Declining relative humidity in the Thompson River Valley near Kamloops, British Columbia, Canada: 1990-2012

Potential time trends in relative humidity (RH) were investigated for the Kamloops climate station in a semi-arid region of south-central British Columbia, Canada, between 1990 and 2012. Mean monthly 6 am and 3 pm RH at Kamloops achieve annual minima during the March to September period with substantially higher early morning RH compared to the mid-afternoon period. Significant temporal declines in RH throughout the year are evident ranging from 1.5 to 5.7%/decade. No significantly increasing temporal trends in RH were found. The findings indicate that a continuation of declining trends in RH for the study area may increase the quantity of dust and other atmospheric particulate generation from both natural and anthropogenic sources, possibly resulting in additional threats to local and regional air quality, thereby necessitating inclusion in air quality management planning and modeling efforts.