Km3 Yr Research Articles

Sustained greening of the Antarctic Peninsula observed from satellites

The Antarctic Peninsula has experienced considerable anthropogenic warming in recent decades. While cryospheric responses are well defined, the responses of moss-dominated terrestrial ecosystems have not been quantified. Analysis of Landsat archives (1986–2021) using a Google Earth Engine cloud-processing workflow suggest widespread greening across the Antarctic Peninsula. The area of likely vegetation cover increased from 0.863 km2 in 1986 to 11.947 km2 in 2021, with an accelerated rate of change in recent years (2016–2021: 0.424 km2 yr−1) relative to the study period (1986–2021: 0.317 km2 yr−1). This trend echoes a wider pattern of greening in cold-climate ecosystems in response to recent warming, suggesting future widespread changes in the Antarctic Peninsula’s terrestrial ecosystems and their long-term functioning.

Upwind moisture supply increases risk to water security

Transboundary assessments of water security typically adopt an ‘upstream’ perspective, focusing on hazards and vulnerabilities occurring within a given hydrological basin. However, as the moisture that provides precipitation in the hydrological basin probably originates ‘upwind’, hazards and vulnerabilities potentially altering the moisture supply can be overlooked. Here we perform a global assessment of risk to water security in 379 hydrological basins accounting for upwind vulnerabilities and hazards from limited governance and environmental performance. We compare this upwind assessment with the more conventional approach focusing upstream. We find that accounting for upwind moisture supply increases the assessed risk to water security. The upwind perspective results in 32,900 km3 yr−1 of water requirements (that is, the specific water needs of vegetation for their development) under very high risk, compared with 20,500 km3 yr−1 under the upstream perspective. This study pinpoints the need to account for upwind moisture dependencies in global water-related risk assessments.

Accelerating Glacier Area Loss Across the Andes Since the Little Ice Age

AbstractAndean glaciers are losing mass rapidly but a centennial‐scale context to those rates is lacking. Here we show the extent of >5,500 glaciers during the Little Ice Age chronozone (LIA; c. 1,400 to c. 1,850) and compute an overall area change of −25% from then to year 2000 at an average rate of −36.5 km2 yr−1 or −0.11% yr−1. Glaciers in the Tropical Andes (Peru, Bolivia) have depleted the most; median −56% of LIA area, and the fastest; median −0.16% yr−1. Up to 10 × acceleration in glacier area loss has occurred in Tropical mountain sub‐regions comparing LIA to 2,000 rates to post‐2000 rates. Regional climate controls inter‐regional variability, whereas local factors affect intra‐region glacier response time. Analyzing glacier area change by river basins and by protected areas leads us to suggest that conservation and environmental management strategies should be re‐visited as proglacial areas expand.

The dissolution of olivine added to soil at 32°C: the fate of weathering products and its implications for enhanced weathering at different temperatures

The amendment of agricultural soils by crushed silicate minerals has been proposed to enhance weathering rates and facilitate carbon dioxide (CO2) removal from the atmosphere. Laboratory dissolution experiments typically provide weathering rates that are significantly higher than those observed under natural conditions, while field studies are limited in the nature of data they can collect. This study uses an experimental setup that aims to emulate natural field conditions in a controlled setting using soil cores retrieved from UK cropland amended with crushed olivine at 32°C. Results are compared to enhanced weathering experiments run at 4°C and 19°C under otherwise identical conditions. The data reveal temperature-dependent variations in the behaviour of different elements, most importantly Mg and Si, with silicon being retained at moderate temperatures and magnesium being retained at higher temperatures. These patterns are most likely due to different retention mechanisms, notably Si reprecipitation (e.g. as cation-depleted Si-enriched mineral surface coatings) and cation exchange (affecting Mg, but to a lesser degree Si), such that the influence of cation exchange should be accounted for when interpreting enhanced weathering field data. We therefore recommend that estimates of carbon sequestration should not be based on the behaviour of individual elements. A temperature effect on the weathering rate of olivine added to soil columns is observed with the weathering rate being higher at 32°C than at 19°C and 4°C, and significantly lower than laboratory experiment-derived weathering rates. This further emphasises the need for enhanced weathering field trials, as simple laboratory-derived rates cannot be used to assess the feasibility of enhanced weathering measures. The carbon dioxide capture potential at 32°C is conservatively estimated at ~115 t CO2 km-2 yr-1 assuming an olivine amendment rate of 12.7 kg m-2. Our data suggests that soil accumulation of heavy metals like Cu and Cr at high temperatures (hence high weathering rates) is non-dangerous, however, Ni concentrations in the effluent solution are close to EU guidelines while Cr and Cu are considerably lower than guidelines. All of these conclusions have implications for the application of enhanced weathering for carbon dioxide removal from the atmosphere.

