Elevation-dependent warming of maximum air temperature in Nepal during 1976–2015

Abstract

Significant elevation-dependent warming (EDW) of maximum near-surface air temperature and diurnal temperature range (DTR) has been observed in Nepal (southern central Himalaya) until 2566 m a.s.l., over the last four decades (1976–2015). During this period, on the average and across the entire country, maximum air temperature increased (+0.045 °C y−1, p < .001) more than minimum temperature (+0.009 °C y−1, p < .05) and, as a consequence, DTR also increased significantly (+0.034 °C y−1, p < .001). Maximum temperature increases have been observed during all seasons of the year. This warming pattern differs from the symmetrical one observed at global level in the same period, and it is in contrast to more prominent minimum temperature increases observed in the north of Himalaya (Tibetan Plateau). Furthermore, the near-surface air temperature change observed in Nepal contrasts the global evidence of main increasing trends occurring during the winter months. We point out that this asymmetric warming pattern could have more serious impacts in Nepal than in other regions of the world, considering the consequences of associated warm maximum-temperature extremes (heatwaves, hot days) on human life, increased primary production, and modifications in the hydrological cycle. We conclude sustaining that the observed EDW of maximum temperature and the DTR could be attributed to the monsoon weakening, namely to the reduced number of rainy days observed in the region during the last decades. These phenomena could have been accompanied by decreasing cloudiness and consequent increasing of daytime shortwave and decreasing of nighttime longwave incoming solar radiation.