Assessment of water, energy and agricultural needs for sustainable development in the Sava River Basin

A new report co-authored by UNECE-JRC-KTH looking at the Sava River Basin shows that water management planning is needed in order to meet the long-term renewable energy targets.

The UNECE report calls for increased coordination and cooperation to ensure best management of the water-food-energy-ecosystems nexus in the Sava River Basin ©UNECE

The report, prepared within the framework of the UNECE Convention on the Protection and Use of Transboundary Watercourses and International Lakes, assesses the Water-Food-Energy-Ecosystems Nexus in the Sava River Basin – a large tributary river of the Danube, covering parts of Slovenia, Croatia, Bosnia-Herzegovina, Serbia and Montenegro.

The report and its recommendations are the result of a participatory assessment carried out in cooperation with the International Sava River Basin Commission. It concludes that, in order to meet the long-term renewable energy targets, the Sava countries rely heavily on the basin’s water resources. Key to achieving climate change mitigation targets in the region are hydropower investments in the Sava Basin, which are expected to account for 43% of carbon dioxide reductions in the riparian countries by 2030. Despite the importance of energy security for most of these countries, development planning for the energy sector is not necessarily connected with water management planning, which also has to ensure necessary water for agriculture and other water uses. This calls for increased coordination, information sharing and transboundary cooperation.

With the current energy sector outlook, the report cautions that the trade-off between hydropower development and agricultural expansion needs to be carefully managed. Significant increases in crop yields could be obtained by optimising irrigation, but this could have substantial effects on surface- and groundwater flow (especially in the lower Sava Basin during dry periods) and reduce water availability for hydropower generation on some of the tributaries.

The Sava nexus assessment also pinpointed various solutions to address these intersectoral challenges, including the flexible use and upgrading of infrastructure (in particular dams, irrigation and drainage systems and wastewater treatment plants), coordinating infrastructure investments (notably in hydropower and other renewable energy sources), and protecting natural infrastructure assets, including floodplains and wetlands.

JRC contribution

JRC scientists and experts of the KTH Royal Institute of Technology in Stockholm carried out a water resources modelling and crop modelling study in the Sava basin, simulating current and future climates, as well as current and future land use and socio-economic conditions. (See also the JRC technical report published in 2016.)

This study showed that more intense irrigated agriculture could increase crop yields considerably, but that available water resources are not sufficient. Also, a drastic increase in irrigation would negatively affect other sectors such as the energy sector (reduced cooling water availability, potentially less water for hydropower production), navigation (more frequent and lower low-flows), and the environment (breaches of environmental or minimum flow conditions).

Forested, urban and industrial areas to expand by 2050

With respect to most of the water resource indicators, the projected land use changes until 2050 balance each other out, and the net effect is only marginal. Land use projections for Slovenia until 2050 are for a substantial increase in forested area at the expense of arable land and semi-natural vegetation. Urban land use is expected to increase by roughly 22%, industrial land use by roughly 27%. For Croatia, forest areas are expected to increase substantially, with 50% of the country’s land surface projected to be forested by 2050. Areas of arable land and semi-natural vegetation are expected to decrease substantially. Industrial and urban land uses are expected to increase by 22% and 1% respectively.

Agricultural water demand to increase significantly

Effects on water resources would be more significant, with increased irrigation to increase crop yields, e.g. of maize. This would lead to an increase in water demand from 2 216 Mm3/year to 3 337 Mm3/year. Combining both increased irrigation and climate projections until 2100O, oerall water demand in the Sava basin would further increase to around 6 000 Mm3/year. The average simulated maize yield could almost double, increasing from 5.7 tonnes/ha under present conditions to 9.9 tonnes/ha under increased and optimum irrigation. These substantial increases in irrigation, which would lead to substantial crop yield increases as well, would lead to water scarcity in parts of the Sava basin. Also, there just is not enough water to irrigate all areas which are water-limited for crop growth.

Existing irrigation plans and irrigating the areas which were previously equipped for irrigation (according to the FAO) seems more feasible from a water resources perspective.

Soil water stress conditions, which could potentially reduce agricultural crop yields, particularly affect the lower parts of Bosnia-Herzegovina, Croatia and Serbia under current climate conditions. Climate impact simulations show an increase of soil water stress of 9% for 2030. For the end of the century, RCP4.5 (global warming scenarios of a 1.8˚C increase by 2100) shows a 1% increase, whereas RCP8.5 (global warming to increase by 3.7˚C by 2100) shows a 7% increase in soil water stress. This might indicate stronger needs for irrigation in the future to maintain current crop yields.

More floods likely due to climate change

Flood peaks are projected to remain unchanged as a consequence of projected land use changes until 2050 for the Sava basin. However, with climate change projections we do simulate an overall increase in the flood peaks with 13% for the 2011-2040 period and a 23% increase for the 2071-2100 period.

River low-flows are expected to decrease moderately for the 2011-2040 scenarios. For the end of the century (2071-2100), low-flow values are projected to moderately increase as compared to the control (1981-2010) climate. Excessive irrigation would result in a severe (50-60%) decrease of the low-flow discharges. Similar observations can be made for ecological flows.

Water supplies for energy production

Water availability for energy production (hydropower and cooling water for thermal and nuclear power stations) is projected to decrease by an average of 3.3% by 2030 under RCP4.5 (global warming scenarios of a 1.4˚C increase by 2065), whereas RCP8.5 (global warming to increase by 2.0˚C by 2065) would result in a 1.3% increase. End of the century simulations yield a 17.6% higher Q50 for RCP4.5 and 23.1% higher for RCP8.5. Excessive irrigation could affect the water availability for power production, especially for cooling thermal power stations. Hydropower reservoirs could be turned into multi-functional reservoirs, which would serve multiple purposes including downstream irrigation needs and flood control.

Groundwater supplies

Our climate impact simulations show a moderate decrease in groundwater resources for Slovenia and the higher parts of Croatia and Bosnia Herzegovina until 2030. For the end of the century runs we observe increases in groundwater resources. Increased irrigation practices would seriously reduce groundwater resources again. Also, if relatively more groundwater is used for irrigation replacing surface water, groundwater resources also decrease.