Global patterns in river water storage dependent on residence time

Accurate assessment of global river flows and stores is critical for informing water management practices, but current estimates of global river flows exhibit substantial spread and estimates of river stores remain sparse. Estimates of river flows and stores are hampered by uncertainties in land runoff, an unobserved quantity that provides water input to rivers. Here we leverage global river flow observations and an ensemble of land surface models to generate a globally gauge-corrected monthly river flow and storage dataset. We estimate a global river storage mean (± monthly variability) of 2,246 ± 505 km3 and a global continental flow of 37,411 ± 7,816 km3 yr−1. Our global river water storage time series demonstrates that flow wave residence time is a fundamental driver that can double or halve river water stores and their variability. We also reconcile the wide range in previous estimates of monthly variability in global river flows. We identify previously underappreciated freshwater sources to the ocean from the Maritime Continent (Indonesia, Malaysia and Papua New Guinea) amounting to 1.6 times the Congo River and illustrate our capability of detecting severe anthropogenic water withdrawals.

A Greenland-wide empirical reconstruction of paleo ice sheet retreat informed by ice extent markers: PaleoGrIS version 1.0

Abstract. The Greenland Ice Sheet is a large contributor to global sea level rise, and current mass losses are projected to accelerate. However, model projections of future ice sheet evolution are limited by the fact that the ice sheet is not in equilibrium with present-day climate but is still adjusting to past changes that occurred over thousands of years. While the influence of such committed adjustments on future ice sheet evolution remains unquantified, it could be addressed by calibrating numerical ice sheet models over larger timescales and, importantly, against empirical data on ice margin positions. To enable such paleo data–model interactions, we need Greenland-wide empirical reconstructions of past ice sheet extent that combine geomorphological and geochronological evidence. Despite an increasing number of field studies producing new chronologies, such a reconstruction is currently lacking in Greenland. Furthermore, a time slice reconstruction can help to (i) answer open questions regarding the rate and pattern of ice margin evolution in Greenland since the glacial maximum, (ii) develop a standardised record of empirical data, and (iii) identify new sites for future field campaigns. Based on these motivations, we here present PaleoGrIS 1.0, a new Greenland-wide isochrone reconstruction of ice sheet extent evolution through the Late Glacial and early- to mid-Holocene informed by both geomorphological and geochronological markers. Our isochrones have a temporal resolution of 500 years and span ∼ 7.5 kyr from approximately 14 to 6.5 kyr BP. We describe the resulting reconstruction of the shrinking ice sheet and conduct a series of ice-sheet-wide and regional analyses to quantify retreat rates, areal extent change, and their variability across space and time. During the Late Glacial and early- to mid-Holocene, we find the Greenland Ice Sheet has lost about one-third of its areal extent (0.89 million km2). Between ∼ 14 and ∼ 8.5 kyr BP, it experienced a near-constant rate of areal extent loss of 170 ± 27 km2 yr−1. We find that the ice-sheet-scale pattern of margin retreat is well correlated to atmospheric and oceanic temperature variations, which implies a high sensitivity of the ice sheet to deglacial warming. However, during the Holocene, we observe inertia in the ice sheet system that likely caused a centennial- to millennial-scale time lag in ice extent response. At the regional scale, we observe highly heterogeneous deglacial responses in ice extent evident in both the magnitude and rate of retreat. We hypothesise that non-climatic factors, such as the asymmetrical nature of continental shelves and onshore bed topographies, play important roles in determining the regional- to valley-scale dynamics. PaleoGrIS 1.0 is an open-access database designed to be used by both the empirical and numerical modelling communities. It should prove a useful basis for improved future versions of the reconstruction when new geomorphological and geochronological data become available.

