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Reconciling the impacts of extreme rainfall events and extended drought on pasture and livestock production: a new method for generating synthetic climate sequences


Harrison, M and Cullen, B and Rawnsley, R, Reconciling the impacts of extreme rainfall events and extended drought on pasture and livestock production: a new method for generating synthetic climate sequences, Livestock, Climate Change and Food Security 2014, 19-20 May 2014, Madrid, Spain (2014) [Conference Extract]

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Past work examining the e ffects of climate change on agricultural productivity typically uses downscaled weather forecasts generated from global circulation models. Use of prescribed emission scenarios and time horizons in such approaches predefines the number of extreme climatic events (ECEs) that occur in forecasts of future climate. Further, forecasts containing both gradual climate change and more frequent ECEs make it difficult to partition and identify the impact of each factor on farm production.
Here we outline a new approach for generating synthetic sequences of weather containing extreme rainfall events and extended drought. Our approach preserves historical climate characteristics and does not include e ffects of gradual climate change, allowing the sensitivity of pasture and livestock production to ECEs to be determined. The method randomly selects a defined proportion of rainfall events based on their magnitude and scales each event accordingly. A key advantage of this framework is retention of dependencies in daily weather variables, including the coupling between minimum and maximum daily temperatures, and the duration of contiguous dry days.
We modified a 20-year sequence of historical weather measured at a site in Tasmania, Australia, such that the average maximum continuous duration of dry days per annum increased by 40%, the average maximum daily precipitation intensity increased by 40-50%, and the average annual rainfall decreased by 15% (in line with climate forecasts for 2070-99). We used the synthetic weather sequence in a dairy farming systems model and found that runoff increased by up to 5 mm/month, yet soil water draining from the base of the profile decreased by as much as 36 mm/month. Together these factors reduced peak annual pasture growth rates and caused earlier declines in plant growth rates as spring progressed into summer. This lowered biomass production such that pasture intake per animal decreased by 11%. To maintain the same level of historical milk production, grain and hay feeding requirements increased by 11-14%, while the range in milk production increased by 19%.
Our new approach for constructing synthetic weather sequences will facilitate further analyses of the eff ects of extended drought and reduced rainfall on farm production. In future this methodology will be extended to temperature extrema, allowing examination of the potential impacts of more heat waves and cold snaps. The overall eff ects of more severe and frequent ECEs on biophysical production on will ultimately be integrated within a wider framework containing economic, social and cultural aspects of dairy businesses.

Item Details

Item Type:Conference Extract
Keywords:climate change, dairy, mitigation, adaptation, risk, variability, extreme event
Research Division:Agricultural, Veterinary and Food Sciences
Research Group:Agriculture, land and farm management
Research Field:Agricultural systems analysis and modelling
Objective Division:Environmental Policy, Climate Change and Natural Hazards
Objective Group:Understanding climate change
Objective Field:Climate variability (excl. social impacts)
UTAS Author:Harrison, M (Associate Professor Matthew Harrison)
UTAS Author:Rawnsley, R (Dr Richard Rawnsley)
ID Code:90607
Year Published:2014
Deposited By:Tasmanian Institute of Agriculture
Deposited On:2014-04-14
Last Modified:2014-04-14
Downloads:8 View Download Statistics

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