3.18	2.93	−0.26	19,613.08	1.62
2037–2038	3.19	2.93	−0.27	19,613.08	1.63
2038–2039	3.18	2.93	−0.25	19,613.08	1.62
2039–2040	3.19	2.93	−0.27	19,613.08	1.63
2040–2041	3.20	2.93	−0.27	19,613.08	1.63
2041–2042	3.20	2.93	−0.28	19,613.08	1.63
2042–2043	3.20	2.93	−0.28	19,613.08	1.63
2043–2044	3.21	2.93	−0.28	19,613.08	1.63
2044–2045	3.21	2.93	−0.28	19,613.08	1.64
2045–2046	3.16	2.93	−0.23	19,613.08	1.61
2046–2047	3.17	2.93	−0.24	19,613.08	1.62
2047–2048	3.18	2.93	−0.25	19,613.08	1.62
2048–2049	3.15	2.93	−0.22	19,613.08	1.61
2049–2050	3.15	2.93	−0.22	19,613.08	1.61
2050–2051	3.16	2.93	−0.23	19,613.08	1.61

. The highest and the lowest irrigation water demand in the rabi season were predicted to be 3.20 (2044–2045) and 2.87 Mm³ (2021–2022), respectively, and the groundwater table fluctuation ranged from 1.46 to 1.64 m.

Table 10 shows that there is a small gap between future irrigation water demand and average existing irrigation water supply for the next 30 years during the rabi season due to the use of the optimal cropping pattern, which leads to higher water productivity [32,33]. For the (Shared Socioeconomic Pathways-1) SSP1-4.5 scenario, a decrease in irrigation water supply is anticipated (−26.8%), primarily due to a decrease in groundwater supplies; however, this is thought to be restricted to SSP1’s natural aquifer recharge [34]. At nearly every research site, surface water irrigation supply contributes more than groundwater during both the wheat and rice phases, with the exception of Haryana (rabi season) and Terai region of Nepal (kharif season), where groundwater supply predominates (up to 70%) [35]. The shortfall in rabi irrigation water demand could be fulfilled by groundwater sources, resulting in the declination of the groundwater table. The results indicated that, in the Bhadra command area, crop water requirement (CWR) increased during the kharif season under both SSP 245 and 585. However, the monthly irrigation water requirement (IWR) for the kharif season experienced a significant decrease, except in June. In the Tungabhadra command area, CWR showcased a decreasing trend, while monthly IWR increased for both seasons in future periods [36]. The results enhanced the understanding of water demand dynamics in agricultural areas, assisting policymakers and stakeholders in devising effective strategies to address climate change impacts on agriculture and encourage sustainable practices.

The uncertainty in the climate projections will affect future crop water demands and irrigation demands. Estimations of crop water requirements for the command area in the future period are necessary to learn the effect of climate change on individual crops [36].

Implications

The study highlights the urgent need to transition from a supply-based irrigation system to a future demand-driven model in the Phulnakhara canal command area. The current system’s efficiencies, under climate change scenario RCP 4.5 specifically, necessitate reforms in water allocation practices. To optimize conjunctive water use, it is recommended to prioritize high-efficiency crops in the tail regions of the canal command area, which have high unmet irrigation demands.

Further, implementing groundwater recharge strategies through managed aquifer recharge (MAR) and rainwater harvesting will help alleviate overreliance on groundwater. These findings should be integrated into regional and national water policies, especially the Water Apportionment Accord, to address regional disparities in water distribution.

5. Discussion

Climate projections from GCMs, considering various climate scenarios, have been utilized in several studies to determine the future irrigation demands of a command area [37,38]. There is a mismatch between demand and supply at the command area level [36,39]. The observed difference between future irrigation water demand and average existing water supply during kharif is much greater. However, the highest irrigation demand is primarily due to the critical growth period of paddy, other vegetables, and ginger in October. A significant amount of water is lost to seepage and evaporation before reaching crops, particularly from May to September, when many water-guzzling crops are cultivated [40]. The amount of water required for irrigation is found to be relatively low in August and June due to the heavy rainfall in these two months. As the future irrigation water demand estimate is based on the optimal cropping pattern, the irrigation water demand is marginally lower for future kharif periods than the existing 10-year average supply [29,33]. Due to the problematic tail reach of the canal command area and the high conveyance cost of water to farmers’ fields, farmers usually irrigate their crops using groundwater, thereby causing a fall in the water table [29,33]. Despite canal irrigation, the use of groundwater extraction to meet crop demands has led to a declining water table. The results indicate that the supply–demand gap increased due to the rising temperature and reduction in rainfall [40].

Surprisingly, during the rabi season, there was marginally less difference in crop water demand and irrigation supply during February to May in the future years under consideration. However, in the remaining two months, groundwater should be tapped as an additional irrigation water source to fulfill the crop water demands. The results were corroborated by the observation that, during the dry season, more irrigation water was needed than could be obtained from the canal using the current continuous canal delivery schedule [17,33]. Following the inclusion of the optimal cropping pattern obtained from the model, there was little gap between future irrigation water demand and average existing irrigation water supply for the next 30 years during the rabi season. Hence, estimating the crop water demands and irrigation water demands under climate change scenarios is essential for formulating the future policies of the Phulnakhara distributary in the main Puri canal. There has been limited research analyzing the impact of climate change on the crop water demands of the Phulnakhara canal command area.