Decadal evolution of fluvial islands and its controlling factors along the lower Yangtze River

Fluvial islands are vital from both morphological and ecological perspectives and consequently have been hotspots of morphodynamic research in large rivers around the world. This study selected 14 representative fluvial islands in the lower reaches of the Yangtze River and explored their spatial-temporal evolution, including their shape and area dynamics during 1945–2016, by interpreting remote sensing images and analyzing the hydrological data. Results indicated that the total area of the 14 fluvial islands showed a growing trend at an average rate of 0.30 km2 yr−1 during the 72 years. The island Fenghuangzhou experienced the largest change in area, while Xiaohuangzhou (XHZ) had the smallest change in area. Sediment discharge and flooding were assumed to be the primary natural factors controlling the island dynamics. Furthermore, dam construction and bank reinforcement also played a critical role in preventing shoreline collapse, improving channel conditions, and promoting the stability of fluvial islands. From 1976 to 2016, the maximum erosion occurred on the left XHZ, while the maximum accretion was found on the Qingjiezhou island. Almost the entire river section experienced an accretion process on the right bank, which was assumed to be caused by the construction of erosion control structures. Besides, the dynamics of the fluvial islands along the lower Yangtze River appears to follow the erosion processes of the river bank. Our findings can provide an important reference for sustainable utilization and management of fluvial islands.

Global datasets of hourly carbon and water fluxes simulated using a satellite-based process model with dynamic parameterizations

Abstract. Diagnostic terrestrial biosphere models (TBMs) forced by remote sensing observations have been a principal tool for providing benchmarks on global gross primary productivity (GPP) and evapotranspiration (ET). However, these models often estimate GPP and ET at coarse daily or monthly steps, hindering analysis of ecosystem dynamics at the diurnal (hourly) scales, and prescribe some essential parameters (i.e., the Ball–Berry slope (m) and the maximum carboxylation rate at 25 °C (Vcmax25)) as constant, inducing uncertainties in the estimates of GPP and ET. In this study, we present hourly estimations of global GPP and ET datasets at a 0.25° resolution from 2001 to 2020 simulated with a widely used diagnostic TBM – the Biosphere–atmosphere Exchange Process Simulator (BEPS). We employed eddy covariance observations and machine learning approaches to derive and upscale the seasonally varied m and Vcmax25 for carbon and water fluxes. The estimated hourly GPP and ET are validated against flux observations, remote sensing, and machine learning-based estimates across multiple spatial and temporal scales. The correlation coefficients (R2) and slopes between hourly tower-measured and modeled fluxes are R2=0.83, regression slope =0.92 for GPP, and R2=0.72, regression slope =1.04 for ET. At the global scale, we estimated a global mean GPP of 137.78±3.22 Pg C yr−1 (mean ± 1 SD) with a positive trend of 0.53 Pg C yr−2 (p<0.001), and an ET of 89.03±0.82×103 km3 yr−1 with a slight positive trend of 0.10×103 km3 yr−2 (p<0.001) from 2001 to 2020. The spatial pattern of our estimates agrees well with other products, with R2=0.77–0.85 and R2=0.74–0.90 for GPP and ET, respectively. Overall, this new global hourly dataset serves as a “handshake” among process-based models, remote sensing, and the eddy covariance flux network, providing a reliable long-term estimate of global GPP and ET with diurnal patterns and facilitating studies related to ecosystem functional properties, global carbon, and water cycles. The hourly GPP and ET estimates are available at https://doi.org/10.57760/sciencedb.ecodb.00163 (Leng et al., 2023a) and the accumulated daily datasets are available at https://doi.org/10.57760/sciencedb.ecodb.00165 (Leng et al., 2023b).

