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Millions of people rely on river water originating from snow- and ice-melt from basins in the Hindukush-Karakoram-Himalayas (HKH). One such basin is the Upper Indus Basin (UIB), where the snow- and ice-melt contribution can be more than 80%. Being the origin of some of the world's largest alpine glaciers, this basin could be highly susceptible to global warming and climate change. Field observations and geodetic measurements suggest that in the Karakoram Mountains, glaciers are either stable or have expanded since 1990, in sharp contrast to glacier retreats that are prevalently observed in the Himalayas and adjoining high-altitude terrains of Central Asia. Decreased summer temperature and discharge in the rivers originating from this region are cited as supporting evidence for this somewhat anomalous phenomenon. This study used remote sensing data during the summer months (July–September) for the period 2000 to 2017. Equilibrium line altitudes (ELAs) for July, August and September have been estimated. ELA trends for July and September were found statistically insignificant. The August ELA declined by 128 m during 2000–2017 at a rate of 7.1 m/year, testifying to the Karakoram Anomaly concomitant with stable to mass gaining glaciers in the Hunza Basin (western Karakoram). Stable glaciers may store fresh water for longer and provide sustainable river water flows in the near to far future. However, these glaciers are also causing low flows of the river during summer months. The Tarbela reservoir reached three times its lowest storage level during June 2019, and it was argued this was due to the low melt of glaciers in the Karakoram region. Therefore, using remote sensing data to monitor the glaciers' health concomitant with sustainable water resources development and management in the HKH region is urgently needed. [ABSTRACT FROM AUTHOR]

Precipitation elasticity provides a basic estimate of the sensitivity of long-term streamflow to changes in long-term precipitation, and it is especially useful as the first assessment of climate change impact in land and water resource projects. This study estimated and compared the precipitation elasticity (εp) of streamflow in 86 catchments within Pakistan over 50 major rivers using three widely used analytical models: bivariate nonparametric (NP) estimator, multivariate NP analysis, and multivariate double logarithm (DL) model. All the three models gave similar values of elasticity in the range of 0.1–3.5 for over 70–75% of the catchments. This signifies that a 1% change in the annual mean precipitation compared to the long-term historic mean annual precipitation will amplify the streamflow by 0.1–3.5%. In addition, the results suggested that elasticity estimation of streamflow sensitivity using the multivariate DL model is more reliable and realistic. Precipitation elasticity of streamflow is observed high at altitudes ranging between 250 m and 1000 m while the longitudinal and latitudinal pattern of εp shows higher values in the range of 70–75 and 32–36 decimal degrees, respectively. The εp values were found to have a direct relationship with the mean annual precipitation and an inverse relationship with the catchment areas. Likewise, high εp values were noticed in areas where the mean annual temperature ranges between 15 and 24 °C. [ABSTRACT FROM AUTHOR]

Seasonal and annual water supplies of the rivers originating in the Hindukush-Karakoram-Himalaya (HKH) region of Pakistan are important to manage the Indus basin irrigation system for better agricultural production and its dependent agrarian economy. In this study, we simulated the current and future snowmelt runoff in a poorly gauged river basin of the Hindukush region under Representative Concentration Pathways (RCP) climate change scenarios. Snowmelt Runoff Model (SRM) furnished with satellite snow cover maps and hydro-meteorological data were used to simulate the daily river discharge for the period 2000‒2005. The results indicated that SRM has effectually simulated the runoff in Chitral River with Nash-Sutcliffe model efficiency coefficient of 0.85 (0.84) and 0.88 (0.83) in the basin-wide (zone-wise) application during the calibration and validation periods, respectively. The results obtained under future climate change scenario showed ∼14‒19% increase in mean summer discharge under three mid-21st century RCP (2.6, 4.5 and 8.5) scenarios. While an increase of ∼13‒37% is expected under late-21st century RCP scenarios. This study can help water resource managers to plan and manage peak discharges from the Chitral River Basin in the future and can thus prevent major losses due to floods in the area. [ABSTRACT FROM AUTHOR]

