Water Temperature Forecast in Castelo do Bode Reservoir

The blog castelodebode.blogspot.com conducted a study in order to get from a quick way the water temperature in Castelo do Bode reservoir, from the air temperature. For that daily measurements of water temperature were carried out on the reservoir and compared with air temperature during the year of 2012.The values of water temperature depend on many external factors that are not constant from day to day and therefore an estimate of water temperature has always an associated error. During 2012 the monthly average water temperature recorded at the beginning of the day on the reservoir ranged between 11.6ºC for February and 24.3ºC in August. On the other hand, the average monthly air temperature ranged between 6.9ºC for February and 22.3ºC in August.

Based on the data obtained, the best formula for the water temperature in the beginning of the day, on the reservoir, was built with mean air temperature of the previous day as variable: 

T_w = 0.7T_A(-1) + 7.71

Where: 

T_w – Water temperature in the reservoir in the early hours of the day; 

T_A(-1) – Average air temperature of the day before at the Castelo do Bode reservoir area.  

As the water reservoir temperature is not constant throughout the day it was necessary to introduce an additional element to the above formula to find the water temperature at a certain time of the day. Although the relation of water temperature with air temperature is not constant during the day, as an approach may be considered that for each 1ºC that the air temperature rises or falls during the day, the water temperature rises or falls 0.1ºC.Despite the formula found have an associated average error of 1.7ºC, it can be concluded that in 90% of 2012 year the average water temperature in Castelo do Bode reservoir was higher than the average air temperature.The water temperature in the reservoir is a very important characteristic for recreational and biological activities that are practiced during the summer months. Therefore all reservoir users have now one more way at their disposal to know the water temperature.  

You can download the paper here