Seasonal Contrast in Precipitation Mechanisms over Nepal Deduced from Relationship with the Large-Scale Climate Patterns

Abstract

Summer precipitation dominates over winter one for the annual total in south Asia, while the winter condition is still important for agricultural productions. Rain gauge data over Nepal were analyzed with large-scale atmospheric patterns such as El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). In the period of June to September, summer monsoon rainfall over Nepal (SMRN) is generally higher in the eastern region along with a peak in the central region associated with the local orography. Its interannual variability was found to be correlated with the southern oscillation index (SOI): i.e., when La Niña occurs, eastward moisture flux is blocked over Bay of Bengal (BOB) by the anomalous Walker circulation extending from the Pacific. The local-scale condition for higher SMRN is implied by a main moisture route along the eastern arm of the low pressure in northeastern India, as proved by a significant correlation between SMRN and the northward moisture flux. In winter (DJFM), precipitation occurs more in the western region. The higher winter precipitation over Nepal (WPN) was correlated almost equally with positive Dipole Mode Index (DMI) over the Indian Ocean and also SOI, while the relationship with SOI is reversed from summer. A clear linkage was suggested with moisture flux from the Arabian Sea and the further western region. Thus, possible impacts of anomalous precipitation have to be predicted under the relationship with the large-scale indices depending on seasons.

Projected distribution and climate refugia of endangered Kashmir musk deer Moschus cupreus in greater Himalaya, South Asia

“…In the southern Himalaya, moisture comes from precipitation arising from the Indian Ocean mainly during summer, making high rainfall in the eastern Himalaya leaving the western Himalaya drier than eastern Himalaya. During winter, the westerly winds from the Mediterranean sea brings more precipitation in the form of snow to the western Himalaya, but less to the eastern Himalaya 48 . The massive mountain range acts as a barrier to air flow from south to north, resulting in a dry and treeless Tibet 49 .…”

“…Western disturbances from the west arise from the Mediterranean Sea and dominate the climate of western Himalaya during winter. During summer, the dominant weather pattern is driven by moisture arising from the Indian Ocean 48,72,73 . In Uttarakhand and west Nepal, the climate is different than Kashmir and Pak-Afghan as it is influenced by both south west monsoon and westerly storms 74 .…”

Spatial and Temporal Variation of Drought Based on Satellite Derived Vegetation Condition Index in Nepal from 1982–2015

“…Drought in Nepal is due to the country’s high climatic variation with volatile temperature and precipitation patterns in the elevation ranging from the low altitudinal zone at 60 m in the south to a high altitude at 8848 m above sea level in the north. About 80% of the total annual precipitation occurs during summer [20] while the winter precipitation only contributes 3% of total annual precipitation [21]. The rainfall distribution patterns are erratic and spatially varied due to an orographic effects and influences of the Asian monsoon which cause southern and eastern parts to receive more rainfall while northern and western parts receive less [22].…”

Drought risk assessment in central Nepal: temporal and spatial analysis

“…In Nepal about 80 % of the total annual rainfall occurs during the summer monsoon (June-September) (Shrestha 2000), which is the most important season for agriculture because summer crops (paddy, maize and millet) comprise nearly 80 % of the total national cereal production (Gautam and Regmi 2013). Although the summer monsoon dominates the total precipitation in Nepal, the winter precipitation, which contributes 3 % of total annual precipitation, is still important for agricultural production (Sigdel and Ikeda 2012).…”