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The impacts of the accelerated glacier retreat in recent decades on glacier runoff changes are still unknown in most Andean catchments, increasing uncertainties in estimating water availability. This particularly affects the outer tropics and Dry Andes, heavily impacted by prolonged droughts. Current global estimates overlook climatic and morphometric disparities, which significantly influence model parameters, among Andean glaciers. Meanwhile, local studies have used different approaches to estimate glacier runoff in a few catchments. Improving 21st-century glacier runoff projections relies on calibrating and validating models using corrected historical climate inputs and calibrated parameters across diverse glaciological zones. Here, we simulate glacier evolution and related runoff changes between the periods 2000–2009 and 2010–2019 across 786 Andean catchments (11 282 km2 of glacierized area, 11° N to 55° S) using the Open Global Glacier Model (OGGM). TerraClimate atmospheric variables were corrected using in situ data, getting a mean temperature bias by up to 2.1 °C and enhanced monthly precipitation. Glacier mass balance and volume were calibrated, where melt factor and the Glen A parameter exhibited significant alignment with varying environmental conditions. Simulation outcomes were validated against in situ data in three documented catchments (with a glacierized area > 8 %) and monitored glaciers. Our results at the Andes scale reveal an average reduction of 8.3 % in glacier volume and a decrease of 2.2 % in surface area between the periods 2000–2009 and 2010–2019. Comparing these two periods, glacier and climate variations have led to a 12 % increase in mean annual glacier melt (86.5 m3s-1) and a decrease in rainfall on glaciers of - 2 % (- 7.6 m3s-1) across the Andes, with both variables comprising the glacier runoff. We confirmed the utility of our corrected regional simulations of glacier runoff contribution at the catchment scale, where our estimations align with previous studies (e.g., Maipo 34° S, Chile) as well as provide new insights on the seasonal glaciers' largest contribution (e.g., La Paz 16° S, Bolivia) and new estimates of glacier runoff contribution (e.g., Baker 47° S, Chile). [ABSTRACT FROM AUTHOR]

River plumes have a direct influence on coastal environments, impacting coastal planktonic and benthic communities, including fishery resources. In general, the main drivers of river plume dynamics are the river discharge and the alongshore wind stress, whereas the tides and topography play a secondary role. In central Chile, rivers flowing into the eastern Pacific have a relatively short path on land, with a high slope and a mixed snow–rain regime. This study aims to understand the interannual variability in the plumes of the Maipo and Rapel rivers in the coastal/shelf area off central Chile and their influence on local ocean dynamics. We used the Coastal and Regional Ocean Community (CROCO) model, with 1 km horizontal resolution and 20 sigma levels, to simulate the ocean dynamics for the period 2003–2011. The results show that the plume's area coverage and coastal ocean salinity are strongly correlated with the river discharges. The predominant northeastward winds control the plumes' orientation toward the northwest. However, episodes of southeastward winds in winter can reverse the plumes' direction, promoting their attachment to the coast and southward transport. Results also show a salification trend linked to the severe droughts hitting central Chile during the studied period. This salification determines a change in local dynamics which could be more frequent in future scenarios of climate change with a significant lack of rain and river discharges along central Chile. [ABSTRACT FROM AUTHOR]

The impacts of the accelerated glacier retreat in recent decades on runoff changes are still unknown in most Andean catchments, thereby increasing uncertainties in estimating and managing water availability. Here, we used a monthly time step to simulate glacier evolution and related runoff changes for 36 % of the glacierized surface area of the Andes (11,282 km2 in 786 catchments, 11° N–55° S) using the Open Global Glacier Model (OGGM) and a corrected and evaluated version of the TerraClimate dataset between 2000 and 2019. The glacier mass balance and volume were calibrated glacier-by-glacier. The simulation results were evaluated with in situ data in three documented catchments and 15 glaciers. Our results show that the glacier volume (−8.3 %) and surface area (−2.2 %) are reduced in 93 % of the catchments between the periods 2000–2009 and 2010–2019. This glacier loss is associated with changes in climate conditions (precipitation = −9 %; temperature = +0.4 ± 0.1 °C) inducing an increase in the mean annual glacier melt of 12 % (86.5 m3/s) and a decrease in the mean annual rainfall on glaciers of −2 % (−7.6 m3/s). We find a regional pattern in the melt factors showing decreasing values from the Tropical Andes toward the Wet Andes. A negative mass balance trend is estimated in the three documented catchments (glacierized surface area > 8 %), showing the largest mean glacier contribution during the transition season (September–November) in La Paz (Bolivia) (45 %) followed by Baker (Chile) (43 %) and Maipo (Chile) (36 %) during the summer season (January–March). In addition, our evaluation in the monitored glaciers indicates an underestimation of the mean simulated mass balance by 185 mm w.e. yr−1 and a high mean correlation (r = 0.7). We conclude that the large increases in the simulated glacier melt in the Dry Andes (36 %) and the Tropical Andes (24 %) have helped to improve our knowledge of the hydro-glaciological characteristics at a much wider scale than previous studies, which focused more on a few select catchments in the Andes. [ABSTRACT FROM AUTHOR]

