Abstract:
In this study, reference evapotranspiration (ETo)
has been estimated using Penman–Monteith (PM) method on
monthly time step. The monthly values have been subsequently
used to estimate annual and seasonal ETo values. The
trend analysis has been carried out for monthly, annual and
seasonal ETo values for three meteorological stations namely
Allahabad,Rewa and Satna located in the Tons River Basin in
Central India. Further, the trend of weather variables that
affect ETo have been examined using the Mann–Kendall test
after removing the effect of significant lag-1 serial correlation
from the time series using trend free-pre-whitening (TFPW)
method. The magnitude of trends has been calculated using
Sen’s slope estimator. Almost all the months show the significant
decreasing trend in ETo values at a significance level
of 1, 5 and 10 %. The significant decreasing trends were also
found in annual and seasonal ETo values during the period of
analysis. The magnitude of decrease in annual ETo varied
from -1.75 to -8.98 mm/year. On the seasonal scale, stronger
decreasing trends were identified in ETo in pre monsoon
and monsoon season as compare to that of winter and post
monsoon season. The significant decreasing trends were
found in monthly, annual and seasonal wind speed. However,
significant increase was found in annual air temperature
(maximum, minimum, mean and dew point temperature) and
relative humidity. Using the sensitivity analysis, maximum
temperature and net solar radiation was found to be the most
dominant variables which influence the rate of annual ETo
over all the stations.
