Abstract
Abstract. Long-term monitoring of snow cover is crucial for climatic and hydrological studies. The utility of long-term snow-cover products lies in their ability to record the real states of the earth's surface. Although a long-term, consistent snow product derived from the ESA CCI+ (Climate Change Initiative) AVHRR GAC (Advanced Very High Resolution Radiometer global area coverage) dataset dating back to the 1980s has been generated and released, its accuracy and consistency have not been extensively evaluated. Here, we extensively validate the AVHRR GAC snow-cover extent dataset for the mountainous Hindu Kush Himalayan (HKH) region due to its high importance for climate change impact and adaptation studies. The sensor-to-sensor consistency was first investigated using a snow dataset based on long-term in situ stations (1982–2013). Also, this includes a study on the dependence of AVHRR snow-cover accuracy related to snow depth. Furthermore, in order to increase the spatial coverage of validation and explore the influences of land-cover type, elevation, slope, aspect, and topographical variability in the accuracy of AVHRR snow extent, a comparison with Landsat Thematic Mapper (TM) data was included. Finally, the performance of the AVHRR GAC snow-cover dataset was also compared to the MODIS (MOD10A1 V006) product. Our analysis shows an overall accuracy of 94 % in comparison with in situ station data, which is the same with MOD10A1 V006. Using a ±3 d temporal filter caused a slight decrease in accuracy (from 94 % to 92 %). Validation against Landsat TM data over the area with a wide range of conditions (i.e., elevation, topography, and land cover) indicated overall root mean square errors (RMSEs) of about 13.27 % and 16 % and overall biases of about −5.83 % and −7.13 % for the AVHRR GAC raw and gap-filled snow datasets, respectively. It can be concluded that the here validated AVHRR GAC snow-cover climatology is a highly valuable and powerful dataset to assess environmental changes in the HKH region due to its good quality, unique temporal coverage (1982–2019), and inter-sensor/satellite consistency.
Highlights
Snow cover is an important indicator to estimate climatic changes and a key input for climate, atmospheric, hydrological, and ecosystem models (Fletcher et al, 2009; Hüsler et al, 2012; Xiao et al, 2018)
This paper presents the validation of the AVHRR GAC snow product over the Hindu Kush Himalayan (HKH) area during snow seasons
The validation was conducted from two aspects: (i) one is based on 197 scenes covering the whole HKH region in order to increase the spatial coverage of validation, and (ii) the other is based on 46 · 2 scenes over P140-R40/41 in order to make a detailed analysis of the factors influencing the accuracy of the AVHRR snow dataset
Summary
Snow cover is an important indicator to estimate climatic changes and a key input for climate, atmospheric, hydrological, and ecosystem models (Fletcher et al, 2009; Hüsler et al, 2012; Xiao et al, 2018). Snow cover exacerbates the effect of global warming through the positive feedback between snow and albedo (Serreze and Francis, 2006). It affects the hydrometeorological balance through snowmelt (Simpson et al, 1998). Snow cover is severely affected by climate change due to its high sensitivity to changes in temperature and precipitation (Brown and Mote, 2009). Wu et al.: Evaluation of snow extent time series in the Hindu Kush Himalayas ment decisions, and investigating climate change impacts on environmental variables (Arsenault et al, 2014; Sun et al, 2020)
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