MODELING WATER DEMAND IN THE OKANAGAN BASIN, BRITISH COLUMBIA

The Okanagan Basin is a small semi-arid watershed in which 90% of the available water has been allocated and agriculture uses 70% of the water that is currently licensed. Competing demands among ecosystem requirements, agriculture, recreation and urban growth has resulted in the Okanagan Water Supply Demand Project which is developing a basin water balance. We will report on the development and findings of a group of models designed to estimate the agricultural, outdoor domestic and institutional demand components of this regional study. The Okanagan Irrigation Water Demand Model is a GIS based model which estimates water demand based on crop type, seasonal crop development and spatial distribution. Multiple data layers which characterise topography, surface and subsurface hydrology, crop distribution, irrigation management practice, soils and a range of geographic and political boundaries inform the model. Modeling water supply and demand requires climate data inputs that reflect the complex terrain of the area. The Okanagan Climate Data Model generates fine scaled climate surfaces providing daily temperature and precipitation values on a 500 x 500m for the years 1960-2005. Current and future climate data sets have also been downscaled from GCM output (12 scenarios) from 1960-2100. The Okanagan Climate Data Model provides calculations of Penman Monteith reference ET and a range of agro-climatic indices for each climate grid cell to drive the Okanagan Irrigation Water Demand Model. Estimates of water demand under current and future climates, and scenarios of changing crop profiles and irrigation management will be discussed.