This study explores the relative changes and future projections of temperature and precipitation for baseline (1976–2005) and future (2006–2040, 2041–2070, and 2071–2100) periods for the Bajaur, Mohmand, and Khyber districts of Pakistan situated in the Hindu Kush region. Data from 14 GCMs (out of which five GCMs were selected based on evaluation and validation) and three RCMs were downscaled and bias corrected using the quantile delta mapping (QDM) method for GCMs and the best easy systemic (BES) method for RCMs. The future extremes were projected by using the standard indices from the Expert Team on Climate Change Detection and Indices (ETCCDI). Uncertainty in the data was analysed by a probabilistic distribution function (PDF), boxplots, and standard deviation. For RCP4.5, the GCM and RCM projections show an increase in the average maximum temperature of 0.98 °C for 2006–2040, 1.89 °C and 2.04 °C for 2041–2070, and 2.25 °C and 2.56 °C for 2071–2100, respectively, while the increase is almost double for RCP8.5 during the last period (2071–2099) over the whole study area. The percent increase in precipitation over the whole study area from GCMs and RCMs for RCP4.5 is 10.00–17.00% and 21.14–34.47%, while for RCP8.5, it is 11.73–22.12% and 16.17–31.50%, respectively. In RCM projections for RCP4.5, the Khyber district will experience drier conditions in mid-century, while for GCMs (RCP4.5), the same conditions are projected through the end of the century. In terms of extreme events, warm temperature extremes and extreme precipitation events show an increasing trend accompanied by a decrease in cold extremes over all regions. Hence, it is concluded that warm and wet conditions are projected to prevail in all regions. However, GCM data depict less uncertainty compared with RCM data, and while models show less error for the baseline period, the error increases slightly for the future periods. Thus, this study provides research findings along with policy recommendations essential to combat the potential impacts of projected changes in the regional climate. [ABSTRACT FROM AUTHOR]

Satellite-geodetic altimetry investigations in the Karakoram have indicated slight mass gain or loss of the glaciers during the early part of 21st century. Equivalent discharge in the upper Indus Basin due to these mass changes has been estimated at 5 to 10% of mean annual flow. However, satellite altimetry and geodetic glacier mass estimates in the extreme topography of the Karakoram have not yet been counter-validated by hydrological analysis. Therefore, we present a first cross validation of three to five decades of river flow data from the three major watersheds in the Karakoram, with matching series of monthly precipitation, temperature, and evaporation provided by six atmospheric reanalysis products for 1979-2014. The analyses suggest that in most cases river flows have been increasing steadily from the end of the 1960s and 1970s to the middle of the 1990s and have stabilized or are in decline since then. Hunza watershed in Karakoram West shows consistently declining flows over the first half of the analysis period and stable flows during the second half for most of the summer melting season, suggesting mass accumulation. Rising river flows in the Shyok and Shigar watersheds, followed by stabilizing or slightly declining flows from 1995 onward, can be explained by consistently increasing precipitation during the first half of the analysis period, and successive stabilization or minor decline thereof. Flow data do not necessarily suggest considerable loss or gain of glacial mass in the Karakoram during the late 90s and early 2000s as suggested by satellite-based altimetry studies. [ABSTRACT FROM AUTHOR]

Field observations and geodetic measurements suggest that in the Karakoram Mountains, glaciers are either stable or have expanded since 1990, in sharp contrast to glacier retreats that are prevalently observed in the Himalayas and adjoining high-altitude terrains of central Asia. Decreased discharge in the rivers originating from this region is cited as a supporting evidence for this somewhat anomalous phenomenon. Here, we show that river discharge during the melting season of the glaciers in the eastern and western Karakoram, respectively, exhibits rising and falling trends. We have implemented a statistical procedure involving non-parametric tests combined with a benchmark smoothing technique that has proven to be a powerful method for separating the stochastic component from the trend component in a time series. Precipitation patterns determined from ERA-40 and GPCP data indicate that summer-monsoonal precipitation has increased over the Karakoram Mountains in recent decades. Increasing flows in June and July in the eastern Karakoram are due to an increase in summer-monsoonal precipitation. The rising trend of August discharge is due to an increase in the loss of glacier storage at an approximate average rate of 0.186–0.217 mm d-1year-1during the period 1973–2010. Moreover, this rate is higher than the rate of increase in monsoonal snowfall during the months of August and September. Therefore, most plausibly, glacier mass balance in the eastern Karakoram is negative. In the western Karakoram, river flows show declining trends for all summer months for the period 1966–2010, corresponding to a rate of increase of glacier storage by approximately 0.552–0.644 mm d-1year-1, which is also higher than the rate of increase in summer-monsoonal precipitation. The gain of the cryospheric mass in the western Karakoram is in the form of increased thickness of the glaciers and perennial snowpacks instead of areal expansion. This investigation shows two contrasting patterns of trends of river flows that signify both negative and positive mass balance of the Karakoram glaciers. Trends of river flows are spatially and temporally integrated responses of a watershed to changing climate and thereby are important signals of the conditions of the cryospheric component of a watershed where it is highly significant. However, they cannot unequivocally provide indications of the state and fate of the glaciers in the complex hydrometeorological setting of the Karakoram. Extreme caution and care must be exercised in interpreting trends of river discharge in conjunction with climatic data. [ABSTRACT FROM AUTHOR]

