The Agricultural Water Demand Model (AWDM) was developed for Metro Vancouver in 2013 in order to help understand current and future agricultural water demand and support BC’s commitment to reserve water for agricultural lands. The model uses a Geographic Information System (GIS) database that combines information on crop, irrigation system, soil texture and climate to estimate irrigation demand specifically for Metro Vancouver’s ALR .
Metro Vancouver’s ALR (above) comprises approximately 60, 000 ha of land where agriculture is the prioritized land use. Within the entirety of Metro Vancouver, land used for agriculture comprises 40, 000 ha; 30, 000 ha (75%) of which (including almost all of the irrigated area) is found within the ALR . The land use breakdown of Metro Vancouver’s ALR is summarized in the table below.
Description of AWDM Factors
Crop and Irrigation System: Land use information including crop and irrigation system was assembled through a combination of aerial photo review and land surveys conducted in 2010-2011 .
Soil: The Ministry of Environment’s Terrain and Soils Information System was used to assemble soil information. The Computer and Assisted Planning and Map Production application (CAPAMP) was used to access soil surveys for the Lower Mainland performed in the 1980s. The ability of soils to store and transmit water is dependent on a number of soil properties such as organic matter content, soil structure, soil texture, hydraulic conductivity etc . The model employs soil texture and the available water storage capacity and peak infiltration rate for each texture to estimate demand. Consequently, soil texture is the property used in this investigation as an indicator of how water is transmitted and stored within the soil .
Climate: The climate dataset was created from assembled climate station data in the Lower Mainland. Climate data from these stations was interpolated to create a 500m x 500m grid. Each cell employs daily min, max and mean temperature and precipitation, which are used by the model to calculate the reference evapotranspiration rate and a range of agro-climatic indices (Growing degree days, frost free days, temperature sum, effective precipitation, corn heat units, first frost date) .
The AWDM does not include the height of the water table in the calculations of water demand. Since high water tables would reduce irrigation demand, and Metro Vancouver comprises many low-lying regions with high water tables, the estimated water demand from the Model will be higher than what may actually be used .