Glacier recession, debris cover development and the implications for water resources in Afghanistan

Rapid climate change is impacting water resources in Afghanistan, a country in the western Himalayas. It is a semi-arid to arid country of Central Asia where livelihoods and economies have developed to be strongly dependent upon mountain water resources, and where snow and glacier melt deliver 80% of Afghanistan’s water supply. It is also poorly-developed in terms of scientific research and environmental monitoring. Average global temperatures are rising and glaciers are shrinking significantly, potentially impacting water supply to a critical degree. This effect is likely hidden for the time being as glaciers are still larger in volume than that associated with a warmer and warming climate. However, once glaciers shrink to a certain size, “peak water” will be reached. Water supply will decline. If winter snowfall declines, or becomes more variable, glaciers are less likely to compensate for the associated water shortage that results. Recent research has emphasized the complexity of identifying when peak water develops, not least because as glaciers retreat they may develop extensive debris cover, which can significantly modify the relationship between climate change and glacier melt. Given the lack of research in Afghanistan on this topic, the primary aim of this thesis is to quantify the impacts of ongoing and future climate change on Afghan glaciers and the associated consequences for water resources in Afghanistan. To this end, a multidisciplinary approach is used, based on the combination of remote sensing, a restricted field campaign, hydrological modeling, archival data, and locally adjusted climate change scenarios. The PhD thesis addressed the following four research questions: R1: Is it possible to improve remote sensing techniques for glacier monitoring in Afghanistan to allow mapping of not only ice cover but also debris-covered ice at the scale of the entire country? R2: How have the total, bare ice and debris-covered ice extents of Afghanistan glaciers changed in recent decades with the onset of rapid warming? R3: Is it possible to develop a glacier-snow melt runoff model suitable for application over large scales in the data poor context of Afghanistan? R4: How has and how will climate change influence future glacier runoff in Afghanistan? This study is contextualized through a systematic review of more than 130 scientific articles, reports and data sources to assess the potential impacts of climate change on the cryosphere, streamflow, groundwater and hydrological extremes in Afghanistan and to highlight knowledge gaps. This review shows the importance of the cryosphere for Afghan water resources and identifies the need to develop a better inventory of glacier cover in Afghanistan, notably taking into account debris-cover given the geology and geomorphology of the region. To do this, the thesis develops two new debris-cover mapping indices based on thermal and near Infrared Landsat 8 bands. The indices are calibrated with field data, and validation both within and beyond Afghanistan suggests that they have a high level of accuracy. Principal components analysis was applied to 9 glacier parameters to identify the most influential drivers of debris-covered ice extent. This analysis showed that lower proportions of debris cover were associated with glaciers with a higher elevation range that were larger, longer and wider. However, these patterns were statistically clearer when the dataset was broken down into climate zones and geological regions. This methodology is then applied to two timespans (2000-2008 and 2008-2020) to assess recent glacier changes in Afghanistan. Three glacier inventories were developed for the years 2000, 2008, and 2020. In 2020, a glacier area of 2684±100.7 km2 was mapped, split into 75±0.7 % clean ice area and 25±3.0 % debris-covered ice. Total glacier area retreated by -4.5±0.5 km2 yr-1 (-0.15±0.01 % yr-1) between 2000 and 2008 and -12.3±1.5 km2 yr-1 (-0.43±0.05 % yr-1) between 2008 and 2020. However, the analysis revealed substantial spatial variation in these retreat rates based upon geographical region, glacier size and climate region. The results point to the environmental complexity of Afghanistan and suggest that certain regions may pass through peak water much sooner than others. Debris cover changes were also found to be complex, with debris-covered ice extent increasing much more for smaller glaciers <2.5 km2 than larger ones. In order to understand the implications of glacier recession now and in the future for Afghan water resources, three representative catchments were selected based on their locations and data availability, the Taqchakhana catchment (264.4 km2 area with 2.8% glacier cover) in the north; the Sust catchment (4609 km2 area with 15.6% glacier cover) in the east; and the Bamyan catchment (325.3 km2 area with 0.7% glacier cover) in the center of Afghanistan. Current glacier retreat rates are different for each catchment on the basis of the glacier change study. These were also catchments with climate and streamflow data from 2012 to 2019 provided by the Ministry of Energy and Water of Afghanistan. To understand the current and future relative contributions of ice, snow and other components to water supply, Hydrobricks, a new semi-lumped, glacio-hydrological modeling framework based on a C++ core with a Python interface, was used. The model was modified to allow a simple representation of the effects of debris cover development on ice melt. The model was individually calibrated for each catchment based on Shuffled Complex Evolution Algorithm (SCE-UA), with the best parameters taken after 30,000 iterations. Eight regional climate models (RCMs) under two scenarios (2.6 and 8.5) were used in the model to simulate future streamflow in the catchments. The RCMs were bias-corrected using non-parametric statistical transformation. Future glacier evolution was introduced to the model using a very simple propagation of current measured glacier recession rates into the future. Validation of the calibrated model produced good values of the Kling-Gupta efficiency (KGE) for simulated daily streamflow (KGE >⁓0.8). Glacier runoff dominated the Sust catchment (76%); rain and snow runoff the Taqchakhana catchment (50%) and baseflow the Bamyan catchment (61%). Projected streamflow under RCP 2.6 suggests that mean annual glacier runoff for the Sust and Taqchakhana catchments will increase until 2050, following an increase in temperature (0.9 ˚C). Then runoff declines to the end of the 21st century. The Bamyan is predicted to have declining runoff throughout the 21st century. However, under RCP 8.5 glacier runoff increases more markedly in the Sust and Taqchakhana catchments as temperature rises are larger, climate change mitigation measures do not reverse them. These catchments are likely to pass through a phase of peak water not due to temperature limitation on runoff as under RCP 2.6, but due to progressively diminishing glacier size

