Spatial Pattern of Precipitation in GPM-Era Satellite Products against Rain Gauge Measurements over Nepal

Abstract

Precipitation in a mountainous region is highly variable due to the complex terrain. Satellite-based precipitation estimates are potential alternatives to gauge measurements in these regions, as these typical measurements are not available or are scarce in high elevation areas. However, the accuracy of these gridded precipitation datasets need to be addressed before further usage. In this study, an evaluation of the spatial precipitation pattern in satellite-based precipitation products is provided, including satellite-only (Integrated Multi satellite Retrievals for GPM IMERG-UCORR and Global Satellite Mapping of Precipitation (GSMaP-MVK) and gauge calibrated (IMERG-CORR and GSMaP-Gauge) products, with a spatial resolution of 0.1°, which is compared to 387-gauge measurements in Nepal from April 2014 to December 2016. The major results are as follows: (1) The gauge calibrated version 5 IMERG-CORR and version 6 GSMaP-Gauge are relatively better than the satellite-only datasets, although they all underestimate the observed precipitation. (2) The daily gauge calibrated GSMaP-Gauge performs fairly well in low and mid-elevation areas, whereas the monthly gauge calibrated IMERG-C performs better in high-elevation areas. (3) For the daily time scale, IMERG-CORR shows a better ability to detect the true precipitation (higher Probability of Detection (POD)) and (lowest False Alarm Ratio (FAR)) events among all datasets. However, all four satellite-based precipitation datasets accurately detect (Critical Success Index (CSI) >40%) precipitation and no-precipitation events. The results of this work provide the systematic quantification of IMERG and GSMaP of satellite precipitation products over Nepal using station observations and delivers a helpful statistical basis for the selection of these datasets for future scientific research.

Evaluation of Satellite-Derived Precipitation Products for Streamflow Simulation of a Mountainous Himalayan Watershed: A Study of Myagdi Khola in Kali Gandaki Basin, Nepal

“…Summer monsoons and westerlies are Nepal's two dominant weather systems [70]. Most of the annual precipitation in Nepal falls during the monsoon period (June-September), and the rest falls during the pre-monsoon (March-May), post-monsoon (October-November), and winter (December-February) periods [14,70]. Due to the topographical differences, Nepal's mountainous regions receive less rainfall than other regions.…”

“…Precipitation data are essential for hydrological modeling [5,7,8], used in hydraulic studies [9], environmental studies [10][11][12], and climate change investigations [5]. Obtaining accurate and reliable precipitation data in remote and rugged areas, such as mountainous regions, is particularly challenging due to the high spatial and temporal variability of data, the sparse and irregular distribution of rain gauge networks, the inadequate spatial representation of in situ measurements, and the failure of climate stations due to natural disasters [7,13,14]. Satellite products have gained popularity for estimating or measuring precipitation and simulating streamflow in recent decades [6,8,[15][16][17].…”

“…The use of satellite-derived precipitation products (SPPs) is promising for supporting improved water resources management in Nepal, particularly the Himalayan region. The Himalayas make up almost 85% of Nepal's terrain, and the water reservoirs are the main source of several rivers providing water to millions of people residing in the downstream areas [14,21,22]. Due to Nepal's complex geography, the summer monsoon system governs most of the country's precipitation [14,23,24].…”

“…The Himalayas make up almost 85% of Nepal's terrain, and the water reservoirs are the main source of several rivers providing water to millions of people residing in the downstream areas [14,21,22]. Due to Nepal's complex geography, the summer monsoon system governs most of the country's precipitation [14,23,24]. The number of rain gauge-based stations in most mountain areas, particularly in high-elevation areas of Nepal, is significantly lower compared with low-elevation areas.…”

“…Ref. [14] evaluated the spatial patterns in satellite-only and gauge-calibrated precipitation products and compared them with 387-gauge measurements in Nepal. Ref.…”