The main factors contributing to rising seas are the warming of the oceans and the resulting thermal expansion of sea water as well as the melting of land based ice. Both contributions result in spatially not uniform sea-level change patterns that, depending on the region, reinforce or dampen regional sea-level changes. To accurately assess regional rates of changes in sea level it is important to quantify all processes that contribute to regional sea level variability.

Due to gravitational effects, the melting of land-based ice affects different regions differently. While not important for global mean sea level, the location of a shrinking glaciers is critical with respect to where in the worlds ocean sea level is rising or sinking. Important questions to discuss are

a) Glaciers from which region of the world contributed strongest to sea-level change?

b) What are the expectations for the future?

c) Which coastal regions are most affected by by glacial melting?

d) Which glaciated regions have the strongest impacts of populated coastal regions and what governs the uncertainties?

Poster Title:

Melting glaciers and rising sease - why it matters where the ice is melting

The world’s mountain areas often provide disproportionally high runoff to the subjacent lowlands. However, the extent to which the lowlands actually depend on mountain water resources has not been examined so far. We therefore take a new viewpoint to map and quantify for the first time the lowland inhabitants potentially depending on mountain water resources world-wide.

Our analysis is based on the high-resolution Global Hydrological Model PCR-GLOBWB v2.0 (5 arc minutes, ~9 km at the Equator) and spans a timeframe from 1961 to 2050. We incorporate the changing conditions of both runoff and water consumption and can therefore quantify changes in the Anthropocene era as well as make projections for mid-21st century by exploring three SSP-RCP scenarios.

We show that the number of lowland inhabitants critically depending on runoff contributions from mountains is projected to grow from ~0.2 billion (8% of world’s lowland population) in 1961–1970 to ~1.4 B (23%) in 2041–2050 under a ‘middle of the road’ scenario. This growth is mainly due to increased local water consumption in the lowlands and turns out particularly marked in mid-latitude regions of the Northern Hemisphere, which also provide the greatest share of food supply. There, more than one quarter of the region’s lowland population of ~3.1 B is projected to critically depend on mountain runoff contributions by 2041–2050.

Extending our view to food security, we also show that one third of global lowland area equipped for irrigation is currently located in regions that both depend heavily on runoff contributions from mountains and make unsustainable use of local blue water resources. This figure is likely to rise to well over 50% in the coming decades.

In the Tropical Andes, year-round streamflow from glaciers is an important water resource that supports human livelihoods and ecosystems further downstream. However, the advanced shrinking of glaciers, in combination with low adaptive capacity, makes this mountain region among the most vulnerable. A case in point is the vanishing of the second-largest tropical glacier fragment worldwide, in the Vilcanota-Urubamba river basin in southern Peru, which leads to serious implications for local water security.

Other impacts, including degradation of non-glacial water supply and growing water demand, further exacerbate the pressure on socio-environmental systems and water availability, potentially jeopardizing water security on the long term. As a result, the spatiotemporal variability and evolution of both the meltwater propagation through the terrestrial water cycle and its contribution to changing patterns in water availability at the catchment scale are complex, poorly understood, and highly uncertain.

To address this issue, we present a glacier melt vulnerability model that intends to integrate exposure to changing flow regimes, socioeconomic sensitivities, and adaptive capacities related to water efficiency and storage capacities. Our results suggest significant streamflow reductions in headwater areas where human vulnerabilities driven by high levels of poverty and inequality are most pronounced while the majority including hydropower production is situated in the middle basin. Output from the model will be combined with possible future trajectories of glacier shrinkage and main water demand sectors up to 2050.

Adaptation measures to secure future water availability need to take into account the complex interactions and feedbacks between drivers of water supply and demand within an extended upstream-downstream perspective. We identify specific opportunities in the interest of policy makers to implement interventions based on natural infrastructure, which may support robust and adaptive climate change adaptation strategies.