Drought is a recurrent feature of climate involving a deficiency of precipitation over an extended period of time, resulting in a water shortage for activities, communities or aquatic ecosystems. In British Columbia, drought may be caused by combinations of insufficient snow accumulation, hot and dry weather or a delay in rainfall.
Drought can be defined as meteorological, hydrological, agricultural or socioeconomic, each of which implies different impacts.
Hydrological Drought (Primary basis for determining Provincial Drought Levels)
Hydrological drought is associated with the effect of low precipitation on water levels in rivers, reservoirs, lakes and aquifers. Hydrological droughts usually are noticed some time after meteorological drought.
Agricultural drought occurs when there is not enough water available for a particular crop to grow or livestock to thrive at a particular time. This drought does not depend only on the amount of precipitation, but also on the correct use of water. Agricultural drought is typically seen after meteorological drought and before hydrological drought.
Meteorological drought is generally defined by comparing the rainfall in a particular place and at a particular time with the average rainfall for that place. Meteorological drought leads to a depletion of soil moisture and this almost always has an impact on crop production. When drought is defined in this way, only reductions in rainfall are considered. The impacts of the lack of water on water reservoirs, human needs or on agriculture are not taken into account.
Socio-economic drought occurs when the demand for economic goods exceeds their supply as a result of a weather-related shortfall in water supply.
The province of BC uses four core indicators and additional supplemental indicators to establish:
if there is a drought or a possibility of drought
what the drought level is at a given point in time.
The province measures the following four core indicators to establish whether there is a drought:
Basin Snow Indices
Seasonal Volume Runoff Forecasts
30 Day Percent of Average Precipitation
7-Day Average Streamflow
The drought level is linked to a threshold established for each of the core indicators.
In addition, the following supplemental indicators also help assess the situation.