Hydroclimatic processes as the primary drivers of the Early Khvalynian transgression of the Caspian Sea: new developments

Abstract. It has been well established that during the late Quaternary, the Khvalynian transgression of the Caspian Sea occurred, when the sea level rose tens of meters above the present level. Here, we evaluate the physical feasibility of the hypothesis that the maximum phase of this extraordinary event (known as the “Early Khvalynian transgression”) could be initiated and maintained for several thousand years solely by hydroclimatic factors. The hypothesis is based on recent studies dating the highest sea level stage (well above +10 m a.s.l.) to the final period of deglaciation, 17–13 kyr BP, and studies estimating the contribution of the glacial waters in the sea level rise for this period as negligible. To evaluate the hypothesis put forward, we first applied the coupled ocean and sea-ice general circulation model driven by the climate model and estimated the equilibrium water inflow (irrespective of its origin) sufficient to maintain the sea level at the well-dated marks of the Early Khvalynian transgression as 400–470 km3 yr−1. Secondly, we conducted an extensive radiocarbon dating of the large paleochannels (signs of high flow of atmospheric origin) located in the Volga basin and found that the period of their origin (17.5–14 ka BP) is almost identical to the recent dating of the main phase of the Early Khvalynian transgression. Water flow that could form these paleochannels was earlier estimated for the ancient Volga River as 420 km3 yr−1, i.e., close to the equilibrium runoff we determined. Thirdly, we applied a hydrological model forced by paleoclimate data to reveal physically consistent mechanisms of an extraordinarily high water inflow into the Caspian Sea in the absence of a visible glacial meltwater effect. We found that the inflow could be caused by the spread of post-glacial permafrost in the Volga paleocatchment. The numerical experiments demonstrated that the permafrost resulted in a sharp drop in infiltration into the frozen ground and reduced evaporation, which all together generated the Volga runoff during the Oldest Dryas, 17–14.8 kyr BP, up to 360 km3 yr−1 (i.e., the total inflow into the Caspian Sea could reach 450 km3 yr−1). The closeness of the estimates of river inflow into the sea, obtained by three independent methods, in combination with the previously obtained results, gave us reason to conclude that the hypothesis put forward is physically consistent.

Pairing remote sensing and clustering in landscape hydrology for large-scale change identification: an application to the subarctic watershed of the George River (Nunavik, Canada)

Abstract. For remote and vast northern watersheds, hydrological data are often sparse and incomplete. Landscape hydrology provides useful approaches for the indirect assessment of the hydrological characteristics of watersheds through analysis of landscape properties. In this study, we used unsupervised geographic object-based image analysis (GeOBIA) paired with the fuzzy c-means (FCM) clustering algorithm to produce seven high-resolution territorial classifications of key remotely sensed hydro-geomorphic metrics for the 1985–2019 time period, each with a frequency of 5 years. Our study site is the George River watershed (GRW), a 42 000 km2 watershed located in Nunavik, northern Quebec (Canada). The subwatersheds within the GRW, used as the objects of the GeOBIA, were classified as a function of their hydrological similarities. Classification results for the period 2015–2019 showed that the GRW is composed of two main types of subwatersheds distributed along a latitudinal gradient, which indicates broad-scale differences in hydrological regimes and water balances across the GRW. Six classifications were computed for the period 1985–2014 to investigate past changes in hydrological regime. The time series of seven classifications showed a homogenization of subwatershed types associated with increases in vegetation productivity and in water contents in soil and vegetation, mostly concentrated in the northern half of the GRW, which were the major changes occurring in the land cover metrics of the GRW. An increase in vegetation productivity likely contributed to an augmentation in evaporation and may be a primary driver of fundamental shifts in the GRW water balance, potentially explaining a measured decline of about 1 % (∼ 0.16 km3 yr−1) in the George River’s discharge since the mid-1970s. Permafrost degradation over the study period also likely affected the hydrological regime and water balance of the GRW. However, the shifts in permafrost extent and active layer thickness remain difficult to detect using remote-sensing-based approaches, particularly in areas of discontinuous and sporadic permafrost.