Glacier retreat and debris cover evolution in the Afghan Hindu Kush Himalaya between 2000 and 2020

Glaciers play a crucial role in the hydrological cycle, providing water in summer when it is most needed for irrigation. Global warming is leading to glacier retreat and enhanced summer runoff in the short-term, which should occur until glaciers become small enough that there is an end to this glacial subsidy and a reduction of summer runoff. However, debris accumulation, as it may alter the surface energy balance, will modify the rate at which this happens and may represent an important negative feedback. For this reason, quantifying and explaining glacier change in the Hindu Kush Himalaya (HKH) region, notably its relation to changing debris cover, is of paramount importance, especially for a country like Afghanistan with water resources highly dependent on glacial meltwater. This study assessed changes in glaciers of Afghanistan using data for 2000, 2007, 2017 and 2020 based upon the analysis of country-wide Landsat data and innovative indices for mapping both ice and debris-covered glacier extent. Results showed 2862.5±47.8 km2 of total glacier area in the year 2000, decreasing by 45.9 km2to 2007 (i.e. 6.55 km2 per year), by a further 112.0 km2 by 2017 (i.e. 11.2 km2 per year), and by a further 73 km2 (i.e. 24.3 km2 per year) by 2020; that is there is a progressive increase in retreat rates. Of the 231.2 km2 (8.07 %) loss of glacier surface area between 2000 and 2020, almost 81% related to glaciers with a size ≤ 2.01 km2, which accounted for 50% of the total glacier area in the year 2000. Decreases were more dominant in center and northern regions of the country, whilst the northeastern region, the most glaciated part of the country, showed lesser changes. Increases in total debris cover area were found in the northeastern region of the country where there were lower decreases in total glacier area, whilst there were noticeable decreases in total debris cover area observed in southern and southeastern regionss and higher decreases in total glacier area. This suggested that the ability of the glaciers to produce debris cover has regional significance in explaining whether glacier loss occurs. Ice elevation significantly changed over the time; changes in minimum ice elevations were up to +53 m, higher in the north, south, and southeastern regions. Maximum ice elevations decreased by -88 m, suggesting loss of accumulation zones. However, the northeastern part had a positive increase in maximum accumulation zone heights +23 m, this indicates possibility of increases in accumulation area. These results revealed differences in the regional response of Afghan glaciers to climate change. In the next stage of this work, we will link the spatial distributions of glacier response to downstream populations to identify those regions most exposed to the effects of these climate changes

Ice cover loss and debris cover evolution in the Afghanistan Hindu Kush Himalaya between 2000 and 2020

Glaciers in Afghanistan are crucial elements for water resource and summer river flows. They are also threatened by rapid climate warming. This study presents an up-to-date assessment of ice cover loss for the entire country over two periods, 2000–2008 and 2008–2020, using newly developed remote sensing indices that include a more reliable determination of changing debris cover. The results suggest an estimated ice-covered area of 2,690.7 ± 108.2 km2 in 2020, that was 75 ± 0.7% clean ice and 25 ± 3.0 percent debris-covered ice. Total ice-covered area retreated by −0.16 ± 0.01 percent yr−1 between 2000 and 2008 and −0.46 ± 0.05 percent yr−1 between 2008 and 2020. Notably, 60 percent of ice cover loss (2000–2020) related to ice cover extents with a size ≤ 2.5 km2, comprising 60 percent of the total ice-covered area in 2000. Higher altitude accumulation zones also exhibited mass loss. However, there was also substantial spatial variation in these rates of loss based on geographical region, glacier size, and climate zones. In the north-eastern regions that are geographically close to or part of the north-west Karakoram ice cover was declining at a substantially lower rate, stable, or even increasing slightly, as compared with the northern and central regions of Afghanistan

Flood Modeling and Simulation using iRIC: A Case Study of Kabul City

In Afghanistan, floods are common and measures must be taken to protect people and property from damage. There is, however, a lack of detailed observations and research on this subject in this area. Therefore, flood simulation models are needed to identify flood-prone areas. In this study, International River Interface Cooperative (iRIC) program that is river flow and riverbed variation analysis software with several solvers has been used. Nays2DFlood solver that simulates 2dimenstional plane flow has applied to a past flood in Kabul city. River discharge from two inflow points and averaged precipitation from three rain gauges at the time of flooding given as input to the model including DEM (Digital Elevation Model) data. The iRIC was confirmed as a 90-m grid digital elevation model to determine the position of streamlines correctly. However, the highest flood depth was overestimated because the 90-m grids were too coarse to detect the slight slope of the riverbed in some areas. Then the elevation of the riverbed modified using data acquired from Google Earth, and the simulation results improved. Moreover, it was found that river water rather than rainfall was the main cause of the flooding

Flood Modeling and Simulation using iRIC: A Case Study of Kabul City

In Afghanistan, floods are common and measures must be taken to protect people and property from damage. There is, however, a lack of detailed observations and research on this subject in this area. Therefore, flood simulation models are needed to identify flood-prone areas. In this study, International River Interface Cooperative (iRIC) program that is river flow and riverbed variation analysis software with several solvers has been used. Nays2DFlood solver that simulates 2dimenstional plane flow has applied to a past flood in Kabul city. River discharge from two inflow points and averaged precipitation from three rain gauges at the time of flooding given as input to the model including DEM (Digital Elevation Model) data. The iRIC was confirmed as a 90-m grid digital elevation model to determine the position of streamlines correctly. However, the highest flood depth was overestimated because the 90-m grids were too coarse to detect the slight slope of the riverbed in some areas. Then the elevation of the riverbed modified using data acquired from Google Earth, and the simulation results improved. Moreover, it was found that river water rather than rainfall was the main cause of the flooding