Spatio-temporal variations of reference evapotranspiration using Innovative and Mann-Kendall trend analysis under limited weather data in semi-arid region of Indian Punjab

The trend detection in hydro-climatological series is a prime priority in the context of changing climate. Evapotranspiration is a crucial component of the hydrological cycle and surface energy balance that plays a key role in irrigation water management. The present study examined the spatio-temporal variations of annual and seasonal reference evapotranspiration using Mann-Kendall and Innovative trend analysis, in South West and central part of Punjab over the period of 1980-2021. The results revealed that reference evapotranspiration (RET) for the annual, pre-monsoon, and post-monsoon series at Sangrur (Central Zone) and for winter at Bathinda (South-West) were serially correlated using the autocorrelation test of lag-1 at a 5% significance level. The highest aridity index (0.34 +/- 0.10) and the lowest moisture index (-0.66 +/- 0.10) were detected at Moga station, followed by Sangrur station in Central Punjab. The overall results revealed that annual and seasonal trend of reference evapotranspiration was significantly decreasing over the period 1980-2021. The spatial distribution of Sen's slope percentage change was highest at Mansa station, followed by Sangrur station. Mann-Kendall trend analysis of annual and post-monsoon series revealed that out of a total of six stations, Barnala, Muktsar Sahib, and Sangrur showed a significant decreasing trend. The Sen's slope and ITA trend slope of monsoon series are statistically decreasing at 1% and 5% significance level all over the districts. In the pre-monsoon season, an increasing trend of RET was detected throughout all the stations, with the highest percentage change of 4.3% detected at Mansa station. The ITA trend slope of ET0 exhibited decreasing magnitude in the annual, monsoon, post monsoon except at pre-monsoon season all round the districts. While the contrasting trend is found in MK slope exhibited increasing and decreasing trend in the pre-monsoon season. The innovative trend slope revealed the presence of a hidden trend for RET that was missed by the traditional MK/MMK test. The study may guide planners and policymakers in the effective implementation of crop water management strategies to improve the status of water resources in Punjab.