Abstract
Trends in reference evapotranspiration (ETo) estimated using Penman-Monteith equation were analysed over arid, semi-arid and humid regions of northwest (NW) India during 1985–2018. The MannKendall is used to determine significance of trends. Theil-Sen’s estimator and least square linear fitting methods are adopted to find slopes of the trend lines. The results indicated a significant decrease in ETo on annual basis for most of the locations and NW India as a whole. However, the trend was not statisticallysignificant for seasonal ETo. The significant decrease in solar radiation and wind speed nullified the impact of increased temperature and resulted in slight decrease in ETo over arid and semi-arid regions of NW India which could probably be attributed to the increased dust hazy conditions prevailing. In NW India, water is a limiting resource the decrease in ETo may help researchers in decision makers to develop water assets and utilize the irrigation systems more effectively. There was also an increasing trend in production of major crops in the study region. Further, in near future, if this decreasing ETo trend were to remain, it would help in intensification of cropping system with the existing water resource.
Highlights
According to the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC, 2007), there was an increase of 0.74 0C in the global mean air temperature during past 100 years and it is projected to increase by 1.1 to 6.40C by 2100
The semi-arid region covers the middle districts like Jaipur, Ajmer, Tonk while humid region covers the eastern districts Dholpur, Sawai Madhopur, Bhilwara, Chittorgarh, Udaipur, Dungarpur, Banswara and Kota
Seasonal analysis revealed that the mean annual ETo values during pre-monsoon and monsoon seasons observed in the arid region were 560.1 mm and 681.4 mm with highe r% contribution of Hanumangarh district
Summary
According to the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC, 2007), there was an increase of 0.74 0C in the global mean air temperature during past 100 years and it is projected to increase by 1.1 to 6.40C by 2100. Seasonal analysis revealed that the mean annual ETo values during pre-monsoon and monsoon seasons observed in the arid region were 560.1 mm and 681.4 mm with highe r% contribution of Hanumangarh district. Maximum ETo is observed during monsoon season all across the study sites because of relatively higher average temperatures, solar radiation and rainfall.
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