Soil erosion, sediment sources, connectivity and suspended sediment yields in UK temperate agricultural catchments: Discrepancies and reconciliation of field-based measurements

Robust understanding of the fine-grained sediment cascades of temperate agricultural catchments is essential for supporting targeted management for addressing the widely reported sediment problem. Within the UK, many independent field-based measurements of soil erosion, sediment sources and catchment suspended sediment yields have been published. However, attempts to review and assess the compatibility of these measurements are limited. The data available suggest that landscape scale net soil erosion rates (∼38 t km−2 yr−1 for arable and ∼26 t km−2 yr−1 grassland) are comparable to the typical suspended sediment yield of a UK catchment (∼44 t km2 yr−1). This finding cannot, however, be reconciled easily with current prevailing knowledge that agricultural topsoils dominate sediment contributions to watercourses, and that catchment sediment delivery ratios are typically low. Channel bank erosion rates can be high at landscape scale (27 km−2 yr−1) and account for these discrepancies but would need to be the dominant sediment source in most catchments, which does not agree with a review of sediment sources for the UK made in the recent past. A simple and robust colour-based sediment source tracing method using hydrogen peroxide sample treatment is therefore used in fifteen catchments to investigate their key sediment sources. Only in two of the catchments are eroding arable fields likely to be important sediment sources, supporting the alternative hypothesis that bank erosion is likely to be the dominant source of sediment in many UK catchments. It is concluded that the existing lines of evidence on the individual components of the fine sediment cascade in temperate agricultural catchments in the UK are difficult to reconcile and run the risk of best management interventions being targeted inappropriately. Recommendations for future research to address paucities in measured erosion rates, sediment delivery ratios and suspended sediment yields, validate sediment source fingerprinting results, consider the sources of sediment-associated organic matter, and re-visit soil erosion and sediment cascade model parameterisation are therefore made.

Assessing the contribution of China's grain production during 2005–2020 from the perspective of the crop-water-land nexus

Water shortages and diversion of arable lands to other uses represent systemic risks to global agricultural production. However, few studies have comprehensively assessed blue-green water and land resources performance in crop cultivation and grain production. This study establishes a crop-water-land nexus accounting framework that distinguishes between blue and green water. Contributions of water and land resources to increases in grain production in China in the years 2005, 2010, 2015 and 2020 were evaluated based on provincial-scale crop-water-land nexus accounting. China produced 580.4 Tg of grain using 805.1 × 103 km2 yr−1 of arable land per year, 76.1 % of which was accounted for by 13 major grain-producing provinces. Annual water consumption in grain production was estimated to be 614.3 × 109 m3, including 183.0 × 109 m3 blue and 431.3 × 109 m3 green water. Albeit with significant spatial variation, land and water resource inputs increased over time. Excluding agronomic improvements, blue water, green water and arable land jointly contributed 65.4 % of the national increase in grain production (185.5 Tg) from 2005 to 2020. Irrigated cropland in major grain-producing provinces dominated grain production increases and national level shifts in water resources over the period studied. The marginal efficiency of blue water (0.784 kg m−3) in grain production was greater than that of green water (0.071 kg m−3). Reclaiming reserve land, upgrading irrigation technology and improving rainwater use efficiency in the provinces along a southwest to northeast axis (e.g., from Heilongjiang to Yunnan), are effective approaches for the country to continue to increase food production in the future.

Implications for sustainable water consumption in Africa by simulating five decades (1965–2014) of groundwater recharge

