A web search will find plenty of material.

Try this:

https://eng.ucmerced.edu/people/rbales/CV/PubsM/98

This study examines the air temperature/stream temperature relationship at a geographically diverse set of streams. We evaluate the general temperature relationships (both linear and nonlinear) that apply to these streams, and then examine how changes in stream temperature associated with climate variability or climate warming might affect dissolved oxygen levels. The majority of streams showed an increase in water temperature of about 0.6–0.8°C for every 1°C increase in air temperature, with very few streams displaying a linear 1:1 air/water temperature trend. For most of the streams, a nonlinear model produced a better fit than did a simple linear model. Understanding the relationship between air temperature and water temperature is important if people want to estimate how stream temperatures are likely to respond to anticipated future increases in surface air temperature. Surface water temperature in many streams will likely increase 2 to 3°C as air temperature increases 3 to 5°C. At sites with currently low dissolved oxygen content, an increase in summer stream temperatures could cause the dissolved oxygen levels to fall into a critically low range, threatening the health of many aquatic species. - See more at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9372(2005)131%3A1(139)#sthash.muGeoZey.dpuf

Dear Paride,

Here are some documents that can be very useful.

https://www.researchgate.net/publication/227981034_Stream_Temperature_Estimation_from_Air_Temperature

https://eng.ucmerced.edu/people/rbales/CV/PubsM/98

https://www.env.nm.gov/swqb/protocols/2011/Air-Water08-01-2011.pdf

http://www.hydrol-earth-syst-sci.net/17/3323/2013/hess-17-3323-2013.pdf

With my best regards

Prof. Bachir ACHOUR

Article Stream Temperature Estimation from Air Temperature

Thanks to all for the useful links.