Glacial lake outburst floods (GLOFs) are a substantial hazard for downstream communities in vulnerable regions, yet unpredictable triggers and remote source locations make GLOF dynamics difficult to measure and quantify. Here, we revisit a destructive GLOF that occurred in Bhutan in 1994 and apply cross-correlation–based seismic analyses to track the evolution of the GLOF remotely (~100 kilometers from the source region). We use the seismic observations along with eyewitness reports and a downstream gauge station to constrain a numerical flood model and then assess geomorphic change and current state of the unstable lakes via satellite imagery. Coherent seismic energy is evident from 1 to 5 hertz beginning approximately 5 hours before the flood impacted Punakha village, which originated at the source lake and advanced down the valley during the GLOF duration. Our analysis highlights potential benefits of using real-time seismic monitoring to improve early warning systems.

Abstract:There is growing evidence that monsoon patterns are changing in the Himalayan region, which could potentially result in loss and damage for local farmers. To understand how farmers adapt to changes in water availability, we conducted a study in Punakha district, Bhutan, using qualitative and quantitative research tools. According to 91% of 273 respondents, water availability for rice irrigation has been decreasing over the last 20 years due to changing rainfall. Most of them have taken measures in response. They may, for example, invest in the maintenance of irrigation channels, develop or modify water-sharing mechanisms, or shift to crops that need less water than rice. Of these farmers, however, 88% indicate that their adaptation measures are insufficient. Moreover, they come with extra costs. We argue that these costs should not only be conceived in monetary terms, but also in terms of time investment, social-cohesion and livelihood security.

The Indian Summer Monsoon (ISM) plays a vital role in the livelihoods and economy of those living on the Indian subcontinent, including the small, mountainous country of Bhutan. The ISM fluctuates over varying temporal scales and its variability is related to many internal and external factors including the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). In 2015, a Super El Niño occurred in the tropical Pacific alongside a positive IOD in the Indian Ocean and was followed in 2016 by a simultaneous La Niña and negative IOD. These events had worldwide repercussions. However, it is unclear how the ISM was affected during this time, both at a regional scale over the whole ISM area and at a local scale over Bhutan. First, an evaluation of data products comparing ERA5 reanalysis, TRMM and GPM satellite, and GPCC precipitation products against weather station measurements from Bhutan, indicated that ERA5 reanalysis was suitable to investigate ISM change in these two years. The reanalysis datasets showed that there was disruption to the ISM during this period, with a late onset of the monsoon in 2015, a shifted monsoon flow in July 2015 and in August 2016, and a late withdrawal in 2016. However, this resulted in neither a monsoon surplus nor a deficit across both years but instead large spatial-temporal variability. It is possible to attribute some of the regional scale changes to the ENSO and IOD events, but the expected impact of a simultaneous ENSO and IOD events are not recognizable. It is likely that 2015/16 monsoon disruption was driven by a combination of factors alongside ENSO and the IOD, including varying boundary conditions, the Pacific Decadal Oscillation, the Atlantic Multi-decadal Oscillation, and more. At a local scale, the intricate topography and orographic processes ongoing within Bhutan further amplified or dampened the already altered ISM.

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<p><strong>Abstract.</strong> The biogeochemistry of mountain forests in the Hindu Kush-Himalaya range is poorly studied although climate change is expected to disproportionally affect the region. We measured the soil CO<sub>2</sub> efflux (Rs) at a high elevation (3260 m) coniferous, and a lower elevation (2460 m) broadleaved forest in Bhutan, eastern Himalayas, during 2014 and 2015. Both sites experienced typical monsoon weather (cold-dry winters, warm-wet summers) during the study. Trenching was applied to estimate the contribution of autotrophic (Ra) and heterotrophic (Rh) soil respiration. The temperature (<i>Q</i><sub>10</sub>) and the moisture sensitivities of Rh were determined under controlled laboratory conditions and were used to model Rh in the field. The higher elevation coniferous forest had a higher standing tree stock, reflected in higher soil C stocks and basal soil respiration (<i>R</i><sub>10</sub>). Rs was similar between the two forests (2015: 14.5 ± 1.2 t C yr<sup>−1</sup> broadleaved; 12.8 ± 1.0 t C yr<sup>−1</sup> coniferous). Modelled annual contribution of Ra was ~ 45 % at both forests with a low autotrophic contribution during winter and high contribution during the monsoon season. Ra, estimated from trenching, was lower and highly variable, indicating that trenching poorly performed at these forests/soils. Rs neatly followed the annual course of soil temperature (field <i>Q</i><sub>10</sub> between 4 and 5) at both sites. Co-variation between soil temperature and moisture likely was the main cause for the high <i>Q</i><sub>10</sub> obtained from field Rs. Temperature sensitivity of Rh was lower (<i>Q</i><sub>10</sub> ~ 2.3 at both sites). Under the preceding weather conditions, a simple temperature-driven model was able to explain more than 90 % of the temporal variation in Rs. To predict and understand how Rs responds to infrequently occurring extreme climate conditions such as monsoon failures, however, longer Rs time series are required for a better integration of interactions between soil temperature, moisture, Ra and Rh.</p>