Groundwater stands as a vital water resource for both present and future generations in Africa. This underscores the importance of examining the sustainability of current groundwater consumption across the continent, along with its capacity to fulfill the current human and essential environmental water needs. Groundwater sustainable yield is a suitable indicator for assessing groundwater sustainability but has not yet been quantified properly across Africa. A thorough quantification of groundwater sustainable yield necessitates a profound comprehension of the spatio-temporal fluctuations in surface hydrology, groundwater recharge, environmental flow, and sectoral water use. In this study, high spatial resolution (10 km) land surface hydrology was simulated for five decades (1965–2014) across Africa by the Community Land Model version 5 at half-hourly time step and aggregated to monthly and annual temporal resolutions. Then, groundwater recharge and environmental flow were quantified based on the water balance approach for the whole continent. Finally, by including African sectoral water use data available for four decades (1971–2010) we obtained the long-term average of groundwater sustainable yield. Based on extensive simulations of long-term land surface hydrology, we discovered that the groundwater system in Africa experienced an average annual recharge of 57.8 mm yr−1 (with a standard deviation of 110.8 mm yr−1 serving as an indicator of spatial variability), corresponding roughly to an annual recharge volume of 1793.6 km3 yr−1. Furthermore, our analysis revealed that the entire continent possesses an annual average potential sustainable yield (with standard deviations) of 4.5 mm yr−1 (10.2), 20.6 mm yr−1 (42.9), and 37.3 mm yr−1 (75.7) under conservative, optimum, and suitable water consumption scenarios, respectively. This calculated annual groundwater sustainable yield corresponds to 141.9 km3 yr−1, 643.1 km3 yr−1, and 1160.5 km3 yr−1 for the conservative, optimum, and suitable scenarios, respectively. Furthermore, the calculated sustainable yield volume is contrasted with the total water storage figures documented for 50 countries throughout Africa. The outcomes illustrate that our calculated annual sustainable yield equates to roughly 0.02%, 0.1%, and 0.17% of the reported groundwater storage across the entire continent. Based on the estimated long-term average sustainable yield and the reported total water storage at the national level, our conclusion is that the accessible groundwater resources could potentially satisfy the current water requirements of both humans and the environment in African countries. This study offers the first model-based estimation of groundwater availability across Africa, potentially serving as a catalyst to inspire further progress toward adopting more sustainable approaches to groundwater usage on the continent.

Streamflow Composition and Water “Imbalance” in the Northern Himalayas

AbstractThe Yarlung Zangbo River (YZR) is the largest river in the northern Himalayas, providing crucial water resources for downstream. A full understanding of the streamflow dynamics and regional water budget is critical to secure water security of the Himalayan water tower. Here we establish a comprehensive hydrological model to simulate the precipitation‐runoff‐evapotranspiration‐groundwater‐streamflow complex in the YZR basin. We decipher contributions of different water sources (e.g., precipitation, meltwater, groundwater) to YZR's streamflow and estimate that groundwater sustains ∼36% of annual streamflow in the YZR, while precipitation and melt surface runoff contribute 40% and 24%, respectively. Combining modeling, observation and reanalysis data, our results reveal a water “imbalance” that ∼31% of annual precipitation and meltwater (∼333 mm yr−1 or ∼85 km3 yr−1) is unaccounted for in the YZR basin. We propose that the “excess water” discharges to deep fractured bedrock aquifers, which is promoted by widespread permeable active structures (e.g., faults, fractures). This hypothesis is supported by groundwater storage (GWS) estimates where inclusion of the deep groundwater bridges the discrepancy between baseflow‐derived (shallow) GWS and those derived from the Gravity Recovery and Climate Experiment satellite data. The deep groundwater most likely flows across basins, bypasses streams, and finally discharges to downstream aquifers in the Indo‐Gangetic Plain as mountain block recharge. This study not only provides a comprehensive analysis of the streamflow composition in the YZR, but also contributes to shaping a more complete picture of the functionality of the Himalayan water tower, highlighting the importance of groundwater in regional water transfers.

China's strictest water policy: Reversing water use trends and alleviating water stress

Growing water problems have promoted the Chinese government to implement the strictest water resources management system (SWRMS), the first national policy that puts into practice the concept of “safe operating space” for human water use. Here, we investigate the impact of the SWRMS on China's water use and water stress based on a newly compiled high-resolution and multi-sectoral water use dataset. Results indicate that China's total water use (TWU) increased significantly from 549 km3 yr-1 to 610 km3 yr-1 between 2000 and 2012 (i.e., the pre-SWRMS period), but decreased remarkably in the post-SWRMS period (2012–2020), reaching 565 km3 yr-1 by the year 2020. The decline in TWU was attributed to the improvements of irrigation and industrial water use efficiency (WUE), which were strictly controlled by the SWRMS at various administrative levels of China. The improved WUE has yielded about ∼90 km3 of water savings per year, freeing 17 prefectures from extreme water stress that affects 6% of China's population and 10% of its GDP. Although the improved WUE caused a significant decrease in TWU, the reduction in China's average water stress was insignificant due to the considerable influence of water availability. We further identified hotspots with great potential for water stress reduction, mainly in northwestern China, and hotspots at high risks of water security, primarily on the North China Plain. This study underscores the crucial role of the SWRMS in addressing China's water shortage and provides valuable insights to other countries grappling with water problems in defining their own “safe water operating spaces”.