The canal-lining scenario for improving conveyance efficiency was analyzed by [41,42]. The scenario analysis indicated that high-water-requiring crops, i.e., sugarcane must be replaced with crops that consume less water to reduce demand reduction, which will, in turn, save water [43,44,45]. A combination of alternating cropping patterns and irrigation system improvement is necessary and will be more effective in reducing irrigation water demand [46,47]. Lining canals and applying a sprinkler irrigation system could maximize system reliability by up to 17% and 25%, respectively [42]. Future climate change is expected to increase water shortages. For climate change scenarios, water shortage differences primarily arise when the water use rate is highest. Climate change has a strong effect on water use, but it comparatively weak effects on irrigation water supply and availability [47]. Multiple studies have predicted the impact of climate change on irrigation water demand or possible climate change adaptation pathways [48]. Under climate change scenarios, the results clearly show that unmet demand will increase in the future as compared to the reference scenario [49]. The results also show that the unmet water demand is higher under the climate change scenario with RCP 4.5 as compared to the climate change scenario with RCP 8.5 [50]. Demand-site water management approaches, i.e., a variable cropping structure and improved irrigation systems, will be effective in reducing adverse climate change impacts [47].

The present research was undertaken considering the RCP 4.5 scenario, and found that a decrease in the irrigation water supply is anticipated (−26.8%), primarily due to a decrease in groundwater supplies, which is thought to be restricted to SSP1’s natural aquifer recharge [34]. In almost every research site, surface water irrigation supply contributes more than groundwater during both the wheat and rice phases, with the exception of Haryana (rabi season) and the Terai region of Nepal (kharif season), where groundwater supply predominates (up to 70%) [35]. The findings suggest that climate change will have a notable impact on irrigation water demand, which is in line with previous studies [36]. The study specifically focuses on the command area, emphasizing the relevance of the aforementioned considerations, but the optimal cropping pattern and soil texture are assumed to be constant for future periods, which can be addressed in future studies. Overall, the results provide valuable insights for the command area development authority, which can facilitate sustainable development by optimizing cropping patterns and reservoir operation policies to enhance irrigation efficiency in response to changing climatic conditions.

5.1. Study Limitations

• The study relies on Global Circulation Model (GFDL–Global Coupled Model-CM3) for future climate projections, which may create uncertainties due to specific model assumptions.
• The canal water supply data used for comparison is limited to a particular historic period (2011–2012 to 2020–2021), which may not fully capture long-term trends in water supply.
• Socio-economic factors, such as changes in population growth and land use patterns, are not included in the current projections, potentially underestimating future water demand.
• The analysis focuses on the RCP 4.5 scenario, excluding the lower-emission pathways presented in RCP 2.5 and higher-emission pathways presented in RCP 8.5, and could offer an optimistic outlook.

Collectively, the above findings underscore the necessity of implementing various land and water management interventions, such as special automated canal gate closure systems with regard to the irrigation water supply, to prevent waterlogging, and the use of a micro-irrigation system in the canal command area. The growth and expansion of agriculture underscore the need for an integrated means of water resources management (conjunctive use of surface water and groundwater) that considers the increase in water productivity and food production while conserving the ecosystem.

5.2. Future Directions

Future irrigation water demand can be predicted for different scenarios by using a micro-irrigation system instead of a canal irrigation system, considering low-duty crops instead of water-guzzling crops, etc.

6. Conclusions

The average result over a decade shows that there is a significant discrepancy between supply and demand because there is an inconsistency between the supply of canal irrigation water and the demand for agricultural water during the kharif season in future years. Thus, through efforts such as accurate evaluations of crop coverage and crop water demand, and effective flow delivery through enhanced canal operation, the supply and demand for each year should be balanced. October is the critical month, occurring in the kharif season, where a significant discrepancy between supply and demand was observed. Therefore, this season needs special arrangements, such as an automated canal gate closure system, with regard to the supply of water for irrigation, to prevent waterlogging in the canal command area. Cropping intensity and productivity are low due to the canal’s inconsistent operation and the huge gap between the irrigation supply and demand during the rabi season. Based on the findings of the current study and the scenario analysis, different strategies are proposed for the efficient and effective utilization of the present water resources. The RCP 4.5 scenario, including improved irrigation systems and the reduction and replacement of high-water-guzzling crops with less water-consuming crops, should be practically implemented. Canal should be operated at full supply levels, and proper maintenance should be enforced. Rainwater should be harvested, particularly in the monsoon season, by developing small storage reservoirs for use in dry seasons. Based on the future climate change scenario, traditional alternative water regulation policies should be revised and reoriented based on crop types and the optimal area covered, as well as on-farm water demand for efficient water allocation. It is consequently advised to use the groundwater resources, which are abundant in the research area, to provide the necessary demand. In order to satisfy the canal command area’s crop water demands, surface water and groundwater must be used in concert. Optimizing the timing of canal deliveries could help somewhat narrow the gap between supply and demand. The most important findings of this study are provided below:

• It is concluded that by adopting the future climate projections RCP 4.5 scenario, a consistent increasing trend in temperature until 2050–2051 and a rising trend in rainfall until 2034 can be observed for the canal command area.
• Future monthly irrigation demand for the kharif season in the Phulnakhara canal command area indicates a substantial reduction for July, August, and September, in line with the increase in monsoon precipitation, which could effectively satisfy the water demand in the command area. However, the projected rise in temperature in the future period increases irrigation demand during January to April (rabi season).
• The study addresses the uncertainty in future irrigation demand stemming from climate variables. It employs one of the best-performing GCMs, an optimized cropping pattern, and the Hargreaves method, a widely accepted method with minimal involvement of climate data, which predicted low water table declination and high reservoir releases in future periods.

The outcome of the study provides a foundation for adaptation strategies, including optimal cropping patterns, ways of managing water demand, and water-harvesting structures, thereby optimizing future cropping patterns and irrigation releases from the main canal based on future water availability for various climate change scenarios in the Phulnakhara canal command area.