No abstract

No abstract

Abstract:In the present study, the trends in the reference evapotranspiration (ET O ) estimated through the Penman-Monteith method were investigated over the humid region of northeast (NE) India by using the Mann-Kendall (MK) test after removing the effect of significant lag-1 serial correlation from the time series of ET O by pre-whitening. During the last 22 years, ET O has been found to decrease significantly at annual and seasonal time scales for 6 sites in NE India and NE India as a whole. The seasonal decreases in ET O have, however, been more significant in the pre-monsoon season, indicating the presence of an element of a seasonal cycle. The decreases in ET O are mainly attributed to the net radiation and wind speed, which are also corroborated by the observed trends in these two parameters at almost all the times scales over most of the sites in NE India. The steady decrease in wind speed and decline in net radiation not only balanced the impact of the temperature increases on ET O , but may have actually caused the decreases in ET O over the humid region of northeast India.

No abstract

Trends in maximum (T max ), minimum (T min ) and mean (T mean ) temperatures; diurnal temperature range (DTR = T max − T min ); and sunshine duration at eight sites in Northeast (NE) India were investigated. Three sites observed decreasing trends in DTR corresponding to annual, seasonal (pre-monsoon and monsoon) and monthly (September) time scales. On the other hand, DTR increases were also observed at other three sites in monsoon and post-monsoon seasons as well as in the months of June, October and December. The sites showing DTR decreases (increases) witnessed either increasing trends in T min (T max ) or decreasing trends in T max (T min ), with T max (T min ) showing either no trend or increasing at a smaller rate than T min (T max ). Temperature remained practically trendless in winter and pre-monsoon seasons over NE India. However, temperature increases were observed in monsoon and post-monsoon seasons. Decreasing trends in sunshine duration were observed mainly on annual, seasonal (winter and pre-monsoon) and monthly (January, February and March) time scales. Concomitant decreases in sunshine duration may be one of the potential causes of the observed DTR decreases over NE India.