I am doing a study to find climate change in a catchment. I have calculated potential Evapotranspiration for study period by using Pan evaporation method. Now I want to calculate potential Evapotranspiration for future 2050-2060 and I have GCM out put data of Temperature and Precipitation data on monthly basis. Kindly suggest me a suitable technique.
Hi:
If you have monthly values of temperature (T) and Precipitation (P) projected by a GCM for a thirty year period surrounding 2050-60, you can follow the following steps:
Step 1:
Get historical climate data for a thirty year period (if possible for 1980-2010)
Step 2:
Calculate monthly T and P for the 30 years and average for the year centered around this period that is 1995.
Step 3: Similarly compute average climate in 2055 from 2040-70 GCM data.
Step 4: Calculate climate change in 2055
For this just subtract monthly values of T and P for 1995 from 2055 values. Now you have the climate change (delta) projections for 2055.
Step 5:
Add the Delta values from above step on to the 1980-2010 monthly data and get the climate change data for 2040-70 centered around 2055.
This method of preparation of climate change data is known as the delta change method of downscaling climate change data for a location.
Step 6:
The new 1980-2010 data you can use with one of the methods for ET computation as suggested by Muller above (Thornthwaite, for example) and compute monthly ET for thirty years and average monthly. As you have modified this data with the climate change, what you get here is ET in 2055.
Hope this helps!
If you have questions, please let me know and I can help you further.
Sasi
Hi Shahid:
As you have GCM data of temperature and precipitation (2050-2060) you can also predict SPEI values for that period as an interesting way of potential climate change evaluation. In addition, you can also consult the SPEI manual were a method for estimating evapotranspiration from temp. and precip. records is available.
cheers Humberto
Hi,
there are not too many equations to calculate evapotranspiration only based on temperature. You could try the Thornthwaite method (Thornthwaite, C.W. (1948): An approach toward a rational classification of climate. - The Geogr. Rev. 38 (1): 55-94.). But, also humidity and radiation will likely change and affect evaporation - so maybe other equations should be used that take into account the effects of climate change (e.g. Priestley-Taylor, which uses T and radiation or Penman-Monteith, which indeed needs lot more input).
best,
Hannes
Hi,
I would also suggest the Hargreaves-Samani (1985) equation. If you have observed data you can also apply a bias correction of your projected Temperature data.
Cheers
Noemi
I suggest Penman-Monteith with limited climate data (Allen et al. 1998).
Hi
You may use even FAO-Penman method with assumption on some factors like wind speed as average, please see "An update for the defenition of reference evapoptranspiration" Allen et al., 1994
Hi:
If you have monthly values of temperature (T) and Precipitation (P) projected by a GCM for a thirty year period surrounding 2050-60, you can follow the following steps:
Step 1:
Get historical climate data for a thirty year period (if possible for 1980-2010)
Step 2:
Calculate monthly T and P for the 30 years and average for the year centered around this period that is 1995.
Step 3: Similarly compute average climate in 2055 from 2040-70 GCM data.
Step 4: Calculate climate change in 2055
For this just subtract monthly values of T and P for 1995 from 2055 values. Now you have the climate change (delta) projections for 2055.
Step 5:
Add the Delta values from above step on to the 1980-2010 monthly data and get the climate change data for 2040-70 centered around 2055.
This method of preparation of climate change data is known as the delta change method of downscaling climate change data for a location.
Step 6:
The new 1980-2010 data you can use with one of the methods for ET computation as suggested by Muller above (Thornthwaite, for example) and compute monthly ET for thirty years and average monthly. As you have modified this data with the climate change, what you get here is ET in 2055.
Hope this helps!
If you have questions, please let me know and I can help you further.
Sasi
You may also use limited climate data model to estimate Penman-Monteith reference evapotranspiration (Allen et al., 1998). Validations are needed. You may use for present and future climate, as wel.l
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