River plumes have a direct influence on coastal environments, impacting coastal planktonic and benthic communities, including fishery resources. In general, the main drivers of river plume dynamics are the river discharge and the alongshore wind stress, whereas the tides and topography play a secondary role. In the Central parto of Chile, rivers flowing into the eastern Pacific have a relatively short path on the land, with a high slope; further they are characterized by a mixed snow-rain regime. This study aims to understand the interannual variability of the plumes of the Maipo and Rapel rivers in the Coastal/shelf area off Chile and its influence on local ocean dynamics. We used the Coastal and Regional Ocean Community model (CROCO), with 1 km resolution and 20 sigma levels, to simulate the ocean dynamics of the area over the period 2003-2011. The results show that the plume's area coverage and coastal ocean salinity are strongly correlated to the river discharges. The predominant southwestern wind controls the plumes orientation toward northwest; however, episodes of wind changing direction from northwest in winter can reverse the plumes direction, making them squeezed to the coast and moving southward. Results also show, for the decade under evaluation, a salification trend linked to the severe droughts hitting Central Chile during the studied period. This salification determines a change in local dynamics. [ABSTRACT FROM AUTHOR]

River plumes have a direct influence on coastal environments, impacting coastal planktonic and benthic communities, including fishery resources. In general, the main drivers of river plume dynamics are the river discharge and the alongshore wind stress, whereas the tides and topography play a secondary role. In the Central parto of Chile, rivers flowing into the eastern Pacific have a relatively short path on the land, with a high slope; further they are characterized by a mixed snow-rain regime. This study aims to understand the interannual variability of the plumes of the Maipo and Rapel rivers in the Coastal/shelf area off Chile and its influence on local ocean dynamics. We used the Coastal and Regional Ocean Community model (CROCO), with 1 km resolution and 20 sigma levels, to simulate the ocean dynamics of the area over the period 2003–2011. The results show that the plume's area coverage and coastal ocean salinity are strongly correlated to the river discharges. The predominant southwestern wind controls the plumes orientation toward northwest; however, episodes of wind changing direction from northwest in winter can reverse the plumes direction, making them squeezed to the coast and moving southward. Results also show, for the decade under evaluation, a salification trend linked to the severe droughts hitting Central Chile during the studied period. This salification determines a change in local dynamics. [ABSTRACT FROM AUTHOR]

Seasonal snow is a critical component of the surface energy balance and hydrologic cycle, yet global maps of seasonal snow boundaries are not readily available. Snow persistence (SP), the fraction of a year that snow is present on the ground, is an easily globally observed snow metric that can be used to map snow zones globally. Here we map snow zones across the globe using SP calculated from the MODIS10A2 product; evaluate how SP relates to precipitation, temperature, and climate indices; and examine trends in annual SP for 2001–2016. In the Northern Hemisphere, intermittent, seasonal, and permanent snow zones occupy a far greater percent (63%) of the land surface than in the Southern Hemisphere (<5%) where the low snow zone dominates (>95%). SP is most variable from year to year near the snow line, which has a relatively consistent decrease in elevation with increasing latitude across all continents. At lower elevations, SP is typically best correlated with temperature, whereas precipitation has greater relative importance for SP at high elevations. SP is best correlated with the North Atlantic Oscillation in all continents except South America, where the Southern Annular Mode is a stronger influence, and Africa, where the strongest correlation is with the Oceanic Niño Index. Areas with decreasing SP trends cover 5.8% of snow zone areas, whereas those with increasing trends cover 1.0% of this area. The largest areas of declining SP are in the seasonal snow zones of the Northern Hemisphere. Trend patterns vary within individual regions, with elevation, and on windward‐leeward sides of the mountains. This study supplies a framework for comparing snow between regions, highlights areas with snow changes, and can facilitate analyses of why snow changes vary within and between regions. [ABSTRACT FROM AUTHOR]

