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

Abstract

This study aims to assess the accuracy of two satellite‐based precipitation products (SBPPs), that is, Tropical Rainfall Measurement Mission (TRMM)‐based Multi‐satellite Precipitation Analysis (TMPA) and its upgraded version Integrated Multi‐Satellite Retrievals for Global Precipitation Measurement (IMERG), in capturing spatial and temporal variation of precipitation and their application for extreme events (high‐intensity precipitation and drought). They were evaluated against 142‐gauge stations from Nepal during 2001–2018. The results show that, in general, both SBPPs show the overall characteristics of precipitation patterns, although underestimated the mean annual precipitation during the study period. It was also noted that IMERG product yields better performance to detect precipitation events (probability of detection) and no‐precipitation events (false alarm ratio) than TMPA. Based on four different extreme precipitation indices: heavy precipitation events (R10mm), extreme precipitation events (R25mm), five consecutive dry days (CDD), and five consecutive wet days (CWD), it was observed that the SBPPs underestimated the frequency of R25mm and CDD spells while overestimated R10mm and CWD spells. Additionally, both SBPPs exhibited considerable capabilities in capturing the drought events during the study period. Overall, the drought event, bias, and frequency show that the IMERG product has slightly better capabilities to capture drought than the TMPA product. In general, IMERG was found to be superior at a daily timescale, while TMPA shows consistent performance on a monthly scale during the study period. Furthermore, there is still space for further improvement of IMERG rainfall retrieval algorithms.

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

“…This discrepancy may partially result from inaccurate precipitation measurements, especially for solid precipitation; 63 we report that more recent (2016-2019) mean annual precipitation data from a shielded weighing precipitation gauge (587 mm; Table S1) are considerably higher than totals reported from an unshielded and unheated tipping bucket (449 mm) at Pyramid (1994-2012). 21 In general, our measurements of precipitation by season are in excellent agreement with previous studies in the Khumbu 27 and in the broader Nepal Himalaya, 6,19,20 with 75%-80% of the annual precipitation on average falling during the monsoon. driving precipitation at the heart of the Himalayan water tower, of vital importance to local residents and the environment and communities downstream.…”

“…An in-depth assessment of precipitation in the Khumbu region in the central Himalaya ( Figure 1) highlights some key vulnerabilities, as up to 56% of the domestic water supply for the more than 6,000 residents comes from rainwater, 4 and locals and tourists alike suffer from precipitation extremes resulting in impassable and washed-out trails. 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).…”

Spatial Distribution of Extreme Precipitation Events and Its Trend in Nepal

“…Some basin level study also reported the decrease in average annual precipitation over the Koshi basin from 1997 to 2016 [15]. Moreover, Reference [16] evaluated the TRMM product and found that TRMM precipitation product is good alternative to gauge observation over Nepal. Further, precipitation and its extremities pattern change over time and continuous analysis is need to monitor such events.…”

“…Such extreme precipitation events have broad societal impacts and appear to be increasing with ongoing climate change. For instance, the cloudburst of 14-17 June 2013 in the northwestern mountainous region near the Nepalese border [11], a massive rainfall event of [14][15][16] August 2014, [29][30] July 2019, 15-20 July 2020 have caused massive flooding and triggered several landslides, resulting in huge losses of life and property, affecting millions of households across the country. Thus, it is essential to monitor the precipitation extremes to minimize the losses.…”

Evaluation of the TRMM Product for Spatio-temporal Characteristics of Precipitation over Nepal (1998-2018)

“…Besides these studies, a few other studies have evaluated the satellite-based precipitation product. Recently, Sharma et al (2020d) found that TRMM product has similar performance as compared to new generation IMERG product across the country, while Duncan and Biggs (2012) found that TRMM product generally overestimated the precipitation values as compared to a gauge-based gridded product over Nepal.…”