Climate variability refers to the deviation of climate statistics over a given period of time (for example a specific month, season or year) from the long-term climate statistics relating to that corresponding calendar period. It thus describes how the climate over a comparatively short period varies from long term climatic averages with direct consequences for water resource management. For example one direct result may be a change in availability of surface and groundwater resources. Individual events such as the El Niño or El Niña Southern Oscillation phenomena or volcanic activity can cause significant climate variation.
A critical variable for assessing trends in precipitation and evapotranspiration is the Coefficient of Variation (CV), which can be applied to monthly meteorological data.
Coefficient of Variation for the Climate Moisture Index (CMI CV) on a 0.5 X 0.5 degree global grid.
Source: GWSP Digital Water Atlas (2008). Map 65: Coefficient of Variation for Climate Moisture Index (V1.0). Available online at http://atlas.gwsp.org
( click to enlarge )
The CV is a statistical measure of the potential seasonal and interannual fluctuations in water availability for regions. Increased climate variability indicates larger year-to-year fluctuations, a higher CV and hence, less predictability in the climate.
CV is seen as a more accurate assessment for water availability than annual average precipitation / evapotranspiration, as it shows the natural year-to-year variability. Higher CV indicates a greater degree of precipitation on a year-to-year basis in a specific area (Schulze 2006).The variability of precipitation and evapotranspiration, both in time and in space across a region, directly influences the availability and variability of surface and groundwater resources.
For a range of CV values found in the Kunene River basin see Climate Variability in the basin.
