CNAS

Australia

Ian Overton, CSIRO

"The Murray-Darling Basin: An ecosystem under threat in Australia"

The Murray-Darling Basin is one of Australia’s largest river Basins, and contains highly valued water-dependent ecosystems, including 10 Ramsar listed wetlands. Through the impact of drought and overallocation, 69% of the basin’s water is abstracted for irrigation and human consumption, these ecosystems are now severely degraded. Future climate scenarios suggest a drier and more variable climate with continued and intensified drought periods. Future water sharing policies need to increase the amount of environmental water, as well as its security, to improve the condition and resilience of the ecosystem. This chapter outlines the challenges involved in managing ecosystem adaption to a drier climate while maintaining key ecosystem assets.

California

G. Darrel Jenerette, University of California Riverside, Department of Botany and Plant Sciences

“Ecosystem resiliance and regimes shifts in response to precipitation variability: Multiple responses to multiple timescales”

Ecosystems environments respond to precipitation variability through multiple mechanisms. Physiology, phenology, disturbance regimes, and community assemblages processes are each sensitive to water availability and can have consequences for ecosystem change at multiple scales. Droughts are a severe form of precipitation variability, but how ecosystems respond will depend on the history of precipitation variability and current configuration. A critical challenge for ecosystem scientists is generating a better understanding of when and how ecosystems are resilient or respond with regime shifts to precipitation variability. This chapter will describe the current state of knowledge in ecosystem sensitivity to precipitation variability with an emphasis on how droughts, both as extreme events and chronic conditions, may change ecosystems. Examples will be collected primarily from the southwestern United States and in particular California. Policy implications of likely ecosystem responses will be further explored.

Mexico

Irene Pisanty, Cristina Pérez and Gabriel Gálvez, Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México

"Agriculture, water mismanagement and ecosystem transformations in the Cuatrociénegas Valley in the Chihuahuan Desert, Mexico"

Water overexploitation affects the Churince System, one of the wetlands of the Cuatrociénegas Valley in the Chihuahuan Desert. Presumably associated with neighbouring agricultural developments, water levels are diminishing and the appearance of soil subsidences, through which water is lost, has accelerated. We registered the formation of subsidences, their size, depth, level of water, and the colonizing pattern of the plants that occupy them, and analysed the population dynamics of one of the main colonizing species. We conclude that subsidences are indicators of environmental health that should be used as an early warning system to protect a region where mismanagement is affecting ecosystem integrity.

South Africa

Rashid Hassan, CEEPA, University of Pretoria

"The potential of economic instruments in managing hydrological drought to achieve national water policy objectives and promote adaptive capacity among water users in South Africa"

The current strategy for managing hydrological drought in South Africa is based on low flow water allocation regimes. This study aims to evaluate the efficacy and appropriateness of current drought management strategies for achieving the principal objectives of the national water policy which promotes social equity, ecological protection and economic efficiency. In pursuit of this, the chapter also intends to explore the potential of economic instruments in providing proper incentive measures to enhance the adaptive capacity of water users in response to drought and contribute to achieving strategic national water policy objectives.

Spain

Carles Ibáñez and Nuno Caiola, IRTA, Aquatic Ecosystems Program

“Impacts of water scarcity and drought on Iberian aquatic ecosystems”

Most of the Iberian Peninsula (Spain and Portugal) is under Mediterranean climate and undergoes cyclical droughts in natural conditions. Moreover, this region is expected to be one of the most impacted ones by climate change, which will likely exacerbate the frequency and span of droughts. The historical development of irrigation and the recent economic development put additional pressure on the scarce fresh water resources. Consequently, most of the rivers, lakes and estuaries are impacted by the reduction and regularization of the flow regime. The main responses of Iberian aquatic ecosystems to increased water stress are reported to be: changes in biotic community structure, changes in habitat availability, alteration of ecosystem metabolism, increase of eurytolerant and invasive species, and reduced resilience against global change impacts. One of the main measures to be implemented for mitigating the effects of water scarcity in Mediterranean aquatic ecosystems is the establishment of a pulsing environmental flow regime. Future research should focus on quantifying the ecological effects of water scarcity and the role of environmental flows in maintaining ecosystem structure and function.