Hello all,
I am going to estimate forest transpiration for a forest area as it is one of the necessary components of the some hydrological models.
Since we have not access to eddy covariance flux towers, I am looking for a method that indirectly estimate forest transpiration.
My best,
Omid,
Barometer watersheds or experimental catchments are sometimes used to develop water balances to use precipitation inputs and stream discharge outputs, considering soil moisture change to help identify unknowns such as evapotranspiration. There are some ET models such as developed by Thornthewaite-Mather, Penman and others that employ various factors such as temperature, humidity, wind, soil moisture, solar radiation or other factors. Various publications developed at hydrological research stations have come up with estimates of ET using water balance methods, and sometimes comparing with various emperical models. One of the publications developed at Coweeta Hydrologic Station in NC using various forested and grassland catchments indicated that ET for pine forests was approximately from memory about 30 inches, hardwoods 20 inches and grasslands 10 inches annually using water balance approach. Comparing species or forest stands relative to leaf area index is sometimes helpful. Various lysimeter studies have been undertaken to measure transpiration responses of select tree or plant species to soil moisture change, solar radiation, temp, etc.
Concerning water balances, it becomes obvious in many moderate to low rainfall circumstances that ET has a higher value than runoff (stream discharge). ET is just so much more difficult to study and quantify, than installing a streamflow gauge and rain gauges within a watershed. I did not mention deep seepage losses that may occur in some circumstances, such as karst, lithologically fractured or conditions of loosing streams. As my experience is dated, I do not know if there are recent models.
Hi Omid
I suggest you to talk more about Evapotranspiration rather than Transpiration.
With the absence of direct measurements, you can use simple models dreived from Penman-Monteith euqation. More details can be found in the FAO-56 Report: https://www.kimberly.uidaho.edu/water/fao56/fao56.pdf
Rachid
i think the utilizing of thornthwate evapotranspiration equation is optimum for your region
Probably using Vegetation Index from hyper-spectral data could be useful to estimate transpiration by photosynthesis rate, water content among others. There are instrumentation on-ground as well as satellite as mention Prof. HAMIMED Abderrahmane
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