Abstract. The Heihe River basin in northwest China depends heavilyon both anthropogenic and natural storage (e.g., surface reservoirs, rivers andgroundwater) to support economic and environmental functions. The QilianMountain cryosphere in the upper basin is integral to recharging thesestorage supplies. It is well established that climate warming is drivingmajor shifts in high-elevation water storage through loss of glaciers andpermafrost. However, the impacts on groundwater–surface-water interactionsand water supply in corresponding lower reaches are less clear. We built anintegrated hydrologic model of the middle basin, where most water usageoccurs, in order to explore the hydrologic response to the changingcryosphere. We simulate the watershed response to loss of glaciers (glacier scenario),advanced permafrost degradation (permafrost scenario), both of these changes simultaneously (combined scenario) andprojected temperature increases in the middle basin (warming scenario) by alteringstreamflow inputs to the model to represent cryosphere-melting processes, aswell as by increasing the temperature of the climate forcing data. Netlosses to groundwater storage in the glacier scenario and net gains in the permafrost and combined scenarios showthe potential of groundwater exchanges to mediate streamflow shifts. Theresult of the combined scenario also shows that permafrost degradation has more of animpact on the system than glacial loss. Seasonal differences ingroundwater–surface-water partitioning are also evident. The glacier scenario hasthe highest fraction of groundwater in terms of streamflow in early spring. Thepermafrost and combined scenarios meanwhile have the highest fraction of streamflowinfiltration in late spring and summer. The warming scenario raises the temperatureof the combined scenario by 2 ∘C. This results in net groundwater storageloss, a reversal from the combined scenario. Large seasonal changes inevapotranspiration and stream network connectivity relative to the combined scenario show thepotential for warming to overpower changes resulting from streamflow. Ourresults demonstrate the importance of understanding the entire system ofgroundwater–surface-water exchanges to assess water resources underchanging climatic conditions. Ultimately, this analysis can be used toexamine the cascading impact of climate change in the cryosphere on theresilience of water resources in arid basins downstream of mountain rangesglobally.
more »
« less
Groundwater Buffers Decreasing Glacier Melt in an Andean Watershed—But Not Forever
Accelerating mountain glacier recession in a warming climate threatens the sustainability of mountain water resources. The extent to which groundwater will provide resilience to these water resources is unknown, in part due to a lack of data and poorly understood interactions between groundwater and surface water. Here we address this knowledge gap by linking climate, glaciers, surface water, and groundwater into an integrated model of the Shullcas Watershed, Peru, in the tropical Andes, the region experiencing the most rapid mountain‐glacier retreat on Earth. For a range of climate scenarios, our model projects that glaciers will disappear by 2100. The loss of glacial meltwater will be buffered by relatively consistent groundwater discharge, which only receives minor recharge (~2%) from glacier melt. However, increasing temperature and associated evapotranspiration, alongside potential decreases in precipitation, will decrease groundwater recharge and streamflow, particularly for the RCP 8.5 emission scenario.
more » « less- NSF-PAR ID:
- 10362028
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 46
- Issue:
- 22
- ISSN:
- 0094-8276
- Page Range / eLocation ID:
- p. 13016-13026
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract The importance of glacier meltwater as a source of mountain-block recharge remains poorly quantified, yet it may be essential to the integrity of alpine aquatic ecosystems by maintaining baseflow in streams and perennial flow in springs. We test the hypothesis that meltwater from alpine glaciers is a critical source of recharge for mountain groundwater systems using traditional stable isotopic source-identification techniques combined with a novel application of microbial DNA. We find that not only is alpine glacier meltwater a critical source of water for many springs, but that alpine springs primarily supported by glacial meltwater contain microbial taxa that are unique from springs primarily supported by seasonal recharge. Thus, recharge from glacial meltwater is vital in maintaining flow in alpine springs and it supports their distinct microbiomes.
-
more » « less
Abstract Himalayan lakes represent critical water resources, culturally important waterbodies, and potential hazards. Some of these lakes experience dramatic water-level changes, responding to seasonal monsoon rains and post-monsoonal draining. To address the paucity of direct observations of hydrology in retreating mountain glacial systems, we describe a field program in a series of high altitude lakes in Sagarmatha National Park, adjacent to Ngozumba, the largest glacier in Nepal. In situ observations find extreme (>12 m) seasonal water-level changes in a 60-m deep lateral-moraine-dammed lake (lacking surface outflow), during a 16-month period, equivalent to a 5
$$\times 10^6$$ $$^3$$ -
more » « less
Abstract. Climate models predict amplified warming at high elevations in low latitudes,making tropical glacierized regions some of the most vulnerable hydrologicalsystems in the world. Observations reveal decreasing streamflow due toretreating glaciers in the Andes, which hold 99% of all tropicalglaciers. However, the timescales over which meltwater contributes tostreamflow and the pathways it takes – surface and subsurface – remainuncertain, hindering our ability to predict how shrinking glaciers willimpact water resources. Two major contributors to this uncertainty are thesparsity of hydrologic measurements in tropical glacierized watersheds andthe complication of hydrograph separation where there is year-round glaciermelt. We address these challenges using a multi-method approach that employsrepeat hydrochemical mixing model analysis, hydroclimatic time seriesanalysis, and integrated watershed modeling. Each of these approachesinterrogates distinct timescale relationships among meltwater, groundwater,and stream discharge. Our results challenge the commonly held conceptualmodel that glaciers buffer discharge variability. Instead, in a subhumidwatershed on Volcán Chimborazo, Ecuador, glacier melt drives nearly allthe variability in discharge (Pearson correlation coefficient of 0.89 insimulations), with glaciers contributing a broad range of 20%–60%or wider of discharge, mostly (86%) through surface runoff on hourlytimescales, but also through infiltration that increases annual groundwatercontributions by nearly 20%. We further found that rainfall may enhanceglacier melt contributions to discharge at timescales that complement glaciermelt production, possibly explaining why minimum discharge occurred at thestudy site during warm but dry El Niño conditions, which typicallyheighten melt in the Andes. Our findings caution against extrapolations fromisolated measurements: stream discharge and glacier melt contributions intropical glacierized systems can change substantially at hourly tointerannual timescales, due to climatic variability and surface to subsurfaceflow processes.
-
more » « less
Abstract Global groundwater resources are stressed and the effects of climate change are projected to further disrupt recharge processes. Therefore, we must identify the buffers to climate change in hydrogeologic systems in order to understand which groundwater resources will be disproportionally affected by these changes. Here, we utilize a novel combination of remote sensing (e.g. Landsat) and groundwater residence time data (3H,36Cl) to identify the factors controlling the hydrogeologic stability of aridland mountain-front springs in response to a major climate event, the 2011–2017 California drought. Desert springs within Owens Valley (CA) support unique ecosystems that are surrounded by lush, green vegetation sustained only by discharging groundwater and are not reliant on localized precipitation. Therefore, the health or ecological response of this vegetation is a direct reflection of the hydrogeologic stability of the mountain-block groundwater system since water is the limiting resource for riparian plant growth in arid regions. We compared spring water residence times to vegetation health metrics computed from Landsat imagery leading up to and during the drought interval. We observe that the vegetation surrounding springs discharging a high fraction of modern and bomb-pulse groundwater (<100 years) showed evidence of increased drying and desiccation as the drought progressed. In comparison, springs discharging a higher fraction of old groundwater (>100 years) showed little response thereby supporting the conceptual model where old groundwater, i.e. a distribution of deep and stable groundwater flowpaths, buffers short- to long-term climate perturbations and may provide hydrogeologic resistance to future effects from climate change.
