Glacier melting and precipitation trends detected by surface area

Climatic time series for high-elevation Himalayan regions are decidedly scarce. Although 8 glacier shrinkage is now sufficiently well described, the changes in precipitation and temperature at these 9 elevations are less clear. This contribution shows that the surface area variations of unconnected glacial 10 ponds, i.e., ponds not directly connected to glaciers, can be considered suitable proxies for detecting 11 changes in the main hydrological components of the water balance on the south side of Mt. Everest. 12 Glacier melt and precipitation trends have been inferred by analyzing the surface area variations of ponds 13 with various degrees of glacial coverage within the basin. In general, unconnected ponds over the last 14 fifty years (1963-2013 period) have decreased significantly by approximately 10%. We inferred an 15 increase in precipitation occurred until the mid-1990s followed by a decrease until recent years. Until the 16 1990s, glacier melt was constant. An increase occurred in the early 2000s, and in the recent years, 17 contrasting the observed glacier reduction, a declining trend in maximum temperature has decreased the 18 glacier melt. 19

on the absence of cloud cover for all images, and the largest lakes with various degrees of glacial Figure 3, the inter-annual analysis is not affected by intra-annual seasonality. Consequently all images for 164 the inter-annual analysis have been selected from these months (Table SI1; Table SI2).  Table SI2.

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Detailed information of digitization methods are described in Thakuri et al., 2014. 170 To simulate the daily melting of the glaciers associated with the 10 selected ponds, we used a simple 171 T-index model (Hock, 2003). This model is able to generate daily melting discharges as a function of   respectively) and the large data gaps of the SRTM DEM in this study area (Bolch et al., 2011).

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All of the imagery and maps were co-registered in the same coordinate system of WGS 1984 UTM

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Zone 45N. The Landsat scenes were provided in standard terrain-corrected level (Level 1T) with the use 188 of ground control points (GCPs) and necessary elevation data (https://earthexplorer.usgs.gov). The

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ALOS-08 image used here was orthorectified and corrected for atmospheric effects in Salerno et al.
morphologicalal measurements related to ponds and glaciers obtained from remote sensing imagery, maps  level at p <0.05. The normality of the data is tested using the Shapiro-Wilk test (Shapiro and Wilk, 1965;206 Hervé, 2015). The data were also tested for homogeneity of variance with the Levene's test (

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To reconstruct the climatic trends before the 1990s, we compared the annual and seasonal 222 with selected regional gridded and reanalysis datasets (Table SI1). Table 1 shows the coefficient of 223 correlation found for these comparisons. Era Interim (r = 0.92, p<0.001) for mean temperature (Fig. 4a)

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and GPCC (r = 0.92, p<0.001) for precipitation ( Fig. 4b) provide the best performance at the annual level.

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All these comparisons are shown in Figure SI1. We observe that precipitation increased significantly until
230 Furthermore, Table 1 shows the low capability of all the products to correctly simulate monsoon 231 temperatures and in particular the daily maximum ones. Figure SI2a reports these correlations at monthly 232 level, while Figure SI2b highlights the misfit between the temperature trends during the monsoon period. selected, according to the criteria described above, a total of 64 ponds (approximately 1/3) (Fig. 2a). Table   236 2 provides a general summary of their morphological features. We prefer to use the median values to 237 describe these environments because, in general, we observed that these morphological data do not follow

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The observed changes in the surface area of all the considered ponds are listed in Table 3. In general,

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all unconnected ponds in the last fifty years  decreased by approximately 10%, with a 244 significant difference based on the Friedman test (p<0.01). Figure 4d and Table 3 show that, until the The glacier melt related to each glacier within the pond basins has been calculated considering both 290 the both maximum and mean daily temperatures. The averages for all selected cases are analyzed for each 291 season in Figure SI4, which reveals that the only period producing a sensible contribution is the monsoon 292 period if the maximum daily temperatures are considered the main driver of the process. The reason can 293 be easily observed in Figure 2b, which shows the 0 °C isotherms corresponding to the mean and 294 maximum temperatures. Only the 0 °C isotherm related to the daily maximum temperature during the 295 monsoon period is located higher than mean elevation of the analyzed glaciers.
The T-index model only

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calculates the melting associated with temperatures above 0 °C, thereby explaining this pattern. In other 297 words, the diurnal temperatures influence the melting processes much more the nocturnal ones, which are 298 considered in the mean daily temperature. Figure 6b shows that the trend is significantly decreasing (3% 299 yr -1 , p<0.05), according to the decrease observed in maximum temperature.

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As anticipated, the highest correlations between ponds surface areas and potential drivers are found 301 for the monsoon period. Based on Table SI5, we observe that precipitation, maximum monsoon     potential drivers of change (maximum temperature, precipitation, glacier melt, and potential evaporation) 759 related to the monsoon season. Coefficients of correlation are reported in Table SI5. All trends related to 760 ponds and variables are provided in Figure SI1 and SI2.

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Coefficients of correlation are reported in Table SI5. All trends related to ponds and variables are 778 provided in Figure SI1 and SI2.