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Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from such seismic disturbances, depending on how recovery is defined. We examine several proxies of river recovery around Pokhara, Nepal’s second largest city. We use a freshly exhumed cohort of floodplain trees in growth position as a geomorphic marker of rapid sedimentation that formed a fan covering 148 km² in a Lesser Himalayan basin with tens of meters of debris. Radiocarbon dates of these buried trees are consistent with those of nearby valley fills linked to major Himalayan earthquakes during medieval times, and offer benchmarks for estimating average rates of sedimentation and re-incision. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos documenting historic channel changes, estimated removed volumes, calculated long-term denudation rates, and dated re-exhumed tree trunks to reconstruct dated geomorphic marker surfaces. The volumes of sediment lost from these surfaces require net sediment yields of up to 4200 t km–² yr–¹, averaged over some 650 years since the last inferred earthquake. These rates exceed density-adjusted rates of catchment-wide denudation derived from concentrations of cosmogenic ¹⁰Be in river sands. The lithological composition of active channel-bed load differs from that of local bedrock, confirming that rivers are still mainly evacuating medieval valley fills, locally incising at rates of 160 to 220 mm yr–¹ in the past 50 years. Pronounced knickpoints and epigenetic gorges at tributary junctions add to the picture of a protracted fluvial response; only the distal portions of the earthquake-derived sediment wedge have been incised to near their base. Our results challenge the notion that mountain rivers recover from earthquakes within years to decades. The valley fills around Pokhara document that even highly erosive Himalayan rivers need at least centuries to millennia to adjust. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in mountain regions.

The Kathmandu Valley in the Himalayan foothills, considered as one of the global "hot spots" for what concerns air pollution, is currently facing severe air quality problems due to rapid urbanization processes, dramatic land use changes, socioeconomic transformation and high population growth. In this work, we present the first full year (February 2013 - February 2014) analysis of simultaneous measurements of two short-lived climate forcers/pollutants (SLCF/P), i.e. ozone (O3) and equivalent black carbon (BC), and aerosol number concentration at Paknajol (27°43'4'' N, 85°18'32'' E, 1380 m a.s.l.), in the city center of Kathmandu. These observations were carried out in the framework of the SusKat-ABC (A Sustainable Atmosphere for the Kathmandu Valley - Atmospheric Brown Cloud) campaign in Nepal. The diurnal behavior of BC and aerosol number concentration indicated that local pollution sources represent the major contribution to air pollution in this city. In addition to photochemistry, the planetary boundary layer (PBL) dynamic plays an important role in determining O3 variability, as suggested by the analysis of seasonal changes of the diurnal cycles and the correlation with meteorological parameters and aerosol properties. Especially during pre-monsoon, high values of O3 were observed during the afternoon/evening. This could be related to mixing and entrainment processes between upper residual layers and the PBL. During this season, the high O3 appeared well related to the impact of major open vegetation fires occurring in Nepal. On a synoptic-scale perspective, westerly and regional atmospheric circulations appeared to be especially conducive for the occurrence of the high BC and O3 values. The very high values of the SLCF/P, detected during the whole measurement period, indicated persisting adverse air quality conditions, dangerous for the health of over 3 million residents of the Kathmandu Valley, and the environment. Consequently, all of this information may be useful for implementing control measures to mitigate the occurrence of acute pollution levels in the Kathmandu Valley and the surrounding area.

Lumbini, in southern Nepal, is a UNESCO world heritage site of universal value as the birthplace of the Buddha. Poor air quality in Lumbini and surrounding regions is a great concern for public health as well as for preservation, protection and promotion of Buddhist heritage and culture. Measurements of the ambient concentrations of key air pollutants (BC, PM, CO, O3) were conducted in Lumbini, first of its kind in Lumbini, during an intensive measurement period of three months (April-June 2013) in the pre-monsoon season. The measurements were carried out as a part of the international air pollution measurement campaign; SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley - Atmospheric Brown Clouds). Hourly average concentrations were: BC: 4.9±3.8 (0.3-29.9) μg/m3; CO: 344.1±160.3 (124.9-1429.7) ppbv; O3: 46.6±20.3 (0.85-118.1) ppbv; PM10: 128.8±91.9 (10.5-603.9) μg/m3; and PM2.5: 53.1±35.1 (6.1-272.2) μg/m3. These levels are comparable to heavily polluted sites in the region. The 24-h average PM2.5 and PM10 concentrations frequently (94% and 85%, respectively, of the sampled period) exceeded the WHO guideline, which implies significant health risks for the residents and visitors in the region. Clear diurnal cycles were observed for the pollutants. Occurrences of peak concentrations during the study period were due to regional forest fires and meteorological conditions conducive of transport to Lumbini. The WRF-STEM model was used to simulate the meteorology and the pollution concentration, and showed the model concentration to be lower by a factor of ~1.4-5, even though the model was able to capture the observed variability. Regionally tagged CO tracers and the chemical composition of fine mode PM2.5 was obtained from the model. The aerosol spectral light absorption coefficients obtained from Lumbini indicated presence of BC from both biomass burning and fossil fuel combustion, with more than half of the ambient BC attributable to fossil fuel combustion. Given the high pollution levels, there is a clear and urgent need for setting up a network of long-term air quality monitoring stations in the greater Lumbini region. This is a special place which demands special attention to safeguard the valuable world heritage properties as well as public health and agro-ecosystems in the region from impacts of air pollution.

Particulate matter (PM) mass concentrations, seasonal cycles, source sector, and source region contributions in Central Asia (CA) are analyzed for the period April 2008–July 2009 using the Sulfur Transport and dEposition Model (STEM) chemical transport model and modeled meteorology from the Weather Research and Forecasting (WRF) model. Predicted aerosol optical depth (AOD) values (annual mean value 0.2) in CA vary seasonally, with lowest values in the winter. Surface PM2:5 concentrations (annual mean value 10 μgm3/ also exhibit a seasonal cycle, with peak values and largest variability in the spring/summer, and lowest values and variability in the winter (hourly values from 2 to 90 μgm3/. Surface concentrations of black carbon (BC) (mean value 0.1 μgm3/ show peak values in the winter. The simulated values are compared to surface measurements of AOD as well as PM2:5, PM10, BC, and organic carbon (OC) mass concentrations at two regional sites in Kyrgyzstan (Lidar Station Teplokluchenka (LST) and Bishkek). The predicted values of AOD and PM mass concentrations and their seasonal cycles are fairly well captured. The carbonaceous aerosols are underpredicted in winter, and analysis suggests that the winter heating emissions are underestimated in the current inventory. Dust, from sources within and outside CA, is a significant component of the PM mass and drives the seasonal cycles of PM and AOD. On an annual basis, the power and industrial sectors are found to be the most important contributors to the anthropogenic portion of PM2:5. Residential combustion and transportation are shown to be the most important sectors for BC. Biomass burning within and outside the region also contributes to elevated PM and BC concentrations. The analysis of the transport pathways and the variations in particulate matter mass and composition in CA demonstrates that this region is strategically located to characterize regional and intercontinental transport of pollutants. Aerosols at these sites are shown to reflect dust, biomass burning, and anthropogenic sources from Europe; South, East, and Central Asia; and Russia depending on the time period. Simulations for a reference 2030 emission scenario based on pollution abatement measures already committed to in current legislation show that PM2:5 and BC concentrations in the region increase, with BC growing more than PM2:5 on a relative basis. This suggests that both the health impacts and the climate warming associated with these particles may increase over the next decades unless additional control measures are taken. The importance of observations in CA to help characterize the changes that are rapidly taking place in the region are discussed., JRC.H.2-Air and Climate