Evaluation of MERRA-2 Precipitation Products Using Gauge Observation in Nepal

Abstract

Precipitation is the most important variable in the climate system and the dominant driver of land surface hydrologic conditions. Rain gauge measurement provides precipitation estimates on the ground surface; however, these measurements are sparse, especially in the high-elevation areas of Nepal. Reanalysis datasets are the potential alternative for precipitation measurement, although it must be evaluated and validated before use. This study evaluates the performance of second-generation Modern-ERA Retrospective analysis for Research and Applications (MERRA-2) datasets with the 141-gauge observations from Nepal between 2000 and 2018 on monthly, seasonal, and annual timescales. Different statistical measures based on the Correlation Coefficient (R), Mean Bias (MB), Root-Mean-Square Error (RMSE), and Nash–Sutcliffe efficiency (NSE) were adopted to determine the performance of both MERRA-2 datasets. The results revealed that gauge calibrated (MERRA-C) underestimated, whereas model-only (MERRA-NC) overestimated the observed seasonal cycle of precipitation. However, both datasets were able to reproduce seasonal precipitation cycle with a high correlation (R ≥ 0.95), as revealed by observation. MERRA-C datasets showed a more consistent spatial performance (higher R-value) to the observed datasets than MERRA-NC, while MERRA-NC is more reasonable to estimate precipitation amount (lower MB) across the country. Both MERRA-2 datasets performed better in winter, post-monsoon, and pre-monsoon than in summer monsoon. Moreover, MERRA-NC overestimated the observed precipitation in mid and high-elevation areas, whereas MERRA-C severely underestimated at most of the stations throughout all seasons. Among both datasets, MERRA-C was only able to reproduce the observed elevation dependency pattern. Furthermore, uncertainties in MERRA-2 precipitation products mentioned above are still worthy of attention by data developers and users.

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).…”

Assessment of drought impacts on crop yields across Nepal during 1987–2017

“…Regionally, central and eastern Nepal receives more monsoonal precipitation in summer, while the western region receives the highest westerly precipitation in winter (Sharma et al ., 2020a). Moreover, the distribution of precipitation is determined by local scale parameters, such as orography, wind exposure and direction of the mountain range (Hamal et al ., 2020b). During the La Niña years, the moisture divergence with strong northwesterly wind anomalies drives the dry winter years across Nepal (Hamal et al ., 2020a).…”

Dynamics of Maximum Snow Cover Area and Snow Line Altitude Across Nepal (2003-2018) Using Improved MODIS Data

“…For this study, we divided Nepal into the Western, Central, and Eastern regions based on the major river basins (the Karnali, Gandaki, and Koshi, respectively) and the duration and timing of monsoonal climatology ( Fig. 1) (Hamal et al, 2020b).…”