MODELING THE EFFECT OF REGIONAL AND LOCAL PRECIPITATION EVENTS ON GROUNDWATER RECHARGE

Water in the Okanagan Valley, British Columbia, is recognized as a limited resource that may become unsustainable within a few decades due to population expansion and climate change. The valley has an arid climate due to the rainshadow effect caused by the Coast Mountains (median precipitation is 280 mm/year). Groundwater recharge within the Okanagan Valley depends on many factors, including the infiltration rate, which itself, depends on the precipitation rate. The analysis and graphical representation of observed daily climate data variables (maximum, mean & minimum temperature; rain, snow & total precipitation) provides insight for understanding the dynamics of the climatology of the region, which has direct impacts on the hydrologic cycle. To investigate the controls on infiltration, and thus, recharge rates in the Okanagan, daily precipitation data at two meteorological stations are compared using a cross-plot, and classed into regional and local precipitation events. Local precipitation events can be regarded as being delivered from convective clouds, which have high precipitation rates, limited spatial and temporal scales (0.5 – 2 km, 5 – 100 minutes), and derive their source water from local evapotranspiration. Regional precipitation can be regarded as being from frontal precipitation climate systems, which have a lower precipitation rate, larger spatial and temporal scales (10 – 300 km, 0.5 – 5 days), and which derive their source water largely from the ocean. Daily classed precipitation data are used as model inputs for the 1D unsaturated recharge model, HELP, and the recharge response is calculated at the unsaturated/saturated interface. Regional precipitation events contribute significantly to recharge in comparison to local events. Statistical and graphical displays of climate variables are offered as a publicly distributed “climate.plot” package for the R statistical computing program. The package is capable of calculating and plotting detailed seasonal temperature and precipitation normals, as well as estimating seasonal precipitation intensities.