There  few studies done in SL refer following for tea

Assessment of impact of climate change on productivity of tea

(Camellia sinensis L.) plantations in Sri Lanka by Wijeratne et.al in 2007

Dea Asela, Thank you very much for your kind information. 

Dear Rathnayaka,

You can measure the impact of rainfall on production on tea and coconut production using the following approaches:

1] Experimental approach whereby you simulate the rainfall patterns and monitor how it impacts on  output.

2] In case you have data on yield and rainfall, you can get the relationship by regression.

Thanks.

Dennis

Dear Dennis

Thank you very much for your kind information...

To study the impact of rainfall on tea and coconut you need the following [1] there is need to collect the climatic data on rainfall amount, intensity and distribution for at least 20 years and correlate /regress the data with the yields of tea and coconut [2] I f there is deficiency of water there is need for irrigation [3] there is need to carry out soil hydraulic conductivity test, field capacity and permanent wilting point to determine available soil water[4] there is need to determine erosivity, erodibility slope and cropping systems involving tea and coconut to formulate universal loss equation as well as determining methods of controlling soil erosion and other conservation practises