Bias corrections of long-term (1973-2004) daily precipitation data over the northern regions

A consistent daily bias correction procedure was applied at 4802 stations over high latitude regions ( North of 45 degrees N) to quantify the precipitation gauge measurement biases of wind- induced undercatch, wetting losses, and trace amount of precipitation for the last 30 years. These corrections have increased the gauge- measured monthly precipitation significantly by up to 22 mm for winter months, and slightly by about 5 mm during summer season. Relatively, the correction factors ( CF) are small in summer ( 10%), and very large in winter ( 80 - 120%) because of the increased effect of wind on gauge undercatch of snowfall. The CFs also vary over space particularly in snowfall season. Significant CF differences were found across the USA/ Canada borders mainly due to differences in catch efficiency between the national gauges. Bias corrections generally enhance monthly precipitation trends by 5 - 20%. These results point to a need to review our current understanding of the Arctic fresh water budget and its change.