Grazing indices for the Central Karoo

Year: 2019
Working paper number: 442
Author: Beatrice Conradie,Stefan Theron
Unit: CSSR

This paper presents Du Toit’s Grazing Indices for eight Central Karoo locations. The Du Toit Index is a twelve-month moving total of rainfall, computed from monthly rainfall statistics, which assumes that the benefit of a specific rainfall event depreciates linearly over twelve months. Rainfall varies by a factor of four in this dataset, from 112 ± 52 mm per year at Laingsburg village to 410 ± 128 mm per year in the Sneeuberg. Six of the eight indices are based on more than 90 years’ observations and the shortest series covers almost 60 years. The depth and duration of each drought is described relative to expectations at each location. A drought begins when the grazing index falls below the 10th percentile of observations on record and ends when it exceeds the 50th percentile. Sometimes this happens within three months and other times recovery can take years. By September 2019 the drought was ongoing at all but one site across the region and, at all but two sites, the current drought has reached the deepest level of record at some point during the last three years. Producers can use this index to predict downside risk three to six months ahead and it can inform policy makers’ budgeting process. The analysis also raises bigger questions about the opportunity cost of drought relief and the appropriate response to disaster relief in a time of climate change.

Publication file: ConradieTheron.pdf