Assessing the Long-Term Changes in Potential Evapotranspiration and its Impact on Agriculture in Lahaul and Spiti, Himachal Pradesh

Abstract

Long-term variations in Potential Evapotranspiration (PET) hold importance in evaluating climate changes impacting agriculture in sensitive high-altitude regions. The study intends to observe the PET temporal trends between 1951 and 2022 and study the agricultural implications for the cold desert district of Lahaul and Spiti in the Indian State of Himachal Pradesh. Monthly PET data were taken from the CRU TS v4.07 dataset and calculated using the FAO Penman-Monteith method. The non-parametric statistical tests used for detecting seasonal and annual trends are the Mann-Kendall test, the Modified Mann-Kendall test, and the Innovative Trend Analysis method. The increases and decreases across all seasons were statistically significant, with the strongest negative trend seen during the agricultural season (April–October), with MK Z-values ranging from –6.47 to –2.92 and m-MK values ranging from –12.16 to –2.14. The annual trend also declined, with the highest decrease reported at Grid Point 1 (Z = –7.04; magnitude = –0.0030 mm/year). With these results, the demand for atmospheric water is assumed to be declining, which might lead to a reduction in crop irrigation needs, thereby increasing soil moisture availability. On the other hand, an increase in relative humidity and shifting cropping patterns might lead to increased chances of disease risks and stress in nutrient uptake. The study stresses the need to plan adaptive water and crop management strategies that conform to the changing PET scenario.