CNAS

Australia

Holger R. Maier, Graeme C. Dandy, Fiona L. Paton, School of Civil, Environmental and Mining Engineering, The University of Adelaide

Jeff Connor, CSIRO Land and Water

“Diversification of Adelaide’s water supply in response to drought”

Adelaide is the capital of South Australia and has a population of approximately 1.3 million. In wet years, Adelaide obtains most if its water supply from the nearby catchments in the Adelaide hills. However, in dry years, about 90% of Adelaide’s water supply needs are met by water that is pumped from the River Murray. Severe drought in the Murray Darling Basin over the past few years has meant that the security of Adelaide’s water supply has been threatened. This chapter examines the impact on costs and greenhouse gas emissions of the response to this threat, which consist of the diversification of Adelaide’s water supply sources to include desalination, rainwater and recycled stormwater and wastewater.

California

James E. Ayars, USDA-ARS, San Joaquin Valley Agricultural Sciences Center

"Adapting irrigated agriculture to drought in the San Joaquin Valley of California"

Webster’s dictionary defines drought as a continuous state of dryness but does not define a cause for that dryness, just the existence. Thus, even in times of plentiful water supply a drought condition could exist in irrigated agriculture due to demands from municipal, industrial and environmental interests. The challenge for agriculture is to improve water productivity to compensate for any potential losses to competing demands. This manuscript will discuss options for improved water productivity including changing irrigation systems, improving water and fertilizer use, and new irrigation water management strategies to include regulated deficit irrigation (RDI), partial rootzone drying (PRD). Alternative water management strategies will be discussed including defining production goals based on the available water supply, integrated water management of irrigation and drainage systems, cropping alternatives, and physical management of crops e.g. pruning and thinning.

South Africa

Hannes Rautenbach and John Annandale, Faculty of Natural and Agricultural Sciences, University of Pretoria

"Drought frequencies and its influence on agricultural practices in South Africa"

Apart from being located in the dry subtropics of the world, South Africa’s climate and water availability is affected by local as well as remote (eg. El Niño) land and ocean surface changes. For example, changes in surface radiation between the warmer southern African continent and colder surrounding oceans might lead to the development of synoptic scale surface troughs (lower pressures) over the warmer continent during austral summer months. These troughs are of great importance since their cyclonic rotation might allow for moisture advection from wetter equatorial African regions towards the eastern parts of South Africa where most of the summer rain falls, so that rainfall increases zonally in January from less than 10mm over the dry west to just more than 200mm over the east. The major maize production areas of South Africa are located in the austral summer rainfall region. This study will explore drought frequencies over the austral summer rainfall region (on an intra as well as inter-annual time scale), will look at the contribution of rainfall to water availability, and will provide information about the impact of these drought frequencies on agricultural practices in the region under investigation.

Spain

E. Playán , N. Zapata, and J. Cavero, Department of Soil and Water, Aula Dei Experimental Station, CSICS

S. Lecina , D. Isidoro, and R. Aragüés, Soil and Irrigation Department, Agrifood Research and Technology Centre of Aragon, CITA

"Living with drought in the irrigated agriculture of the Ebro basin (Spain): structural and water management actions"

This chapter discusses a set of technological actions aiming at living with drought in the irrigated agriculture of the Ebro basin in Spain. The basin faces recurrent drought episodes which have led water authorities and farmers to take actions on the structural and water management aspects of water conservation. Structural works have implied large irrigation modernization plans in about half of the 840.000 ha which are currently irrigated. Modernization typically implies the construction of collective, remotely-controlled, pressurized irrigation networks and the installation of on-farm sprinkler/drip irrigation systems. The impacts of these modernization projects on the Ebro basin hydrology, both in terms of water quantity and quality, and on the economy and productivity of irrigated agriculture are discussed. In parallel, actions have been promoted to improve water management, mostly at the irrigation district level. The co-operative design, elaboration and dissemination of a database software supporting daily water management operations in irrigation districts is presented, and the prospects for water conservation are analyzed. Finally, an action plan dealing with improvements on structures and water management capacities is presented. This new action comprises automated irrigation scheduling and operation, and is based on a combination of remotely controlled networks, district water management and meteorological databases and irrigation engineering tools. The proposed action has already undergone significant research and could result in the generalization of scientific irrigation scheduling and in the complete automation of irrigation operation. Technology can support farmers in their efforts to adapt to drought conditions and still obtain sustainable profits.