Significant climatic changes over the high latitudes in the 20^th century have caused changes in many atmospheric, oceanic, and terrestrial variables. While changes in surface air temperature and precipitation are most commonly addressed in the literature, changes in their derived variables (variables of economic, social and ecological interest based upon daily temperatures and precipitation) have received less attention. This presentation will shed light on some changes in a set of these derived variables over the past fifty years. Our analysis has been done using a subset of about 1500 stations north of 50°N from the recently created Global Daily Climatology Network archive. Time series of the following variables have been constructed and the observed changes during the past fifty years will be described at the symposium:

frequency of extremes in precipitation and temperature; frequency of thaws; heating degree days; growing season duration; sum of temperatures above/below a given threshold; days without frost; day-to-day temperature variability; precipitation type fraction; precipitation frequency; frequency of rain-on-snow events; and Keetch- Byram (Soil Moisture) Drought Index.

Specific applications of these derived variables are numerous, ranging from crop-yield modeling and energy distribution to forest fire and flood forecasting. Changes in these variables imply increases and decreases in risk. Whatever "implications" would be assigned to these observed changes, it is important to note that many of them have been significant enough to be noticed above the usual "weather" noise level during the past fifty years and thus should be further investigated in order to better understand and adapt to their impacts.