Ground‐Based Observations Reveal Unique Valley Precipitation Patterns in the Central Himalaya

Abstract

While the Himalayas act as a natural barrier to water vapor transport to the Tibetan Plateau, many north‐south‐oriented valleys channel moisture onto the Plateau. However, owing to the lack of in situ data, the spatiotemporal characteristics of precipitation remain unclear along these valleys. In this study, a high‐altitude (2,800–4,500 m above mean sea level) rain‐gauge network was established in the Yadong Valley, one of the main valleys in the central Himalayan Region (CHR). New observations from this network are used to evaluate the Integrated Multi‐satellitE Retrieval for Global Precipitation Measurement (IMERG) precipitation product, with results demonstrating that the IMERG data can reproduce the seasonal and diurnal patterns of precipitation seen in the observational data. This combination of in situ and IMERG precipitation data reveals two unique characteristics in the CHR. First, precipitation during the premonsoon season (March‐May) contributes 20–40% of the annual total, from the high altitudes of the CHR to Southeast Tibetan Plateau, due to water vapor flux conveyed by southwesterlies from the Bay of Bengal, whereas this percentage is much lower in the northern Himalaya and South Asia. Second, diurnal variations in precipitation during the monsoon season (June‐September) vary between the low and high altitudes of the north‐south‐oriented valleys in the CHR: Precipitation at high altitudes has two peaks (one in the afternoon and the other at night), which is different from the single nighttime peak in low altitudes that is usually reported. These two notable spatiotemporal characteristics are indicative of the unique climate that exists at the high altitudes of the CHR.

Precipitation Characteristics and Moisture Source Regions on Mt. Everest in the Khumbu, Nepal

“…An understanding of the physical processes driving precipitation is critical for interpreting observed trends and estimating likely future changes. In this context, we observe that precipitation occurrence exhibits a nighttime peak ( Figures 5A, 5C, and 5E), which is consistent with other locations across the central Himalaya, [22][23][24][25][26]28 and in general agreement with previous findings from the Khumbu. 49 Our results indicate that the peak precipitation frequency occurs near or shortly after mean sunset at Pyramid and Pheriche ($1300-1430 UTC) and just after local midnight ($2100 UTC) at Phortse.…”

“…The increase in pre-monsoon contributions to annual precipitation from 10% at Chaurikhark (2,642 m asl) to 17% at Pyramid (5,035 m asl) is noteworthy and broadly consistent-although reduced in magnitude-with the relatively greater importance of the pre-monsoon precipitation at higher elevations in the Yadong Valley. 28…”

“…18 Existing understanding identifies that precipitation across this region is subject to considerable temporal variability, with 70%-80% of annual totals falling during the summer monsoon period of June-September, [19][20][21] when precipitation mostly falls at night. [22][23][24][25][26][27] Ouyang et al 28 report 50%-60% of annual precipitation falling during the monsoon in the Yadong Valley in the central Himalaya of China, with an afternoon peak in precipitation timing at higher elevations (>3,500 m above sea level Locations of precipitation data sources (filled squares, circles, and triangles) in the context of topography (shading), glacierized area (aqua shading), forest cover (green), and main trekking route to Everest Base Camp (dashes). The grid squares for ERA5 data presented are also shown (green and purple rectangles).…”

How Accurately Can Satellite Products (TMPA and IMERG) Detect Precipitation Patterns, Extremities, and Drought Across the Nepalese Himalaya?

“…The rain gauges conventionally provide in situ measurements, although they have various limitations yet provide a real estimate at a point scale (Sun et al, 2018; Yamamoto et al, 2011). The use of gridded satellite‐based precipitation products (SBPPs) overcomes such limitations rendered by the low spatial density of gauge stations (Derin et al, 2019; Ouyang et al, 2020; Wang & Yong, 2020). Various satellite missions provide remotely sensed real‐time, nearly real‐time, and posttime gridded estimates of precipitation (Sun et al, 2018).…”

Twice‐Daily Monsoon Precipitation Maxima in the Himalayas Driven by Land Surface Effects

“…See the text for rain gauge stations. (Ueno et al 2008;Yang et al, 2018), and from five surface stations at altitudes ranging from 3,341 to 4,321 m asl along a valley in the Himalayas at around 89°E (Ouyang et al, 2020). In contrast, in situ observations made at 3,570, 3,833, and 4,260 m asl in Khumbu Valley, and at Khudi at 780 m asl and other stations below 1,500 m asl in the Marsyandi river basin, show a single peak for precipitation, which corresponds to nighttime (Barros et al, 2000;Ueno et al, 2001Ueno et al, , 2008Yang et al, 2018).…”