Unlocking archival maps of the Hornsund fjord area for monitoring glaciers of the Sørkapp Land peninsula, Svalbard

Abstract. Archival maps are an important source of information on the state of glaciers in polar zones and are very often basic research data for analysing changes in glacier mass, extent, and geometry. However, basing a quantitative analysis on archival maps requires that they be standardised and precisely matched against modern-day cartographic materials. This can be achieved effectively using techniques and tools from the field of geographic information systems (i.e. GIS). The objective of this research was to accurately register archival topographic maps of the area surrounding the Hornsund fjord (southern Spitsbergen) published by the Polish Academy of Sciences and to evaluate their potential for use in studying changes in the geometry of glaciers in the north-western part of the Sørkapp Land peninsula in the following periods: 1961–1990, 1990–2010, and 1961–2010. The area occupied by the investigated glaciers in the north-western Sørkapp Land decreased in the years 1961–2010 by 45.6 km2, i.e. by slightly over 16 %. The rate of glacier area change varied over time and amounted to 0.85 km2 yr−1 in the period 1961–1990 and sped up to 1.05 km2 yr−1 after 1990. This process was accompanied by glacier surface lowering by about 90–100 m for the largest land-terminating glaciers on the peninsula and by up to more than 120 m for tidewater glaciers (above the line marking their 1984 extents). The dataset is now available from the Zenodo web portal: https://doi.org/10.5281/zenodo.4573129 (Dudek and Pętlicki, 2021).

Solar irrigation in sub-Saharan Africa: economic feasibility and development potential

Irrespective of water resource abundance, agriculture in sub-Saharan Africa (SSA) is predominantly rainfed. Along with fertilization, irrigation could support smallholder farmers with stabilizing crop yields, increasing incomes, and achieving food security. A key barrier to irrigation uptake is inadequate rural electricity supply for pumping and distributing water, besides other infrastructure deficits. Here we devise a spatially explicit integrated modelling framework to show that over one third of unmet crop water requirements of 19 major crops in smallholder cropland of SSA could be supplied with standalone solar photovoltaic (PV) irrigation systems that can be paid back by farmers within 20 years. This accounts for 60 km3 yr−1 of blue irrigation water requirements distributed over 55 million ha of currently rainfed harvested area (about 40% of the total). Crucially, we identify 10 million ha with a profit potential >$100 ha−1 yr−1. To finance such distributed small-scale infrastructure deployment and operation, we estimate an average discounted investment requirement of $3 billion yr−1, generating potential profits of over $5 billion yr−1 from increased yields to the smallholder farmers, as well as significant food security and energy access co-benefits. We demonstrate the critical importance of business models and investment incentives, crop prices, and PV & battery costs in shaping the economic feasibility and profitability of solar irrigation. Yet, we find that without strong land and water resources management infrastructure and governance, a widespread deployment of solar pumps may drive an unsustainable exploitation of water sources and reduce environmental flows. Our analysis supports public and private stakeholders seeking to target investments along the water–energy–food–economy–sustainable development nexus.

The precision of satellite-based net irrigation quantification in the Indus and Ganges basins

