Supplemental irrigation potential and impact on downstream flow of Karkheh River basin in Iran

Abstract

Abstract. Supplemental irrigation of rainfed winter crops improves and stabilises crop yield and water productivity. Although yield increases by supplemental irrigation are well established at the field level, its potential extent and impact on water resources at the basin level are less researched. This work presents a Geographic Information Systems (GIS)-based methodology for identifying areas that are potentially suitable for supplemental irrigation and a computer routine for allocating streamflow for supplemental irrigation in different sub-basins. A case study is presented for the 42 908 km 2 upper Karkheh River basin (KRB) in Iran, which has 15 840 km 2 of rainfed crop areas. Rainfed crop areas within 1 km from the streams, with slope classes 0-5, 0-8, 0-12, and 0-20 %, were assumed to be suitable for supplemental irrigation. Four streamflow conditions (normal, normal with environmental flow requirements, drought and drought with environmental flow) were considered for the allocation of water resources. Thirty-seven percent (5801 km 2 ) of the rainfed croplands had slopes less than 5 %; 61 % (3559 km 2 ) of this land was suitable for supplemental irrigation, but only 22 % (1278 km 2 ) could be served with irrigation in both autumn (75 mm) and spring (100 mm), under normal flow conditions. If irrigation would be allocated to all suitable land with slopes up to 20 %, 2057 km 2 could be irrigated. This would reduce the average annual outflow of the upper KRB by 9 %. If environmental flow requirements are considered, a maximum (0-20 % slopes) of 1444 km 2 could receive supplemental irrigation. Under drought conditions a maximum of 1013 km 2 could be irrigated, while the outflow would again be reduced by 9 %. Thus, the withdrawal of streamflow for supplemental irrigation has relatively little effect on the outflow of the upper KRB. However, if the main policy goal would be to improve rainfed areas throughout the upper KRB, options for storing surface water need to be developed.

Conjunctive use of green and blue water resources in agriculture: Methodology and application for supplemental irrigation*

“…Roughly this potential amounts to in (2008a) for Syria, suggesting that allocating the same amount of water used for fully irrigated summer cotton crop to a partially irrigated winter wheat crop would result in more than doubling the area under irrigation. The present study confirms the findings of Hessari et al (2016), who used lumped modelling to find suitable SI areas in the whole of the upper KRB and to predict the expected consequences of water flowing downstream to Karkheh dam. The authors reported that under normal flow conditions, about 2060 km 2 , which represents 13% of the rainfed crop areas and 28% of suitable areas, could be provided with SI in autumn and spring.…”

“…The present study confirms the findings of Hessari et al . (2016), who used lumped modelling to find suitable SI areas in the whole of the upper KRB and to predict the expected consequences of water flowing downstream to Karkheh dam. The authors reported that under normal flow conditions, about 2060 km 2 , which represents 13% of the rainfed crop areas and 28% of suitable areas, could be provided with SI in autumn and spring.…”

“…However, spatial water allocation with geographic information system (GIS) tools is widely used for several applications. Lumped, node‐to‐node, semi‐distributed, and fully distributed water allocation algorithms were utilized to optimize irrigation water usage from an irrigation scheme to large basins (De Pauw et al ., 2008b; Ashrfa Vaghefi et al ., 2014; Hessari et al ., 2016). Limited work was found regarding water allocation under SI in dry‐farming systems.…”

Shatt al Arab River system under escalating pressure: a preliminary exploration of the issues and options for mitigation

“…Its discharge flows into the transboundary Hawizeh marshes that straddle the Iraqi and Iranian border (Masih et al 2011, Hessari et al 2012). The total annual renewable water resource (both surface and groundwater) is estimated at 8.6 × 10 9 m 3 /yr of which 2.5 × 10 9 m 3 /yr was the total consumptive use in 1993-1994.…”

Detecting Land use Changes Affected by Human Activities using Remote Sensing (Case Study: Karkheh River Basin)

“…Improvement of water productivity is an upside preference in agricultural strategies of Iran (Asmala, 2012). To increase in amount of water productivity and crop in the upper plains of the basin supplemental irrigation has been recommended (Hessari et al, 2012).…”