Summary The hydrograph separation method, previously proposed to quantify base flow, seasonal snowmelt, and glacial melt components in river flows within Upper Indus basin underestimates glacial melt component. This is particularly limiting for highly glacierized watersheds. The limitation has been corrected by a further refinement of the method. The results with the refined procedure are highly consistent with the physical characteristics such as hypsometry and glacier extents of the watershed even though the method itself is completely independent of the physical characteristics of the watershed where it is applied. Glacial melt far outweigh snowmelt in the rivers draining the Karakoram and Zanskar ranges. In the Karakoram, on an annualized basis, glacial melt proportion varies from 43% to 50% whereas snowmelt varies from 27% to 31%. On the other hand, snowmelt dominates over glacial melt in the rivers draining the western Greater Himalayas and the Hindu Kush. Here snowmelt percentage in river discharge varies from 31% to 53% whereas that of glacial melt ranges from 16% to 30%. In the main stem of Upper Indus River, snowmelt fraction in most cases is slightly greater than the glacial melt fraction. In the main stem, snowmelt percentage ranges from 35% to 44% whereas glacial melt percentage ranges from 25% to 36%. Upper Indus River just upstream of Tarbela Reservoir carries annual flows constituted of 70% melt water of which 26% is contributed by glacial melts and 44% by snowmelts. We also show that during the later part of twentieth century and continuing into the early part of twenty first century glacial melt contributions to river discharge has decreased compared to the previous decades. This phenomenon can be ascribed to either basin wide loss of glacial mass in the recent decades in the elevation range from where most of the glacial melt originates or glacier growth and stability due to either reduction in energy inputs or increase in precipitation or both at the high altitude bands wherefrom glacial melt water originates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Summer river flows in central Karakoram conspicuously exhibit rising trends. [•] Rate of loss of glacial storage is approximately 0.04–0.05mm/day/year. [•] Increasing summer precipitation is responsible for nonnegative glacial mass balance. [•] Rising river flows accompany nonnegative glacial mass balance in central Karakoram. [ABSTRACT FROM AUTHOR]

Highlights: [•] Glacio-hydrometeorological conditions with four flow regimes in Upper Indus Basin. [•] Highest flow regime from July to September carry 53–62% annual flow volumes (m3). [•] Three most glaciated watersheds contribute 48–54% flow to the highest flow regime. [•] Melt water from altitude >3500m constitutes 41–54% of annual flow volumes. [•] Near the outlet, glacial and snow melt components respectively constitute 21% and 49% of annual flows. [Copyright &y& Elsevier]

The Indus Basin, home to approximately 300-million people, has a total area of 1.12 million km2 (47 % Pakistan, 39 % India, 6 % Afghanistan, and 8 % China) and the highest density of irrigated land in the world. The region's rapid population and economic growth in recent decades is expected to continue in the next decades leading to growing demands for water, energy and food. With no abundant surface water left in the basin for future expansion and accelerating use of groundwater, long-term strategic and integrated management of water and its interlinked sectors (the so called water-energy-land nexus) is fundamental for the sustainable development of the region. We developed the NExus Solutions Tool (NEST), an open source computing framework that links an engineering-economic model, representing investment and allocation decisions up to 2050 across water, energy and land-use sectors, to a hydrological model, representing the detailed biophysical processes at high spatial and temporal resolutions. We provide insights into (1) the vulnerability of surface water and groundwater resources to future socioeconomic and climatic change; and (2) how policies, technological solutions and investments can improve the sustainability of water, energy and land transformation pathways while avoiding unintended side effects and minimizing trade-offs among sectors. Initial results show very different optimal investment portfolios for each country in the basin, due to the different strategic access to the main river flows. Stability of policies (such as the Indus Water Treaty) will be important, and new investments (especially in renewable energy, water distribution and water treatment technologies) will be required for achieving sustainable development goals in the water, energy, and food sectors. This study also highlights, under different socio-economic and climate scenarios, which provinces and regions might be mostly exposed to water and food scarcity, and what investments are required to adapt to future challenges. [ABSTRACT FROM AUTHOR]