Abstract. Even though irrigation is the largest direct anthropogenic interference in the natural terrestrial water cycle, limited knowledge of the amount of water applied for irrigation exists. Quantification of irrigation via evapotranspiration (ET) or soil moisture residuals between remote-sensing models and hydrological models, with the latter acting as baselines without the influence of irrigation, have successfully been applied in various regions. Here, we implement a novel ensemble methodology to estimate the precision of ET-based net irrigation quantification by combining different ET and precipitation products in the Indus and Ganges basins. A multi-model calibration of 15 models independently calibrated to simulate rainfed ET was conducted before the irrigation quantification. Based on the ensemble average, the 2003–2013 net irrigation amounts to 233 mm yr−1 (74 km3 yr−1) and 101 mm yr−1 (67 km3 yr−1) in the Indus and Ganges basins, respectively. Net irrigation in the Indus Basin is evenly split between dry and wet periods, whereas 70 % of net irrigation occurs during the dry period in the Ganges Basin. We found that, although annual ET from remote-sensing models varied by 91.5 mm yr−1, net irrigation precision was within 25 mm per season during the dry period for the entire study area, which emphasizes the robustness of the applied multi-model calibration approach. Net irrigation variance was found to decrease as ET uncertainty decreased, which is related to the climatic conditions, i.e., high uncertainty under arid conditions. A variance decomposition analysis showed that ET uncertainty accounted for 73 % of the overall net irrigation variance and that the influence of precipitation uncertainty was seasonally dependent, i.e., with an increase during the monsoon season. The results underline the robustness of the framework to support large-scale sustainable water resource management of irrigated land.

Trade-offs and synergistic relationships in wind erosion in Central Asia over the last 40 years: A Bayesian Network analysis

Wind erosion may have significant effects on both the environment and human activities. Central Asia, a prominently affected region by wind erosion on a global scale, has been the focus of a significant number of studies employing fundamental linear equations to establish causal relationships among the driving factors of wind erosion. However, such approaches neglect the imperative need for comprehensive analysis accounting for the intricate non-linear interactions among multiple factors, thereby potentially leading to distorted assessment outcomes. This study evaluated the multidimensional gradients (temporal, spatial, and vertical) of wind erosion in Central Asia over the last four decades using an enhanced version of the Revised Wind Erosion Equation (RWEQ) model. The Wind Erosion Modulus – Bayesian Network (WIEM-BN) model was developed by incorporating the Wind Erosion Modulus (WIEM) calculated by the RWEQ model as the parent node of the Bayesian Network (BN) and integrating multiple factors that influence the occurrence of wind erosion. The findings revealed a synergistic relationship between precipitation and the Normalized Difference Vegetation Index (NDVI), snowy days, and the Human Influence Index (HII), with trade-off correlations between temperature and precipitation and NDVI and soil moisture. The lowest overall WIEM level in Central Asia was associated with high HII and temperature (10–19 °C) as well as moderate precipitation (180–280 mm) and NDVI (0.18–0.24). Wind erosion in Central Asia varied substantially with Land Use Cover Change (LUCC), with the following drivers receiving precedence: wind speed > windy days > elevation > surface roughness (K') > HII > snowy days. Wind erosion was primarily caused by climate conditions (R = 0.741), with human activities (R = 0.629) acting as a suppressor. This study offered strategies to reduce wind erosion by up to 647.06 t km2 yr−1 in Central Asia, including a greater emphasis on ecological conservation programs and increased plant cover.

Contribution of Fresh Submarine Groundwater Discharge to the Gulf of Alaska

AbstractHigh latitude mountain environments are experiencing disproportionately adverse effects from climate change. The Gulf of Alaska (GoA) region is an embodiment of this change, particularly concerning a shifting hydrologic balance. Even so, the magnitude and contribution of fresh submarine groundwater discharge (fresh SGD) remains virtually unexplored within the region, though it has gained increasing attention globally due to its chemical significance and influence on coastal ecosystems. Here we provide the first regional estimates of fresh SGD to the GoA using two established water balance approaches. This is an effective way to distinguish the contribution of terrestrially derived fresh SGD, rather than the more commonly quantified total SGD which includes discharge that is driven by marine forces such as sea‐level oscillations and density gradients. We compare the approaches and assess their capabilities in computing the magnitude of fresh SGD over a large regional scale. Mean annual fresh SGD flux ranges between 26.5 and 86.8 km3 yr−1 to the GoA, equivalent to 3.5%–11.4% of the total freshwater discharge. Contributions are highest in the Southeastern panhandle and lowest in the Cook Inlet basin, with the highest area normalized contribution occurring in the Prince William Sound. Fresh SGD exhibits high spatial and temporal variability throughout the region. Although freshwater discharge to the GoA is investigated considerably, the importance of fresh SGD has, thus far, been overlooked.