Rising mean and extreme near‐surface air temperature across Nepal

• Published in: International Journal of Climatology Vol. 40; no. 4; pp. 2445 - 2463
• Main Authors: Karki, Ramchandra, ul Hasson, Shabeh, Gerlitz, Lars, Talchabhadel, Rocky, Schickhoff, Udo, Scholten, Thomas, Böhner, Jürgen
• Format: Journal Article
• Language: English
• Published: Chichester, UK Wiley 30.03.2020; John Wiley & Sons, Ltd; Wiley Subscription Services, Inc
• Subjects: Adaptation; Air temperature; Anomalies; Anticyclonic circulation; Biodiversity; Climate change; climatic extremes; Cloud cover; Cold days; Cooling; Daily temperatures; Disasters; Dynamic height; Environmental impact; Fog; Geopotential; Geopotential height; Height anomalies; Himalayas; increase in warm days and nights; Lower atmosphere; Lowlands; Maximum temperatures; Minimum temperatures; Monsoons; Mountain regions; Mountains; Natural disasters; Nepal; Seasons; Snowfall; Stability; Surface-air temperature relationships; Temperature changes; Temperature extremes; Temperature trends; Troposphere; Upper troposphere; Valleys; Wind; Winter; Nepal
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.6344

Owing to unique topographic and ecological diversity, central Himalayan state of Nepal is exposed to adverse impacts of climate change and associated disasters. However, countrywide historical assessment of mean and extreme temperature changes, a prerequisite for devising adequate adaptation strategies, is still lacking. Here, we present a comprehensive picture of mean and extreme temperature trends across Nepal over the 1980–2016 period, based on high‐quality daily temperature observations from 46 stations. Our results suggest that besides winter cooling in southern lowlands, the country features a widespread warming, which is higher for maximum temperature (~0.04°C⋅year−1) than for minimum temperature (~0.02°C⋅year−1), over the mountainous region than in valleys and lowlands and during the pre‐monsoon season than for the rest of the year. Consistently, we found a higher increasing trend for warm days (13 days⋅decade−1) than for warm nights (4 days⋅decade−1), whereas the rates of decrease for cold days and cold nights are the same (6 days⋅decade−1). Further investigations reveal that pronounced warming in maximum temperature over mountain regions can be attributed to less cloud cover and snowfall in recent decades during non‐monsoon seasons as a result of positive geopotential height anomalies and strengthening of anticyclonic circulations in the mid‐to‐upper troposphere. Similarly, increased stability of lower atmosphere during winter and post‐monsoon seasons caused prolonged and frequent periods of fog over lowlands, resulting in significant winter cooling there. (a) Location of Nepal. Political boundary is shown by magenta polygon. Topography is shaded in grey, (b) three broad physiographic regions of Nepal, such as, lowlands, middle mountains and hills, and high mountains are shown in polylines and the terrain shaded in grey, and (c) mean annual normal maximum temperature (°C) and location of 46 stations used in this study.