With climate warming, many regions are experiencing changes in snow accumulation and persistence. These changes are known to affect streamflow volume, but the magnitude of the effect varies between regions. This research evaluates whether variables derived from remotely sensed snow cover can be used to estimate annual streamflow at the small watershed scale across the western U.S., a region with a wide range of climate types. We compared snow cover variables derived from MODIS, snow persistence (SP), and snow season (SS), to more commonly utilized metrics, snow fraction (fraction of precipitation falling as snow, SF), and peak snow water equivalent (SWE). Each variable represents different information about snow, and this comparison assesses similarities and differences between the snow metrics. Next, we evaluated how two snow variables, SP and SWE, related to annual streamflow (Q) for 119 USGS reference watersheds and examined whether these relationships varied for wet/warm (precipitation surplus) and dry/cold (precipitation deficit) watersheds. Results showed high correlations between all snow variables, but the slopes of these relationships differed between climates, with wet/warm watersheds displaying lower SF and higher SWE for the same SP. In dry/cold watersheds, both SP and SNODAS SWE correlated with Q spatially across all watersheds and over time within individual watersheds. We conclude that SP can be used to map spatial patterns of annual streamflow generation in dry/cold parts of the region. Applying this approach to the Upper Colorado River Basin demonstrates that 50% of streamflow comes from areas >3,000 masl. If the relationship between SP and Q is similar in other dry/cold regions, this approach could be used to estimate annual streamflow in ungauged basins. [ABSTRACT FROM AUTHOR]

The Andes span a length of 7000 km and are important for sustaining regional water supplies. Snow variability across this region has not been studied in detail due to sparse and unevenly distributed instrumental climate data. We calculated snow persistence (SP) as the fraction of time with snow cover for each year between 2000 and 2016 from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensors (500 m, 8-day maximum snow cover extent). This analysis is conducted between 8 and 36° S due to high frequency of cloud (>30% of the time) south and north of this range. We ran Mann-Kendall and Theil-Sens analyses to identify areas with significant changes in SP and snowline (the line at lower elevation where SPD20 %). We evaluated how these trends relate to temperature and precipitation from Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) and University of Delaware datasets and climate indices as El Niño-Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Pacific Decadal Oscillation (PDO). Areas north of 29° S have limited snow cover, and few trends in snow persistence were detected. A large area (34 370 km2) with persistent snow cover between 29 and 36° S experienced a significant loss of snow cover (2-5 fewer days of snow year1). Snow loss was more pronounced (62% of the area with significant trends) on the east side of the Andes. We also found a significant increase in the elevation of the snowline at 10-30myear1 south of 29- 30° S. Decreasing SP correlates with decreasing precipitation and increasing temperature, and the magnitudes of these correlations vary with latitude and elevation. ENSO climate indices better predicted SP conditions north of 31° S, whereas the SAM better predicted SP south of 31° S. [ABSTRACT FROM AUTHOR]

ABSTRACT This study develops a method for characterizing snow climatology in the Andes Mountains using the 8-day maximum binary snow cover product from the Moderate Resolution Imaging Spectroradiometer sensor. The objectives are to: (1) identify regions with similar snow patterns and (2) identify snow persistence zones within these regions. Within a study area between 8° and 39°S, snow regions are defined using the (1) minimum elevation of snow cover, (2) rate of change of snow persistence with elevation, and (3) timing of the minimum elevation snow cover. In tropical latitudes (8°-23°S), snow cover is constrained to high elevations (>5000 m), and these areas have steep changes in snow persistence with elevation. Minimal differences in the elevation of snow on the east and west sides of the range suggest that temperature is a primary control on snow presence. Snow cover has minimal seasonal variability in the Tropics between 8° and 14°S, but it peaks in austral fall (March) after the wet season from 14° to 23°S. In mid-latitudes (south of 23°S) snowline decreases in elevation with increasing latitude, and snow persistence changes with elevation are more gradual than in tropical regions. Snow cover peaks in the austral winter throughout the mid-latitudes. Differences in elevations of snow accumulation between the east and west sides of the Andes are greatest between 28° and 37°S, where high mountain peaks produce a strong orographic effect and precipitation shadow. Within the snow regions, four snow zones are defined based on the average fraction of the year that snow persists: (1) little or no snow, (2) intermittent, (3) seasonal, and (4) permanent snow zones. Tropical latitudes have snow cover only on the highest peaks. Areas of seasonal and permanent snow zones are greatest between latitudes 28° and 37°S as a result of higher precipitation than mountains further north and higher elevations than mountains further south. [ABSTRACT FROM AUTHOR]