Abstract
Estimation of evapotranspiration (ET) for mountain ecosystem is of absolute importance since it servesas an important component in balancing the hydrologic cycle. The present study evaluates the performance of original and location specific calibrated Hargreaves equation (HARG) with the estimates of Food and Agricultural Organization (FAO) Penman Monteith (PM) method for higher altitudes in East Sikkim, India.The results show that the uncalibrated HARG model underestimates ET0 by 0.35 mm day-1 whereas the results are significantly improved by regional calibration of the model.In addition, this paperalso presents the variability in the trajectory associated with the climatic variables with the changing climate in the study site. Non-parametric Mann-Kendall (MK) test was used to investigate and understand the mean monthly trend of eight climatic parameters including reference evapotranspiration (ET0) for the period of 1985 - 2009. Trend of ET0 was estimated for the calculations done by FAO PM equation. The outcomes of the trend analysis show significant increasing (p ≤ 0.05) trend represented by higher Z-values, through MK test, for net radiation (Rn), maximum temperature (Tmax) and minimum temperature (Tmin), especially in the first months of the year. Whereas, significant (0.01 ≥ p ≤ 0.05) decreasing trend in vapor pressure deficit (VPD) and precipitation (P) is observed throughout the year. Declining trend in sunshine duration, VPD and ET0 is found in spring (March - May) and monsoon (June – November) season. The result displays significant (0.01≤p ≤ 0.05) decreasing ET0 trend between (June - December) except in July, exhibiting the positive relation with VPD followed by sunshine duration at the station.Overall, the study emphasizes the importance of trend analysis of ET0 and other climatic variables for efficient planning and managing the agricultural practices, in identifying the changes in the meteorological parameters and to accurately assess the hydrologic water balance of the hilly regions.
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